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Publisher: Elsevier   (Total: 3184 journals)

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Showing 1 - 200 of 3184 Journals sorted alphabetically
Academic Pediatrics     Hybrid Journal   (Followers: 37, SJR: 1.655, CiteScore: 2)
Academic Radiology     Hybrid Journal   (Followers: 26, SJR: 1.015, CiteScore: 2)
Accident Analysis & Prevention     Partially Free   (Followers: 100, SJR: 1.462, CiteScore: 3)
Accounting Forum     Hybrid Journal   (Followers: 28, SJR: 0.932, CiteScore: 2)
Accounting, Organizations and Society     Hybrid Journal   (Followers: 40, SJR: 1.771, CiteScore: 3)
Achievements in the Life Sciences     Open Access   (Followers: 6)
Acta Anaesthesiologica Taiwanica     Open Access   (Followers: 7)
Acta Astronautica     Hybrid Journal   (Followers: 436, SJR: 0.758, CiteScore: 2)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 2)
Acta Biomaterialia     Hybrid Journal   (Followers: 28, SJR: 1.967, CiteScore: 7)
Acta Colombiana de Cuidado Intensivo     Full-text available via subscription   (Followers: 3)
Acta de Investigación Psicológica     Open Access   (Followers: 3)
Acta Ecologica Sinica     Open Access   (Followers: 11, SJR: 0.18, CiteScore: 1)
Acta Histochemica     Hybrid Journal   (Followers: 3, SJR: 0.661, CiteScore: 2)
Acta Materialia     Hybrid Journal   (Followers: 307, SJR: 3.263, CiteScore: 6)
Acta Mathematica Scientia     Full-text available via subscription   (Followers: 5, SJR: 0.504, CiteScore: 1)
Acta Mechanica Solida Sinica     Full-text available via subscription   (Followers: 9, SJR: 0.542, CiteScore: 1)
Acta Oecologica     Hybrid Journal   (Followers: 12, SJR: 0.834, CiteScore: 2)
Acta Otorrinolaringologica (English Edition)     Full-text available via subscription  
Acta Otorrinolaringológica Española     Full-text available via subscription   (Followers: 2, SJR: 0.307, CiteScore: 0)
Acta Pharmaceutica Sinica B     Open Access   (Followers: 1, SJR: 1.793, CiteScore: 6)
Acta Poética     Open Access   (Followers: 4, SJR: 0.101, CiteScore: 0)
Acta Psychologica     Hybrid Journal   (Followers: 25, SJR: 1.331, CiteScore: 2)
Acta Sociológica     Open Access   (Followers: 1)
Acta Tropica     Hybrid Journal   (Followers: 6, SJR: 1.052, CiteScore: 2)
Acta Urológica Portuguesa     Open Access  
Actas Dermo-Sifiliograficas     Full-text available via subscription   (Followers: 3, SJR: 0.374, CiteScore: 1)
Actas Dermo-Sifiliográficas (English Edition)     Full-text available via subscription   (Followers: 2)
Actas Urológicas Españolas     Full-text available via subscription   (Followers: 3, SJR: 0.344, CiteScore: 1)
Actas Urológicas Españolas (English Edition)     Full-text available via subscription   (Followers: 1)
Actualites Pharmaceutiques     Full-text available via subscription   (Followers: 7, SJR: 0.19, CiteScore: 0)
Actualites Pharmaceutiques Hospitalieres     Full-text available via subscription   (Followers: 3)
Acupuncture and Related Therapies     Hybrid Journal   (Followers: 8)
Acute Pain     Full-text available via subscription   (Followers: 15, SJR: 2.671, CiteScore: 5)
Ad Hoc Networks     Hybrid Journal   (Followers: 11, SJR: 0.53, CiteScore: 4)
Addictive Behaviors     Hybrid Journal   (Followers: 18, SJR: 1.29, CiteScore: 3)
Addictive Behaviors Reports     Open Access   (Followers: 9, SJR: 0.755, CiteScore: 2)
Additive Manufacturing     Hybrid Journal   (Followers: 11, SJR: 2.611, CiteScore: 8)
Additives for Polymers     Full-text available via subscription   (Followers: 23)
Advanced Drug Delivery Reviews     Hybrid Journal   (Followers: 183, SJR: 4.09, CiteScore: 13)
Advanced Engineering Informatics     Hybrid Journal   (Followers: 12, SJR: 1.167, CiteScore: 4)
Advanced Powder Technology     Hybrid Journal   (Followers: 17, SJR: 0.694, CiteScore: 3)
Advances in Accounting     Hybrid Journal   (Followers: 9, SJR: 0.277, CiteScore: 1)
Advances in Agronomy     Full-text available via subscription   (Followers: 17, SJR: 2.384, CiteScore: 5)
Advances in Anesthesia     Full-text available via subscription   (Followers: 29, SJR: 0.126, CiteScore: 0)
Advances in Antiviral Drug Design     Full-text available via subscription   (Followers: 2)
Advances in Applied Mathematics     Full-text available via subscription   (Followers: 11, SJR: 0.992, CiteScore: 1)
Advances in Applied Mechanics     Full-text available via subscription   (Followers: 11, SJR: 1.551, CiteScore: 4)
Advances in Applied Microbiology     Full-text available via subscription   (Followers: 24, SJR: 2.089, CiteScore: 5)
Advances In Atomic, Molecular, and Optical Physics     Full-text available via subscription   (Followers: 15, SJR: 0.572, CiteScore: 2)
Advances in Biological Regulation     Hybrid Journal   (Followers: 4, SJR: 2.61, CiteScore: 7)
Advances in Botanical Research     Full-text available via subscription   (Followers: 2, SJR: 0.686, CiteScore: 2)
Advances in Cancer Research     Full-text available via subscription   (Followers: 33, SJR: 3.043, CiteScore: 6)
Advances in Carbohydrate Chemistry and Biochemistry     Full-text available via subscription   (Followers: 9, SJR: 1.453, CiteScore: 2)
Advances in Catalysis     Full-text available via subscription   (Followers: 5, SJR: 1.992, CiteScore: 5)
Advances in Cell Aging and Gerontology     Full-text available via subscription   (Followers: 5)
Advances in Cellular and Molecular Biology of Membranes and Organelles     Full-text available via subscription   (Followers: 14)
Advances in Chemical Engineering     Full-text available via subscription   (Followers: 29, SJR: 0.156, CiteScore: 1)
Advances in Child Development and Behavior     Full-text available via subscription   (Followers: 10, SJR: 0.713, CiteScore: 1)
Advances in Chronic Kidney Disease     Full-text available via subscription   (Followers: 10, SJR: 1.316, CiteScore: 2)
Advances in Clinical Chemistry     Full-text available via subscription   (Followers: 26, SJR: 1.562, CiteScore: 3)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 20, SJR: 1.977, CiteScore: 8)
Advances in Computers     Full-text available via subscription   (Followers: 14, SJR: 0.205, CiteScore: 1)
Advances in Dermatology     Full-text available via subscription   (Followers: 15)
Advances in Developmental Biology     Full-text available via subscription   (Followers: 13)
Advances in Digestive Medicine     Open Access   (Followers: 12)
Advances in DNA Sequence-Specific Agents     Full-text available via subscription   (Followers: 7)
Advances in Drug Research     Full-text available via subscription   (Followers: 26)
Advances in Ecological Research     Full-text available via subscription   (Followers: 43, SJR: 2.524, CiteScore: 4)
Advances in Engineering Software     Hybrid Journal   (Followers: 29, SJR: 1.159, CiteScore: 4)
Advances in Experimental Biology     Full-text available via subscription   (Followers: 8)
Advances in Experimental Social Psychology     Full-text available via subscription   (Followers: 51, SJR: 5.39, CiteScore: 8)
Advances in Exploration Geophysics     Full-text available via subscription   (Followers: 1)
Advances in Fluorine Science     Full-text available via subscription   (Followers: 9)
Advances in Food and Nutrition Research     Full-text available via subscription   (Followers: 65, SJR: 0.591, CiteScore: 2)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 17)
Advances in Genetics     Full-text available via subscription   (Followers: 21, SJR: 1.354, CiteScore: 4)
Advances in Genome Biology     Full-text available via subscription   (Followers: 10, SJR: 12.74, CiteScore: 13)
Advances in Geophysics     Full-text available via subscription   (Followers: 7, SJR: 1.193, CiteScore: 3)
Advances in Heat Transfer     Full-text available via subscription   (Followers: 26, SJR: 0.368, CiteScore: 1)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 11, SJR: 0.749, CiteScore: 3)
Advances in Human Factors/Ergonomics     Full-text available via subscription   (Followers: 24)
Advances in Imaging and Electron Physics     Full-text available via subscription   (Followers: 3, SJR: 0.193, CiteScore: 0)
Advances in Immunology     Full-text available via subscription   (Followers: 36, SJR: 4.433, CiteScore: 6)
Advances in Inorganic Chemistry     Full-text available via subscription   (Followers: 10, SJR: 1.163, CiteScore: 2)
Advances in Insect Physiology     Full-text available via subscription   (Followers: 2, SJR: 1.938, CiteScore: 3)
Advances in Integrative Medicine     Hybrid Journal   (Followers: 6, SJR: 0.176, CiteScore: 0)
Advances in Intl. Accounting     Full-text available via subscription   (Followers: 3)
Advances in Life Course Research     Hybrid Journal   (Followers: 9, SJR: 0.682, CiteScore: 2)
Advances in Lipobiology     Full-text available via subscription   (Followers: 1)
Advances in Magnetic and Optical Resonance     Full-text available via subscription   (Followers: 8)
Advances in Marine Biology     Full-text available via subscription   (Followers: 21, SJR: 0.88, CiteScore: 2)
Advances in Mathematics     Full-text available via subscription   (Followers: 12, SJR: 3.027, CiteScore: 2)
Advances in Medical Sciences     Hybrid Journal   (Followers: 8, SJR: 0.694, CiteScore: 2)
Advances in Medicinal Chemistry     Full-text available via subscription   (Followers: 6)
Advances in Microbial Physiology     Full-text available via subscription   (Followers: 5, SJR: 1.158, CiteScore: 3)
Advances in Molecular and Cell Biology     Full-text available via subscription   (Followers: 24)
Advances in Molecular and Cellular Endocrinology     Full-text available via subscription   (Followers: 8)
Advances in Molecular Toxicology     Full-text available via subscription   (Followers: 7, SJR: 0.182, CiteScore: 0)
Advances in Nanoporous Materials     Full-text available via subscription   (Followers: 5)
Advances in Oncobiology     Full-text available via subscription   (Followers: 2)
Advances in Organ Biology     Full-text available via subscription   (Followers: 2)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 18, SJR: 1.875, CiteScore: 4)
Advances in Parallel Computing     Full-text available via subscription   (Followers: 7, SJR: 0.174, CiteScore: 0)
Advances in Parasitology     Full-text available via subscription   (Followers: 5, SJR: 1.579, CiteScore: 4)
Advances in Pediatrics     Full-text available via subscription   (Followers: 27, SJR: 0.461, CiteScore: 1)
Advances in Pharmaceutical Sciences     Full-text available via subscription   (Followers: 18)
Advances in Pharmacology     Full-text available via subscription   (Followers: 17, SJR: 1.536, CiteScore: 3)
Advances in Physical Organic Chemistry     Full-text available via subscription   (Followers: 9, SJR: 0.574, CiteScore: 1)
Advances in Phytomedicine     Full-text available via subscription  
Advances in Planar Lipid Bilayers and Liposomes     Full-text available via subscription   (Followers: 3, SJR: 0.109, CiteScore: 1)
Advances in Plant Biochemistry and Molecular Biology     Full-text available via subscription   (Followers: 10)
Advances in Plant Pathology     Full-text available via subscription   (Followers: 6)
Advances in Porous Media     Full-text available via subscription   (Followers: 5)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 19)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 20, SJR: 0.791, CiteScore: 2)
Advances in Psychology     Full-text available via subscription   (Followers: 66)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 6, SJR: 0.371, CiteScore: 1)
Advances in Radiation Oncology     Open Access   (Followers: 1, SJR: 0.263, CiteScore: 1)
Advances in Small Animal Medicine and Surgery     Hybrid Journal   (Followers: 3, SJR: 0.101, CiteScore: 0)
Advances in Space Biology and Medicine     Full-text available via subscription   (Followers: 6)
Advances in Space Research     Full-text available via subscription   (Followers: 421, SJR: 0.569, CiteScore: 2)
Advances in Structural Biology     Full-text available via subscription   (Followers: 5)
Advances in Surgery     Full-text available via subscription   (Followers: 13, SJR: 0.555, CiteScore: 2)
Advances in the Study of Behavior     Full-text available via subscription   (Followers: 37, SJR: 2.208, CiteScore: 4)
Advances in Veterinary Medicine     Full-text available via subscription   (Followers: 20)
Advances in Veterinary Science and Comparative Medicine     Full-text available via subscription   (Followers: 15)
Advances in Virus Research     Full-text available via subscription   (Followers: 5, SJR: 2.262, CiteScore: 5)
Advances in Water Resources     Hybrid Journal   (Followers: 53, SJR: 1.551, CiteScore: 3)
Aeolian Research     Hybrid Journal   (Followers: 6, SJR: 1.117, CiteScore: 3)
Aerospace Science and Technology     Hybrid Journal   (Followers: 383, SJR: 0.796, CiteScore: 3)
AEU - Intl. J. of Electronics and Communications     Hybrid Journal   (Followers: 8, SJR: 0.42, CiteScore: 2)
African J. of Emergency Medicine     Open Access   (Followers: 6, SJR: 0.296, CiteScore: 0)
Ageing Research Reviews     Hybrid Journal   (Followers: 12, SJR: 3.671, CiteScore: 9)
Aggression and Violent Behavior     Hybrid Journal   (Followers: 475, SJR: 1.238, CiteScore: 3)
Agri Gene     Hybrid Journal   (Followers: 1, SJR: 0.13, CiteScore: 0)
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 18, SJR: 1.818, CiteScore: 5)
Agricultural Systems     Hybrid Journal   (Followers: 31, SJR: 1.156, CiteScore: 4)
Agricultural Water Management     Hybrid Journal   (Followers: 45, SJR: 1.272, CiteScore: 3)
Agriculture and Agricultural Science Procedia     Open Access   (Followers: 4)
Agriculture and Natural Resources     Open Access   (Followers: 3)
Agriculture, Ecosystems & Environment     Hybrid Journal   (Followers: 58, SJR: 1.747, CiteScore: 4)
Ain Shams Engineering J.     Open Access   (Followers: 5, SJR: 0.589, CiteScore: 3)
Air Medical J.     Hybrid Journal   (Followers: 7, SJR: 0.26, CiteScore: 0)
AKCE Intl. J. of Graphs and Combinatorics     Open Access   (SJR: 0.19, CiteScore: 0)
Alcohol     Hybrid Journal   (Followers: 12, SJR: 1.153, CiteScore: 3)
Alcoholism and Drug Addiction     Open Access   (Followers: 11)
Alergologia Polska : Polish J. of Allergology     Full-text available via subscription   (Followers: 1)
Alexandria Engineering J.     Open Access   (Followers: 2, SJR: 0.604, CiteScore: 3)
Alexandria J. of Medicine     Open Access   (Followers: 1, SJR: 0.191, CiteScore: 1)
Algal Research     Partially Free   (Followers: 11, SJR: 1.142, CiteScore: 4)
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 2)
Allergologia et Immunopathologia     Full-text available via subscription   (Followers: 1, SJR: 0.504, CiteScore: 1)
Allergology Intl.     Open Access   (Followers: 5, SJR: 1.148, CiteScore: 2)
Alpha Omegan     Full-text available via subscription   (SJR: 3.521, CiteScore: 6)
ALTER - European J. of Disability Research / Revue Européenne de Recherche sur le Handicap     Full-text available via subscription   (Followers: 10, SJR: 0.201, CiteScore: 1)
Alzheimer's & Dementia     Hybrid Journal   (Followers: 54, SJR: 4.66, CiteScore: 10)
Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring     Open Access   (Followers: 6, SJR: 1.796, CiteScore: 4)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (Followers: 6, SJR: 1.108, CiteScore: 3)
Ambulatory Pediatrics     Hybrid Journal   (Followers: 5)
American Heart J.     Hybrid Journal   (Followers: 58, SJR: 3.267, CiteScore: 4)
American J. of Cardiology     Hybrid Journal   (Followers: 63, SJR: 1.93, CiteScore: 3)
American J. of Emergency Medicine     Hybrid Journal   (Followers: 46, SJR: 0.604, CiteScore: 1)
American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 12)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 14, SJR: 1.524, CiteScore: 3)
American J. of Human Genetics     Hybrid Journal   (Followers: 37, SJR: 7.45, CiteScore: 8)
American J. of Infection Control     Hybrid Journal   (Followers: 29, SJR: 1.062, CiteScore: 2)
American J. of Kidney Diseases     Hybrid Journal   (Followers: 36, SJR: 2.973, CiteScore: 4)
American J. of Medicine     Hybrid Journal   (Followers: 50)
American J. of Medicine Supplements     Full-text available via subscription   (Followers: 3, SJR: 1.967, CiteScore: 2)
American J. of Obstetrics and Gynecology     Hybrid Journal   (Followers: 248, SJR: 2.7, CiteScore: 4)
American J. of Ophthalmology     Hybrid Journal   (Followers: 66, SJR: 3.184, CiteScore: 4)
American J. of Ophthalmology Case Reports     Open Access   (Followers: 5, SJR: 0.265, CiteScore: 0)
American J. of Orthodontics and Dentofacial Orthopedics     Full-text available via subscription   (Followers: 6, SJR: 1.289, CiteScore: 1)
American J. of Otolaryngology     Hybrid Journal   (Followers: 25, SJR: 0.59, CiteScore: 1)
American J. of Pathology     Hybrid Journal   (Followers: 32, SJR: 2.139, CiteScore: 4)
American J. of Preventive Medicine     Hybrid Journal   (Followers: 28, SJR: 2.164, CiteScore: 4)
American J. of Surgery     Hybrid Journal   (Followers: 39, SJR: 1.141, CiteScore: 2)
American J. of the Medical Sciences     Hybrid Journal   (Followers: 12, SJR: 0.767, CiteScore: 1)
Ampersand : An Intl. J. of General and Applied Linguistics     Open Access   (Followers: 7)
Anaerobe     Hybrid Journal   (Followers: 4, SJR: 1.144, CiteScore: 3)
Anaesthesia & Intensive Care Medicine     Full-text available via subscription   (Followers: 66, SJR: 0.138, CiteScore: 0)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 24, SJR: 0.411, CiteScore: 1)
Anales de Cirugia Vascular     Full-text available via subscription   (Followers: 1)
Anales de Pediatría     Full-text available via subscription   (Followers: 3, SJR: 0.277, CiteScore: 0)
Anales de Pediatría (English Edition)     Full-text available via subscription  
Anales de Pediatría Continuada     Full-text available via subscription  
Analytic Methods in Accident Research     Hybrid Journal   (Followers: 5, SJR: 4.849, CiteScore: 10)
Analytica Chimica Acta     Hybrid Journal   (Followers: 44, SJR: 1.512, CiteScore: 5)
Analytica Chimica Acta : X     Open Access  
Analytical Biochemistry     Hybrid Journal   (Followers: 209, SJR: 0.633, CiteScore: 2)
Analytical Chemistry Research     Open Access   (Followers: 13, SJR: 0.411, CiteScore: 2)
Analytical Spectroscopy Library     Full-text available via subscription   (Followers: 14)
Anesthésie & Réanimation     Full-text available via subscription   (Followers: 2)
Anesthesiology Clinics     Full-text available via subscription   (Followers: 25, SJR: 0.683, CiteScore: 2)
Angiología     Full-text available via subscription   (SJR: 0.121, CiteScore: 0)
Angiologia e Cirurgia Vascular     Open Access   (Followers: 1, SJR: 0.111, CiteScore: 0)
Animal Behaviour     Hybrid Journal   (Followers: 218, SJR: 1.58, CiteScore: 3)
Animal Feed Science and Technology     Hybrid Journal   (Followers: 6, SJR: 0.937, CiteScore: 2)
Animal Reproduction Science     Hybrid Journal   (Followers: 7, SJR: 0.704, CiteScore: 2)

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Similar Journals
Journal Cover
Additive Manufacturing
Journal Prestige (SJR): 2.611
Citation Impact (citeScore): 8
Number of Followers: 11  
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 2214-8604
Published by Elsevier Homepage  [3184 journals]
  • Microstructural evolution and mechanical behavior of nickel aluminum
           bronze Cu-9Al-4Fe-4Ni-1Mn fabricated through wire-arc additive
    • Abstract: Publication date: Available online 13 September 2019Source: Additive ManufacturingAuthor(s): C. Dharmendra, A. Hadadzadeh, B.S. Amirkhiz, G.D. Janaki Ram, M. Mohammadi As a step forward toward the development of the next generation of nickel aluminum bronze (NAB) components using wire-arc additive manufacturing (WAAM), square bars were printed in the vertical direction. The as-built microstructure was characterized using multi-scale electron microscopy techniques, where the differences in phase formation were compared to the reference cast-NAB based on the solidification characteristics. The as-cast microstructure typically consists of Cu-rich α-matrix, and four types of intermetallic particles referred to as κ-phases. In the WAAM-NAB, the formation of κI was suppressed due to high cooling rates. The microstructure was finer and the volume fraction of intermetallic particles was significantly lower than that of the cast-NAB. Based on energy dispersive spectroscopy (EDS) technique and diffraction pattern analysis using transmission electron microscopy (TEM), the phases formed in the interdendritic regions were identified as κII (globular Fe3Al) and κIII (lamellar NiAl), whereas numerous fine (5-10 nm) Fe-rich κIV particles were precipitated uniformly within the α-matrix. Electron backscatter diffraction analysis revealed weak texture on both parallel and perpendicular planes to the building direction with (100) poles rotated away from the build direction. The WAAM-NAB sample exhibited considerably higher yield strength (˜88 MPa) and elongation (˜10%) than the cast-NAB, but the gain in the ultimate tensile strength was marginal.Graphical abstractGraphical abstract for this article
  • Laboratory X-ray tomography for metal additive manufacturing: round robin
    • Abstract: Publication date: Available online 13 September 2019Source: Additive ManufacturingAuthor(s): Anton du Plessis, Stephan G. le Roux, Jess Waller, Philip Sperling, Nils Achilles, Andre Beerlink, Jean-François Métayer, Mirko Sinico, Gabriel Probst, Wim Dewulf, Florian Bittner, Hans-Josef Endres, Marian Willner, Ágota Drégelyi-Kiss, Tomas Zikmund, Jakub Laznovsky, Jozef Kaiser, Pascal Pinter, Stefan Dietrich, Elena Lopez This paper reports on the results of a round robin test conducted by ten X-ray micro computed tomography (micro-CT) laboratories with the same three selected titanium alloy (Ti6Al4V) laser powder bed fusion (L-PBF) test parts. These parts were a 10-mm cube, a 60-mm long and 40-mm high complex-shaped bracket, and a 15-mm diameter rod. Previously developed protocols for micro-CT analysis of these parts were provided to all participants, including suggested scanning parameters and image analysis steps. No further information on the samples were provided, and they were selected from a variety of parts from a previous different type of round robin study where various L-PBF laboratories provided identical parts for micro-CT analysis at one laboratory. In this new micro-CT round robin test which involves various micro-CT laboratories, parts from the previous work were selected such that each part had a different characteristic flaw type, and all laboratories involved in the study analyzed the same set of parts. The 10-mm cube contained subsurface pores just under its top surface (relative to build direction), and all participants could positively identify this. The complex bracket had contour pores around its outer vertical sides, and was warped with two arms deflected towards one another. Both of these features were positively identified by all participants. The 15-mm diameter rod had a layered stop/start flaw, which was also positively identified by all participants. Differences were found among participants for quantitative evaluations, ranging from no quantitative measurement made, to under and overestimation of the values in all analyses attempted. This round robin provides the opportunity to highlight typical causes of errors in micro-CT scanning and image analysis as applied to additively manufactured parts. Some workflow variations, sources of error and ways to increase the reproducibility of such analysis workflows are discussed. The ultimate aim of this work is to advance the efficient use of micro-CT facilities for process optimization and quality inspections for additively manufactured products. The results provide confidence in the use of laboratory micro-CT but also indicate the need for further development of standards, protocols and image analysis workflows for quantitative assessment, especially for direct and quantitative comparisons between different laboratories.
  • 3D Printed High Functional Density Packaging Compatible Out-of-Plane
    • Abstract: Publication date: Available online 12 September 2019Source: Additive ManufacturingAuthor(s): Mohd Ifwat Mohd Ghazali, Saranraj Karuppuswami, Amanpreet Kaur, Premjeet Chahal This paper demonstrates a simple, low-cost additive manufacturing technique for fabricating structures compatible with high-density packaging solutions. Leveraging the third dimension (z-axis), several out-of-plane (non-planar) antennas that are compatible with multi-layer integration are presented, including an elevated vertical mount patch antenna, an air-gap based E-Patch antenna, a monopole with a corner reflector, and a vertical Yagi-Uda antenna. A T-line resonator is characterized to understand the transmission line losses associated with the vertical bends. Details of the simulation, fabrication, and measurements are presented. Simulations are carried out using ANSYS High-Frequency Structure Simulator (HFSS®), and structures are fabricated using a polyjet printing process. The measured results are in good agreement with the simulation results, and overall a good performance is achieved for all the antenna designs. For example, the elevated vertical mount patch shows a gain of 3.62 dBi (center frequency of 5.4 GHz), and the air-gap E-patch antenna shows a gain of 6 dBi at 2.4 GHz and 10 dB bandwidth of 4.9 GHz. The vertical monopole antenna with a corner reflector shows a peak gain of 7.3 dBi at 6 GHz, and the Yagi-Uda antenna shows a forward gain of 6 dBi at 5 GHz.
  • Parametric Analysis to Quantify Process Input Influence on the Printed
           Densities of Binder Jetted Alumina Ceramics
    • Abstract: Publication date: Available online 9 September 2019Source: Additive ManufacturingAuthor(s): Edgar Mendoza Jimenez, Daming Ding, Laisuo Su, Aparna R. Joshi, Aarti Singh, B. Reeja-Jayan, Jack Beuth Binder jetting, a commercial additive manufacturing process that selectively deposits a liquid binder onto a powder bed, can become a viable method to additively manufacture ceramics. However, the effects of process parameters/inputs on printing outputs (e.g. part density and geometric resolution) have not been investigated and no methodical approach exists for the process development of new materials. In this work, a parametric study consisting of 18 experiments with unique process input combinations explores the influence of seven process inputs on the relative densities of as-printed (green) alumina (Al2O3) parts. Sensitivity analyses compare the influence of each input on green densities. Multivariable linear and Gaussian process regressions provide models for predicting green densities as a function of binder jetting process inputs. The parametric study reveals that two process inputs, namely recoat speed and oscillator speed, significantly influence green densities. The multivariable linear and Gaussian process regression models indicate that the green densities of alumina builds can be increased by decreasing the recoat speed and increasing the oscillator speed. The Gaussian process regression model further suggests that the green densities have nonlinear dependence on the rest of the process parameters. Separate prints were performed at process input combinations different than those of the parametric study to validate the green density models. The models produced can assist operators in selecting process inputs that will result in a desired green density, allowing for the control of porosity in printed parts with a high degree of accuracy. The methodology reported in this study can be leveraged for other powder systems and machines to predict and control the porosity of binder jetted parts for applications such as filters, bearings, electronics, and medical implants.
  • Fused filament fabrication, debinding and sintering as a low cost additive
           manufacturing method of 316L Stainless Steel
    • Abstract: Publication date: Available online 9 September 2019Source: Additive ManufacturingAuthor(s): Yvonne Thompson, Joamin Gonzalez-Gutierrez, Christian Kukla, Peter Felfer By using filaments comprising metal or ceramic powders and polymer binders, solid metal and ceramic parts can be created by combining low-cost fused filament fabrication (FFF) with debinding and sintering. In this work, we explored a fabrication route using a FFF filament filled with 316 L steel powder at 55 vol.-%. We investigated the printing, debinding and sintering parameters and optimized them with respect to the mechanical properties of the final part. Special focus was placed on debinding and sintering in order to obtain components of low residual porosity. Solvent debinding of the printed green bodies created an internal network of interconnected pores and was followed by thermal debinding. Thermal debinding allowed for complete removal of the remaining binder and produced mechanically stable brown parts. Sintering at 1360 °C provided densification of the parts and generated nearly isotropic linear shrinkage of about 20 %. Using optimized parameters, it was possible to fabricate 316 L steel components with a density greater than 95 % via the material extrusion additive manufacturing, debinding and sintering route, with achievable deflections in a 3-point bending test similar to rolled sheet material, albeit at lower strength.
  • Analytical modeling and experimental validation of powder stream
           distribution during direct energy deposition
    • Abstract: Publication date: Available online 7 September 2019Source: Additive ManufacturingAuthor(s): Zhichao Liu, Hong-Chao Zhang, Shitong Peng, Hoyeol Kim, Dongping Du, Weilong Cong As an important factor during direct energy deposition (DED) additive manufacturing process, powder stream distribution will not only affect the deposition rate, but also the powder-gas and power-powder interactions, and thus the consequent quality and property of the fabricated part. This paper created an analytical model to illustrate the powder stream distribution under the four-jet nozzles in the DED. To validate the proposed model, weight measurement method was used to track the powder stream distributions at different positions under the nozzle. Additionally, the effects of the input variables, including powder flow rate, gas flow rate and particle size, on the powder stream distribution were also analyzed. The results suggest a relatively good agreement between the modelling and experimental measurements. At the end, the powder deposition efficiency (PDE) was estimated based on the simulation results.
  • Production of net-shape Mn-Al permanent magnets by electron beam melting
    • Abstract: Publication date: Available online 6 September 2019Source: Additive ManufacturingAuthor(s): I.A. Radulov, V.V. Popov, A. Koptyug, F. Maccari, A. Kovalevsky, S. Essel, J. Gassmann, K.P. Skokov, M. Bamberger The main goal of this work is the adoption of additive manufacturing for the production of inexpensive rare-earth free MnAl-based permanent magnets. The use of more advanced binder-free additive manufacturing technique such as Electron Beam Melting (EBM) allows obtaining fully-dense magnetic materials with advanced topology and complex shapes. We focus on the feasibility of controlling the phase formation in additively manufactured Mn-Al alloys by employing post-manufacturing heat treatment. The as-manufactured EBM samples contain 8% of the desired ferromagnetic τ-MnAl phase. After the optimized annealing treatment, the content of the τ-phase was increased to 90%. This sample has a coercivity value of 0.15 T, which is also the maximum achieved in conventionally produced binary MnAl magnets. Moreover, the EBM samples are fully dense and have the same density as the samples produced by conventional melting density.
  • Strong and light cellular silicon carbonitride – reduced graphene oxide
           material with enhanced electrical conductivity and capacitive response
    • Abstract: Publication date: Available online 6 September 2019Source: Additive ManufacturingAuthor(s): J.J. Moyano, J. Mosa, M. Aparicio, D. Pérez-Coll, M. Belmonte, P. Miranzo, M.I. Osendi Steady graphene oxide (GO) scaffolds created by direct ink writing are used to develop a silicon carbonitride (SiCN) -graphene oxide hybrid material through a preceramic polymer route. For achieving mechanically stable GO scaffolds, the drying method is critical as the ink contains 5 wt.% of GO, 10 wt.% of polyelectrolytes and 85 wt.% of water. The liquid preceramic polymer (polysilazane type) quickly infiltrates the 3D scaffolds, under vacuum conditions, entirely covering the GO network creating a replica of the original scaffold. The hybrid cellular structure -once thermally treated for GO reduction and ceramic conversion- consists of a network of reduced GO (∼10 wt.%) embedded in an amorphous SiCN matrix following the designed architecture. The 3D hybrid structures show notable electrical conductivity (890 S m-1 at room temperature), thermal stability and considerable strength, about 20 times higher than the single GO scaffold. The structures are tested as electrodes for supercapacitors, reaching a gravimetric capacitance of 39 F g-1 that remains stable after 7000 charge/discharge cycles.Graphical abstractGraphical abstract for this article
  • Thermal Conductivity of TPMS Lattice Structures Manufactured via Laser
           Powder Bed Fusion
    • Abstract: Publication date: Available online 5 September 2019Source: Additive ManufacturingAuthor(s): S. Catchpole-Smith, R.R.J. Sélo, A.W. Davis, I.A. Ashcroft, C.J. Tuck, A. Clare Lattice structures can add value to high-performance components manufactured by laser powder bed fusion due to their high specific strength and stiffness. A further use of lattice structures is in thermo-mechanical applications, where the high surface area of the lattice may aid heat transfer. However, little characterisation of lattices under thermal loading is currently available in the literature. In this study, a custom-built test rig was used to characterise the thermal conduction for three triply periodic minimal surface lattice types, namely: gyroid, diamond and Schwarz primitives, with unit cell size and volume fraction being varied.Results show that thermal conductivity is primarily a function of the material properties and volume fraction of the sample. However, some effects of the geometry, such as surface area to volume ratio, can be used to explain slight differences in the measured conductivity. The Schwarz primitive unit cell consistently gave the highest conductivity, with diamond and gyroid unit cells being marginally lower. Larger cell sizes typically gave higher conductivity than smaller cells, which can be attributed to greater intra-cell convective heat transfer and better interface coupling with the testing apparatus.The experimental results are used to derive equations that allow samples with a specified thermal conductivity to be designed, thus demonstrating how a component may be manufactured with a custom thermal profile by varying the volume fraction of the lattice.
  • Part Geometry and Conduction-based Laser Power Control for Powder Bed
           Fusion Additive Manufacturing
    • Abstract: Publication date: Available online 4 September 2019Source: Additive ManufacturingAuthor(s): Ho Yeung, Brandon Lane, Jason Fox Laser powder bed fusion (LPBF) uses a focused, high power laser to repeatedly scan geometric patterns on thin layers of metal powder, which build up to a final, solid three-dimensional (3D) part. This process is somewhat limited in that the parts tend to have poorer surface finish (compared to machining or grinding) and distortion due to residual stress, as well as multiple other deficiencies. Typical laser scan strategies are relatively simple and use constant laser power levels. This elicits local variations in the melt pool size, shape, or temperature, particularly near sharp geometric features or overhang structures due to the relatively higher thermal conductivity of solid metal compared to metal powder. In this paper, we present a new laser power control algorithm, which scales the laser power to a value called the geometric conductance factor (GCF). The GCF is calculated based on the amount of solid vs. powder material near the melt pool. The algorithm for calculating GCF is presented along with some basic examples for clarification. Then, we detail the hardware and software implementation on the National Institute of Standards and Technology (NIST) additive manufacturing metrology testbed (AMMT), which includes co-axial melt pool monitoring using a high-speed camera. Six parts were fabricated out of nickel superalloy 625 (IN625) with the same nominal laser power, but with varying GCF algorithm parameters. We demonstrate the effect of tailored laser power on reducing the variability of melt pool intensity measured throughout the 3D build. Finally, we contrast the difference between the ‘optimized’ part vs. the standard build parameters, including the deflection of the final part top surface near the overhang and the variation of surface finish on the down-facing surfaces. Ultimately, the improvements to the in-situ process monitoring and part qualities demonstrate the utility and future potential tuning and optimizing more complex laser scan strategies.
  • Additive Biomanufacturing of Scaffolds for Breast Reconstruction
    • Abstract: Publication date: Available online 4 September 2019Source: Additive ManufacturingAuthor(s): Mina Mohseni, Onur Bas, Nathan J. Castro, Beat Schmutz, Dietmar W. Hutmacher Limitations for the current clinical treatment strategies for breast reconstruction have prompted researchers and bioengineers to develop unique techniques based on tissue engineering and regenerative medicine (TE&RM) principles. Recently, scaffold-guided soft TE has emerged as a promising approach due to its potential to modulate the process of tissue regeneration. Herein, we utilized additive biomanufacturing (ABM) to develop an original design-based concept for scaffolds which can be applied in TE-based breast reconstruction procedures. The scaffold design addresses biomechanical and biological requirements for medium to large-volume regeneration with the potential of customization. The model is composed of two independent structural components. The external structure provides biomechanical stability to minimize load transduction to the newly formed tissue while the internal structure provides a large pore and fully interconnected pore architecture to facilitate tissue regeneration. A methodology was established to design, optimize and 3D print the external structure with customized biomechanical properties. The internal structure was also designed and printed with a gradient of pore size and a channel structure to facilitate lipoaspirated fat delivery and entrapment. A fused filament fabrication-based printing strategy was employed to print two structures as a monolithic breast implant.
  • 3D printed architected hollow sphere foams with low-frequency phononic
           band gaps
    • Abstract: Publication date: Available online 3 September 2019Source: Additive ManufacturingAuthor(s): Olivia McGee, Huan Jiang, Feng Qian, Zian Jia, Lifeng Wang, Han Meng, Dimitrios Chronopoulos, Yanyu Chen, Lei Zuo We experimentally and numerically investigate elastic wave propagation in a class of lightweight architected materials composed of hollow spheres and binders. Elastic wave transmission tests demonstrate the existence of vibration mitigation capability in the proposed architected foams, which is validated against the numerically predicted phononic band gap. We further describe that the phononic band gap properties can be significantly altered through changing hollow sphere thickness and binder size in the architected foams. Importantly, our results indicate that by increasing the stiffness contrast between hollow spheres and binders, the phononic band gaps are broadened and shifted toward a low-frequency range. At the threshold stiffness contrast of 50, the proposed architected foam requires only a volume fraction of 10.8% while exhibiting an omnidirectional band gap size exceeding 130%. The proposed design paradigm and physical mechanisms are robust and applicable to architected foams with other topologies, thus providing new opportunities to design phononic metamaterials for low-frequency vibration control.
  • Direct-write Printed Broadband Inductors
    • Abstract: Publication date: Available online 3 September 2019Source: Additive ManufacturingAuthor(s): Yuan Gu, Donghun Park, Stephen Gonya, Joseph Jendrisak, Siddhartha Das, D.R. Hines The capability to additively manufacture fully-functioning electronic circuits is a frontier in 3D-printed electronics that will afford unprecedented scalability, miniaturization, and conformability of electronic circuits. The printed passives, such as resistors, capacitors, and inductors, however, are rarely capable of performances comparable to that of the commercially available versions. In this paper, we report a novel procedure that employs three-dimensional (3D) additive manufacturing techniques to fabricate high-frequency, tapered-solenoid type inductors for RF applications capable of wide bandwidth performance. The design includes a polymer support structure to reduce the parasitic capacitance between the inductor and the substrate, a tapered solid core, and conducting windings. Each design component is printed using aerosol-jet (AJ) printing methods on a grounded coplanar waveguide such that the small end of the conical-shaped inductor is connected to the transmission line and the base of the inductor is connected to ground. Two types of solid-core inductors were fabricated: one with a printed polymer core and another with a non-printed iron core. Scattering parameter measurements establish that the polymer and iron-core inductors, combined with a 45º-polymer support structure, can achieve usable bandwidths up to 18 GHz and 40 GHz, respectively, with low insertion loss. 3D model and circuit model simulations were also carried out to study inductor performance in terms of self-resonance and insertion loss.
  • Rapid cooling of laser sintered part cakes using airflow through cracks
    • Abstract: Publication date: Available online 29 August 2019Source: Additive ManufacturingAuthor(s): Ryuichi Kobayashi, Yuki Yamauchi, Seiji Koganei, Takashi Kigure In polymer laser sintering, the generated part cake is a large mass of powder, and the part cake is heated to nearly its melting point. Accelerating this cooling process would allow the quick harvesting of the parts. Here we propose a method that promotes the cooling of the part cake using injected air into the cracks formed inside the part cake. Further, a system was designed and experimentally tested to inject air into the bottom of the fabricated part cake. The results denoted that the internal temperature of the part cake reached the glass transition point 17 hours earlier than it did by natural cooling without airflow. Furthermore, the airflow did not result in any significant deformation or adversely affect the mechanical properties of parts. In addition, the heat transfer coefficient of the crack was estimated using the finite element method and was used to evaluate the cooling enhancement limit based on a parametric study. Thus, we concluded that the airflow through the cracks facilitated the rapid cooling of the part cakes, reducing the production time required for polymer laser sintering.
  • Design and Additive Manufacture of Functionally Graded Structures Based on
           Digital Materials
    • Abstract: Publication date: Available online 29 August 2019Source: Additive ManufacturingAuthor(s): Inigo FloresABSTRACTVoxel-based multimaterial jetting additive manufacturing allows fabrication of digital materials (DMs) at meso-scale (˜1 mm) by controlling the deposition patterns of soft elastomeric and rigid glassy polymers at the voxel-scale (˜90 μm). The digital materials can then be used to create heterogeneous functionally graded material (FGM) structures at macro-scale (˜10 mm) programmed to behave in a predefined manner. This offers huge potential for design and fabrication of novel and complex bespoke mechanical structures.This paper presents a complete design and manufacturing workflow that simultaneously integrates material design, structural design, and product fabrication of FGM structures based on digital materials. This is enabled by a regression analysis of the experimental data on mechanical performance of the DMs i.e., Young’s modulus, tensile strength and elongation at break. This allows us to express the material behavior simply as a function of the microstructural descriptors (in this case, just volume fraction) without having to understand the underlying microstructural mechanics while simultaneously connecting it to the process parameters.Our proposed design and manufacturing approach is then demonstrated and validated in two series of design exercises to devise complex FGM structures. First, we design, computationally predict and experimentally validate the behavior of prescribed designs of FGM tensile structures with different material gradients. Second, we present a design automation approach for optimal FGM structures. The comparison between the simulations and the experiments with the FGM structures shows that the presented design and fabrication workflow based on our modeling approach for DMs at meso-scale can be effectively used to design and predict the performance of FGMs at macro-scale.Graphical Graphical abstract for this article
  • Real-time feedback controlled conversion in vat photopolymerization of
           ceramics: a proof of principle
    • Abstract: Publication date: Available online 8 July 2019Source: Additive ManufacturingAuthor(s): Thomas Hafkamp, Gregor van Baars, Bram de Jager, Pascal Etman Technical ceramics for high-performance applications can be additively manufactured using vat photopolymerization technology. This technology faces two main challenges: increasing ceramic product size and improving product quality. The integration of process control strategies into AM equipment is expected to play a key role in tackling these challenges. This work demonstrates the feasibility of real-time and in-situ feedback control of the light-initiated polymerization reaction that lies at the core of vat photopolymerization technology. To prove the principle, a single-layer experimental setup was developed in which the degree of conversion was measured by infrared spectroscopy. Experimental data obtained from this setup was used to develop a control-oriented process model and identify its parameters. A material perturbation was applied by adding an inhibitor and the case with and without feedback control were compared. The results show that the feedback controller successfully compensated for the material perturbation and reached the same final conversion value as the unperturbed case. This result can be considered a fundamental step towards additive manufacturing of defect-free ceramic parts using in-line process control.Graphical abstractGraphical abstract for this article
  • High-power laser-matter interaction during laser powder bed fusion
    • Abstract: Publication date: Available online 3 July 2019Source: Additive ManufacturingAuthor(s): Jie Yin, Langliang Yang, Xu Yang, Haihong Zhu, Dengzhi Wang, Linda Ke, Zemin Wang, Guoqing Wang, Xiaoyan Zeng Laser powder bed fusion (LPBF) additive manufacturing (AM) is developing with the goal of fabricating parts with high performance and high efficiency. Laser power is the key factor to the efficiency, microstructure and performance in LPBF. However, there are limited reports regarding the laser-matter interaction in LPBF under high-power conditions. In this work, the molten pool characteristics and spatter behavior in LPBF with a high power and a wide process window (from 350 W to 1550 W) are studied based on high-speed high-resolution imaging. The results show that the molten pool characteristics and spatter behavior depend on the laser input energy. The average ejection velocity and ejection angle increase with the laser power. The droplet column ejection and large spatters are prone to occur with a high-power laser. Furthermore, the times at which the vapor depression and the protrusion in the molten pool first occur decrease dramatically with an increase in the laser input energy. When the laser mode and spot size are kept constant, the laser power determines the amount of time required for melting, the vapor depression and the protrusion in LPBF to occur, while the laser scan velocity determines whether the laser dwell time is sufficient for these phenomena to form.
  • Impact behavior and fractography of additively manufactured polymers:
           Laser sintering, multijet fusion, and hot lithography
    • Abstract: Publication date: October 2019Source: Additive Manufacturing, Volume 29Author(s): David Tasch, Martin Schagerl, Benjamin Wazel, Gernot Wallner To reduce the lead time, polymer fuel tanks could be toollessly produced using additive manufacturing (AM) technologies. Detailed knowledge of the performance of AM polymers is essential for the design and development of such components. In instrumented static (0.01 mm/s) and dynamic (2.5 m/s) three-point bending and puncture tests, the impact behaviors of polyamide and methacrylate-based photopolymer test specimens were compared. The polyamide test specimens were produced by laser sintering and multijet fusion, and the photopolymer test specimens were produced by a hot lithography process. Fractography was performed using stereo light and scanning electron microscopy to investigate the fracture surface morphology. The test results were used to analyze the relationships among the surface roughness, shear modulus, and glass transition temperature. The AM polymers revealed comparable force–displacement behaviors in a static three-point bending test, but their impact behaviors differed greatly. The obtained results highlight that the impact performance of AM polymers is an essential design variable for fluid-containing parts.
  • Thermal analysis of wire-based direct energy deposition of Al-Mg using
           different laser irradiances
    • Abstract: Publication date: October 2019Source: Additive Manufacturing, Volume 29Author(s): M. Froend, V. Ventzke, N. Kashaev, B. Klusemann, J. Enz The wire-based direct energy deposition of metallic lightweight materials such as titanium or aluminium alloys has recently received increasing attention in industry and academia. However, high-throughput deposition is mostly associated with process-limiting phenomena such as the development of high temperatures resulting in poor surface quality as well as coarse and unidirectional solidification microstructures. In this regard, laser systems, which are already widely used in industrial processes, allow for a great variety in the controllability of energy inputs, thereby enabling the control of process temperatures and resulting microstructures. The subject of the current study is the detailed elucidation and evaluation of important features such as the development of temperature gradients, resulting cooling rates and thermal cycles for different laser beam irradiances. Significant heat accumulation and process instabilities as well as inhomogeneous thermal profiles along the length and height of the parts were observed at a high laser beam irradiance. In contrast, lower laser beam irradiance resulted in a more stable process with increased cooling rates, which favourably influenced the refinement of the solidification microstructure.
  • High-fidelity 3D Printing using Flashing Photopolymerization
    • Abstract: Publication date: Available online 19 August 2019Source: Additive ManufacturingAuthor(s): Shangting You, Pengrui Wang, Jacob Schimelman, Henry H. Hwang, Shaochen Chen Photopolymerization-based 3D printing has emerged as a promising technique to fabricate 3D structures. However, during the printing process, polymerized materials such as hydrogels often become highly light-scattering, thus perturbing incident light distribution and thereby deteriorating the final print resolution. To overcome this scattering-induced resolution deterioration, we developed a novel method termed flashing photopolymerization (FPP). Our FPP approach is informed by the fundamental kinetics of photopolymerization reactions, where light exposure is delivered in millisecond-scale ‘flashes’, as opposed to continuous light exposure. During the period of flash exposure, the prepolymer material negligibly scatters light. The material then polymerizes and opacifies in absence of light, therefore the exposure pattern is not perturbed by scattering. Compared to the conventional use of a continuous wave (CW) light source, the FPP fabrication resolution is improved. FPP also shows little dependency on the exposure, thus minimizing trial-and-error type optimization. Using FPP, we demonstrate its use in generating high-fidelity 3D printed constructs.
  • Processing of Gas-nitrided AISI 316L Steel Powder by Laser Powder Bed
           Fusion – Microstructure and Properties
    • Abstract: Publication date: Available online 19 August 2019Source: Additive ManufacturingAuthor(s): J. Boes, A. Röttger, L. Becker, W. Theisen This work investigated the processing of high nitrogen-alloyed austenitic stainless steels by laser powder bed fusion (L-PBF). Prior to L-PBF processing, the AISI 316 L steel powder was nitrided at a temperature of 675° in a 3 bar nitrogen atmosphere, thus achieving a N content of 0.58 mass-%. By mixing nitrided 316 L powder with untreated 316 L powder, two different powder mixtures were obtained with 0.065 mass-% and 0.27 mass-% nitrogen, respectively. After nitriding and mixing, the powder was characterized in terms of its flow properties and chemical composition. The nitrided steel powder was then processed by L-PBF, and the microstructure as well as the chemical composition were investigated by means of scanning electron microscopy and carrier gas hot extraction. It was shown that nitriding of steel powders in an N2 atmosphere can be used to significantly increase the nitrogen content of the powder without impairing its flow properties. With increasing nitrogen content of the powder, the porosity within the L-PBF built specimens increased. However, both the yield strength and the tensile strength were greatly improved without a marked reduction in the elongation at fracture of the respective steels. This work shows that nitrogen-alloyed austenitic stainless steels can be processed by L-PBF and the mechanical properties can be improved.
  • Keyhole-induced porosities in Laser-based Powder Bed Fusion (L-PBF) of
           Ti6Al4V: High-fidelity modelling and experimental validation
    • Abstract: Publication date: Available online 17 August 2019Source: Additive ManufacturingAuthor(s): Mohamad Bayat, Aditi Thanki, Sankhya Mohanty, Ann Witvrouw, Shoufeng Yang, Jesper Thorborg, Niels Skat Tiedje, Jesper Henri Hattel Metal additive manufacturing, despite of offering unique capabilities e.g. unlimited design freedom, short manufacturing time, etc., suffers from raft of intrinsic defects. Porosity is of the defects which can badly deteriorate a part’s performance. In this respect, enabling one to observe and predict the porosity during this process is of high importance. To this end, in this work a combined numerical and experimental approach has been used to analyze the formation, evolution and disappearance of keyhole and keyhole-induced porosities along with their initiating mechanisms, during single track L-PBF of a Ti6Al4V alloy. In this respect, a high-fidelity numerical model based on the Finite Volume Method (FVM) and accomplished in the commercial software Flow-3D is developed. The model accounts for the major physics taking place during the laser-scanning step of the L-PBF process. To better simulate the actual laser-material interaction, multiple reflection with the ray-tracing method has been implemented along with the Fresnel absorption function. The results show that during the keyhole regime, the heating rises dramatically compared to the shallow-depth melt pool regime due to the large entrapment of laser rays in the keyhole cavities. Also a detailed parametric study is performed to investigate the effect of input power on thermal absorptivity, heat transfer and melt pool anatomy. Furthermore, an X-ray Computed Tomography (X-CT) analysis is carried out to visualize the pores formed during the L-PBF process. It is shown, that the predicted shape, size and depth of the pores are in very good agreement with those found by either X-CT or optical and 3D digital microscopic images.
  • Improving the filament weld-strength of fused filament fabrication
           products through improved interdiffusion
    • Abstract: Publication date: October 2019Source: Additive Manufacturing, Volume 29Author(s): Yee Song Ko, Denis Herrmann, Oliver Tolar, Wilfried J. Elspass, Christof Brändli Fused Filament Fabrication (FFF) is a popular additive manufacturing technique where molten polymer filament is applied in a raster pattern, layer by layer, to obtain the work piece. A necessary consequence of this method is a pronounced mechanical anisotropy of the product; the interface between the filaments is weaker compared to the filament itself. The strength of this interface is governed by the reptation theory which postulates a more efficient interpenetration of polymeric surfaces with decreasing polymer viscosity. This relationship was utilized in this work to modify a polycarbonate-acrylonitrile butadiene styrene polymer blend to produce FFF work pieces with less mechanical anisotropy, independent of printer settings. The tensile strength ratio of the printed interface to bulk tensile strength could be increased from 41% to 95%. Though the absolute bulk tensile strength decreases slightly, this method presents an easy and effective way to address the mechanical problems inherent in the FFF-method.Graphical abstractGraphical abstract for this article
  • 3D printed thermoplastic polyurethane bladder for manufacturing of fiber
           reinforced composites
    • Abstract: Publication date: October 2019Source: Additive Manufacturing, Volume 29Author(s): Garam Kim, Eduardo Barocio, R. Byron Pipes, Ronald Sterkenburg The Bladder Assisted Composite Manufacturing (BACM) technique allows fabrication of complex hollow composite geometries. However, traditional bladder manufacturing methods require multiple steps and a master geometry which increases the cost and the manufacturing time. Hence, additively manufactured bladders are presented as an alternative solution to bladders manufactured through traditional methods. The use of printed bladders is demonstrated by consolidating and curing a composite part made out of an aerospace grade composite prepreg material, IM7/8552. Bladders are additively manufactured using the Fused Deposition Modeling (FDM) technique with Thermoplastic Polyurethane (TPU). Based on the results of a thermomechanical investigation of the TPU, a two-step curing cycle for manufacturing a composite part with IM7/8552 prepreg was designed. The part consolidation achieved with this method was characterized by measuring void content and comparing it to the void content in a sample cured in a standard autoclave process. The low void content achieved with the BACM method demonstrated the potential of this technology for providing bladders for short production runs or prototyping.
  • An investigation into specimen property to part performance relationships
           for laser beam powder bed fusion additive manufacturing
    • Abstract: Publication date: October 2019Source: Additive Manufacturing, Volume 29Author(s): Rakish Shrestha, Nima Shamsaei, Mohsen Seifi, Nam Phan The influence of part size and geometry on the melt pool size, microstructural features, and resulting mechanical properties of additive manufactured 17-4 precipitation hardening (PH) stainless steel (SS), fabricated using a laser beam powder bed fusion (LB-PBF) process is investigated. Three different types of geometries including a dog-bone part (i.e. representing the specimen or the witness coupon) and two square rods with different cross-sectional sizes (i.e. representing the parts) were designed and fabricated using the same set of process parameters. Mechanical properties were determined under quasi-static tensile and uniaxial strain-controlled fully-reversed fatigue loading conditions. Experimental results confirmed a minimal effect of part geometry on the tensile behavior of the LB-PBF 17-4 PH SS as the yield strength ranged from 1145 to 1198 MPa and ultimate tensile strength varied from 1171 to 1231 MPa. On the other hand, part geometry had a significant impact on the fatigue behavior in the high cycle regime. Specimens fabricated from the large square blocks contained the lowest amount of porosity, and consequently, exhibited the highest fatigue resistance. On the contrary, the highest amount of porosity was observed in the specimens fabricated from the dog-bone parts resulting in an inferior fatigue resistance as compared to other geometries. Microstructural analysis was performed to estimate the effect of part geometry on the thermal history experienced during manufacturing by measuring the melt pool dimensions. Some effects of geometry on the melt pool dimensions were observed as the melt pool depth was found to be shorter for dog-bone specimens and longer for large block specimens. The less elongated melt pools in dog-bone specimens can be attributed to higher cooling rate experienced by the specimens resulting in more entrapped gas pores.Graphical abstractGraphical abstract for this article
  • Motion planning and numerical simulation of material deposition at corners
           in extrusion additive manufacturing
    • Abstract: Publication date: October 2019Source: Additive Manufacturing, Volume 29Author(s): Raphaël Comminal, Marcin P. Serdeczny, David B. Pedersen, Jon Spangenberg The material deposition along a toolpath with a sharp corner is simulated with a computational fluid dynamics model. We investigate the effects of smoothing the toolpath and material over-extrusion on the corner rounding and the corner swelling, for 90° and 30° turns. The toolpath motion is controlled with trapezoidal velocity profiles constrained by a maximal acceleration. The toolpath smoothing of the corner is parametrized by a blending acceleration factor. Analytical solutions for the deviation of the smoothed toolpath from the trajectory of the sharp corner, as well as the additional printing time required by the deceleration and acceleration phases in the vicinity of the turn are provided. Moreover, several scenarios with different blending acceleration factors are simulated, for the cases of a constant extrusion rate and an extrusion rate proportional to the printing head speed. The constant extrusion rate causes material over-extrusion during the deceleration and acceleration phases of the printing head. However, the toolpath smoothing reduces the corner swelling. The amount of underfill and overfill at the inside and outside of the corner are quantified, as compared to an ideal case where the printing head would instantaneously change its speed direction at the corner. The numerical results show that there is an optimal amount of toolpath smoothing where the over-extrusion compensates for the corner rounding; hence improving the quality of the corner. A uniform road width is obtained with the proportional extrusion rate.Graphical abstractGraphical abstract for this article
  • Mechanical and Corrosion Properties of Additively Manufactured CoCrFeMnNi
           High Entropy Alloy
    • Abstract: Publication date: Available online 12 August 2019Source: Additive ManufacturingAuthor(s): Michael A. Melia, Jay D. Carroll, Shaun R. Whetten, Saba N. Esmaeely, Jenifer Locke, Emma White, Iver Anderson, Michael Chandross, Joseph R. Michael, Nicolas Argibay, Eric J. Schindelholz, Andrew B. Kustas This study investigates the mechanical and corrosion properties of as-built and annealed equi-atomic CoCrFeMnNi alloy produced by laser-based directed energy deposition (DED)Additive Manufacturing (AM). The high cooling rates of DED produced a single-phase, cellular microstructure with cells on the order of 4 µm in diameter and inter-cellular regions that were enriched in Mn and Ni. Annealing created a chemically homogeneous recrystallized microstructure with a high density of annealing twins. The average yield strength of the as-built condition was 424 MPa and exceeded the annealed condition (232 MPa), however; the strain hardening rate was lower for the as-built material stemming from higher dislocation density associated with DED parts and the fine cell size. In general, the yield strength, ultimate tensile strength, and elongation-to-failure for the as-built material exceeded values from previous studies that explored other AM techniques to produce the CoCrFeMnNi alloy. Ductile fracture occurred for all specimens with dimple initiation associated with nanoscale oxide inclusions. The breakdown potential (onset of pitting corrosion) was similar for the as-built and annealed conditions at 0.40 VAg/AgCl when immersed in 0.6 M NaCl. Pit morphology/propagation for the as-built condition exhibited preferential corrosion of inter-cellular Ni/Mn regions leading to a tortuous pit bottom and cover, while the annealed conditions pits resembled lacy pits similar to 304 L steel. A passive oxide film depleted in Cr cations with substantial incorporation of Mn cations is proposed as the primary mechanism for local corrosion susceptibility of the CoCrFeMnNi alloy.Graphical abstractGraphical abstract for this article
  • Residual stresses and distortion in the patterned printing of titanium and
           nickel alloys
    • Abstract: Publication date: October 2019Source: Additive Manufacturing, Volume 29Author(s): Qianru Wu, Tuhin Mukherjee, Changmeng Liu, Jiping Lu, Tarasankar DebRoy Since the deposition patterns affect the stresses and distortions, we examined their effects on multi-layer wire arc additive manufacturing (WAAM) of Ti-6Al-4V and Inconel 718 components experimentally and theoretically. We measured residual stresses by hole drilling method in three identical components printed using different deposition patterns. In order to understand the origin and the temporal evolution of residual stresses and distortion, we used a well-tested thermo-mechanical model after validating the computed results with experimental data for different deposition patterns. Distortions were also examined based on non-dimensional analysis.We show that printing with short track lengths can minimize residual stresses and distortion among the three patterns investigated for both alloys. Both Ti-6Al-4V and Inconel 718 had similar fusion zone shape and size and were equally susceptible to deformation and warping, although Ti-6Al-4V was relatively less vulnerable to delamination due to its higher yield strength. A dimensionless strain parameter accurately predicted the effects of WAAM parameters on distortion and this approach is especially useful when the detailed thermo-mechanical calculations cannot be undertaken.
  • Ultra-high strength martensitic 420 stainless steel with high ductility
    • Abstract: Publication date: October 2019Source: Additive Manufacturing, Volume 29Author(s): Kamran Saeidi, Daniel Leon Zapata, Frantisek Lofaj, Lenka Kvetkova, Jon Olsen, Zhijian Shen, Farid Akhtar Martensitic 420 stainless steel was successfully fabricated by Selective laser melting (SLM) with>99% relative density and high mechanical strength of 1670 MPa, yield strength of 600 MPa and elongation of 3.5%. X-ray diffraction (XRD) and scanning electron microscopy disclosed that the microstructure of SLM 420 consisted of colonies of 0.5–1 μm sized cells and submicron martensitic needles with 11 wt. % austenite. Tempering of as-built SLM 420 stainless steel at 400 °C resulted in ultra-high strength material with high ductility. Ultimate tensile strength of 1800 MPa and yield strength of 1400 MPa were recorded with an elongation of 25%. Phase transformation analysis was carried out using Rietveld refinement of XRD data and electron backscattered diffraction (EBSD), which showed the transformation of martensite to austenite, and resulted in austenite content of 36 wt. % in tempered SLM 420 stainless steel. Transformation induced plasticity (TRIP), austenite formation and fine cellular substructure along with sub-micron martensite needles resulted in stainless steel with high tensile strength and ductility. The advanced mechanical properties were compared with conventionally made ultra-high-strength steels, and the microstructure-properties relationships were disclosed.
  • Cavitation erosion resistance of 316L austenitic steel processed by
           selective laser melting (SLM)
    • Abstract: Publication date: October 2019Source: Additive Manufacturing, Volume 29Author(s): C. Hardes, F. Pöhl, A. Röttger, M. Thiele, W. Theisen, C. Esen Every SLM-fabricated component typically possesses a process-specific microstructure that fundamentally differs from any conventionally fabricated specimen. This publication addresses the evaluation of microstructure-related influencing factors on the resistance against cavitation erosion. We exemplarily compared the findings to a cast and hot rolled reference sample. Due to careful adjustment of the process parameters, the overall cavitation erosion resistance of both SLM-processed and conventionally fabricated 316L are very much alike in the investigated case. The incubation period of intact surface areas is improved by the greater hardness and yield strength of the SLM specimen, which is attributable to an increased dislocation density and a smaller grain size. Nevertheless, processing and powder feeding during SLM-fabrication occasionally results in microstructural defects, at which pronounced mass loss during cavitation was registered. X-ray measurements of the residual stresses reveal the development of severe compressive stresses that emerge after a few seconds of cavitation. This compressive stress state delays the immediate propagation of SLM-inherent micro cracks. Moreover, investigations of the microstructure in combination with examination of the ongoing surface deformation highlighted the emergence of coarse grains that grew towards the temperature gradient. This effect leads to a temporarily high surface roughness, local stress concentrations and an increased probability of cavitation impacts. Furthermore, parallel cracks appear perpendicular to the scan tracks that are traced back to formerly protruded slip bands.
  • Non-destructive testing for wire + arc additive manufacturing of aluminium
    • Abstract: Publication date: October 2019Source: Additive Manufacturing, Volume 29Author(s): João B. Bento, Ana Lopez, Inês Pires, Luísa Quintino, Telmo G. Santos Wire + Arc Additive Manufacturing (WAAM) has already proven to be successful for the production of large metal parts. However, there are still no specific standards available to label the quality requirements of the parts produced by WAAM and this is preventing a more widespread adoption of the technique.A crucial step towards the quality assurance of WAAM parts will be the development of Non-Destructive Testing (NDT) systems capable of identifying defects while parts are being produced. In this regard, Eddy Current Testing (ECT) can play a significant role, by allowing the inspection of both ferromagnetic and non-ferromagnetic materials, with high speeds and without contact with the material surface. The limitation here is that commercial ECT targets only the inspection of surface and subsurface defects.This study is focused on the development of a NDT system which includes customized ECT probes for the inline layer-by-layer detection of defects in aluminium WAAM samples. Results revealed that the developed EC probes were able to locate artificial defects: at depths up to 5 mm; with a thickness as small as 350 μm; with the probe up to 5 mm away from the inspected sample surface.The developed ECT probes proved to surpass the limitation of commercial ones. Also, these probes were able to overcome the limitations caused by the surface roughness of the samples and the high temperatures involved in the deposition process. These preliminary results represent an important step for the development of NDT systems for WAAM.
  • Ultrasonic material dispensing-based selective laser melting for 3D
           printing of metallic components and the effect of powder compression
    • Abstract: Publication date: October 2019Source: Additive Manufacturing, Volume 29Author(s): Chao Wei, Heng Gu, Zhe Sun, Dongxu Cheng, Yuan-Hui Chueh, Xiaoji Zhang, Yihe Huang, Lin Li Selective laser melting (SLM) is one of the most commonly used metallic component 3D printing techniques. In a previous investigation of multiple materials SLM reported by The University of Manchester, high porosities and cracks were found in the regions where the powder was deposited via an ultrasonic powder dispenser. The low powder packing density was identified as a critical reason for this. In this paper, we report a new method to compress the ultrasonically deposited powder layer in order to increase the powder packing density. The effects of powder deposition velocity, powder track overlap distance and powder compression force on the deposited powder characteristics were investigated. The microstructure, tensile strengths, and porosity of the laser-fused samples were analyzed. The results indicated that powder compression could reduce porosity and component distortion and increase the mechanical strength of the printed parts.
  • Benchmarking Spatial Resolution in Electronic Imaging for Potential
           In-Situ Electron Beam Melting Monitoring
    • Abstract: Publication date: Available online 10 August 2019Source: Additive ManufacturingAuthor(s): Hay Wong, Derek Neary, Eric Jones, Peter Fox, Chris Sutcliffe Electron Beam Melting (EBM) is an increasingly used Additive Manufacturing (AM) technique employed by many industrial sectors, including the medical device and aerospace industries. In-process EBM monitoring for quality assurance purposes has been a popular research area. Electronic imaging has recently been investigated as one of the in-process EBM data collection methods, alongside thermal / optical imaging techniques. So far, the disseminations focus on the design of an electronic imaging system and the ability to generate electronic images in-process, experiments are yet to be carried out to benchmark one of the most important features of any imaging systems – spatial resolution. This article addresses this knowledge gap by: (1) proposing an indicator for the estimation of spatial resolution which includes the Backscattered Electrons (BSE) information depth, (2) estimating the achievable spatial resolution when electronic imaging is carried out inside an Arcam A1 EBM machine, and (3) presenting an experimental method to conduct a knife edge test with the EBM machine. Analyses of experimental results indicated that the spatial resolution was of the order of 0.3 to 0.4 mm when electronic imaging was carried out at room temperature. It is believed that by disseminating an analysis and experimental method to estimate and quantify spatial resolution, this study has contributed to the on-going quality assessment research in the field of in-process monitoring of the EBM process.
    • Abstract: Publication date: Available online 9 August 2019Source: Additive ManufacturingAuthor(s): Thao Phan Thi Phuong Material Extrusion (ME) is a type of Additive Manufacturing (AM) process that creates parts by depositing polymer filaments in successive layers. The strength of ME products depends on both the cohesive strength between layers and between rasters. The raster gap is the most significant process factor affecting the strength of ME built parts. Standard tensile tests with a dog-bone shaped specimens are not suitable to determine the strength between layers of the ME built parts. A new model is introduced to predict the cohesive strength between layers using the true area of contact which can be obtained from the apparent values taken from mini three-point bending tests. The accuracy of the introduced model was verified by comparing its bending test results with different build parameters, the applicability and promise of the introduced model were confirmed.Graphical abstractGraphical abstract for this article
  • Shape retention and infiltration height in complex WC-Co parts made via
           binder jet of WC with subsequent Co melt infiltration
    • Abstract: Publication date: Available online 8 August 2019Source: Additive ManufacturingAuthor(s): Corson L. Cramer, Natalie R. Wieber, Trevor G. Aguirre, Richard A. Lowden, Amy M. Elliott Additive manufacturing (AM) of complex tungsten carbide-cobalt (WC-Co) parts was achieved using binder jet additive manufacturing (BJAM) of WC powders followed by Co infiltration. The intent of the study is to explore the shape retention, infiltration height, and properties of parts made with this method. Using BJAM with infiltration of the metal phase can limit shrinkage and grain growth in ceramic-metal (cermet) composites compared to other additive manufacturing (AM) methods. Knowledge of previous infiltration studies was used to help process parts to imitate production of parts. The properties such as density, microstructure, grain size, and hardness of the parts are characterized along the infiltration height. Fracture toughness is measured where applicable. This approach has the potential to achieve highly dense WC-Co parts that are net-shaped with some ternary phase and z-direction distortion.
  • 3D Printing Using Powder Melt Extrusion
    • Abstract: Publication date: Available online 6 August 2019Source: Additive ManufacturingAuthor(s): Bret M. Boyle, Panupoan T. Xiong, Tara E. Mensch, Timothy J. Werder, Garret M. Miyake Additive manufacturing promises to revolutionize manufacturing industries. However, 3D printing of novel build materials is currently limited by constraints inherent to printer designs. In this work, a bench-top powder melt extrusion (PME) 3D printer head was designed and fabricated to print parts directly from powder-based materials rather than filament. The final design of the PME printer head evolved from the Rich Rap Universal Pellet Extruder (RRUPE) design and was realized through an iterative approach. The PME printer was made possible by modifications to the funnel shape, pressure applied to the extrudate by the auger, and hot end structure. Through comparison of parts printed with the PME printer with those from a commercially available fused filament fabrication (FFF) 3D printer using common thermoplastic poly(lactide) (PLA), high impact poly(styrene) (HIPS), and acrylonitrile butadiene styrene (ABS) powders (< 1 mm in diameter), evaluation of the printer performance was performed. For each build material, the PME printed objects show comparable viscoelastic properties by dynamic mechanical analysis (DMA) to those of the FFF objects. However, due to a significant difference in printer resolution between PME (X-Y resolution of 0.8 mm and a Z-layer height calibrated to 0.1 mm) and FFF (X-Y resolution of 0.4 mm and a Z-layer height of 0.18 mm), as well as, an inherently more inconsistent feed of build material for PME than FFF, the resulting print quality, determined by a dimensional analysis and surface roughness comparisons, of the PME printed objects was lower than that of the FFF printed parts based on the print layer uniformity and structure. Further, due to the poorer print resolution and inherent inconsistent build material feed of the PME, the bulk tensile strength and Young’s moduli of the objects printed by PME were lower and more inconsistent (49.2 ± 10.7 MPa and 1620 ± 375 MPa, respectively) than those of FFF printed objects (57.7 ± 2.31 MPa and 2160 ± 179 MPa, respectively). Nevertheless, PME print methods promise an opportunity to provide a platform on which it is possible to rapidly prototype a myriad of thermoplastic materials for 3D printing.Graphical abstractGraphical abstract for this article
  • Effects of Amylose Content on the Mechanical Properties of
           Starch-Hydroxyapatite 3D Printed Bone Scaffolds
    • Abstract: Publication date: Available online 6 August 2019Source: Additive ManufacturingAuthor(s): Caitlin Koski, Susmita Bose Recent efforts in the bone and tissue engineering field have been made to create resorbable bone scaffolds that mimic the structure and function of natural bone. While enhancing mechanical strength through increased ceramics loading has been shown for sintered parts, few studies have reported that the crosslinked polymer provides strength for the composite parts without post processing. The objective of this study is to assess the effect of amylose content on the mechanical and physical properties of starch-hydroxyapatite (HA) composite scaffolds for bone and tissue engineering applications. Starch-HA composite scaffolds utilizing corn, potato, and cassava sources of gelatinized starch were fabricated through the utilization of a self-designed and built solid freeform fabricator (SFF). It was hypothesized that the mechanical strength of the starch-HA scaffolds would increase with increasing amylose content based on the botanical source and weight percentage added. Overall, compressive strengths of scaffolds were achieved up to 12.49 + 0.22 MPa, through the implementation of 5.46 wt% corn starch with a total amylose content of 1.37%. The authors propose a reinforcement mechanism through a matrix of gelled starch particles and interlocking of hydroxyl-rich amylose with hydroxyapatite through hydrogen bonding. XRD, FTIR, and FESEM were utilized to further characterize these scaffold structures, ultimately elucidating amylose as a biologically relevant reinforcement phase of resorbable bone scaffolds.Graphical Graphical abstract for this article
  • Melt Pool Geometry and Morphology Variability for the Inconel 718 Alloy in
           a Laser Powder Bed Fusion Additive Manufacturing Process
    • Abstract: Publication date: Available online 6 August 2019Source: Additive ManufacturingAuthor(s): Luke Scime, Jack Beuth Expanding on prior process mapping work by the authors, multiple melt pool cross-sections are measured at multiple process parameter combinations for the Inconel 718 alloy in a Laser Powder Bed Fusion (L-PBF) process. Collection of such data enables the study of the variability of melt pool geometry (e.g. width, depth, and cross-sectional area) across process space. Furthermore, the statistical distribution of the measured melt pool geometries is compared to that of an equivalent normal distribution and intriguing outliers are observed. The cross-sectional morphology of the melt pools are associated with defects such as keyholing porosity and balling and the variability of the defects is quantified. The final product of this work is a robust description of L-PBF In718 melt pool behavior, based on ex-situ observations, which can be linked to in-situ observations of melt pool morphology in future work.
  • Electrical resistivity of pure copper processed by medium-powered laser
           powder bed fusion additive manufacturing for use in electromagnetic
    • Abstract: Publication date: Available online 6 August 2019Source: Additive ManufacturingAuthor(s): Cassidy Silbernagel, Leonidas Gargalis, Ian Ashcroft, Richard Hague, Michael Galea, Phill Dickens Pure copper is an excellent thermal and electrical conductor, however, attempts to process it with additive manufacturing (AM) technologies have seen various levels of success. While electron beam melting (EBM) has successfully processed pure copper to high densities, laser powder bed fusion (LPBF) has had difficulties achieving the same results without the use of very high power lasers. This requirement has hampered the exploration of using LPBF with pure copper as most machines are equipped with lasers that have low to medium laser power densities. In this work, experiments were conducted to process pure copper with a 200 W LPBF machine with a small laser spot diameter resulting in an above average laser power density in order to maximise density and achieve low electrical resistivity. The effects of initial build orientation and post heat treatment were also investigated to explore their influence on electrical resistivity. It was found that despite issues with high porosity, heat treated specimens had a lower electrical resistivity than other common AM materials such as the aluminium alloy AlSi10Mg. By conducting these tests, it was found that despite having approximately double the resistivity of commercially pure copper, the resistivity was sufficiently low enough to demonstrate the potential to use AM to process copper suitable for electrical applications.Graphical abstractGraphical abstract for this article
  • Ultrasonic additive manufacturing using feedstock with build-in circuitry
           for 3D metal embedded electronics
    • Abstract: Publication date: October 2019Source: Additive Manufacturing, Volume 29Author(s): Alkaios Bournias-Varotsis, Xiaoxiao Han, Russell A. Harris, Daniel S. Engstrøm Embedded electronics and sensors are becoming increasingly important for the development of Industry 4.0. For small components, space constraints lead to full 3D integration requirements that are only achievable through Additive Manufacturing. Manufacturing metal components usually require high temperatures incompatible with electronics but Ultrasonic Additive Manufacturing (UAM) can produce components with mechanical properties close to bulk, but with the integration of internal embedded electronics, sensors or optics. This paper describes a novel manufacturing route for embedding electronics with 3D via connectors in an aluminium matrix. Metal foils with printed conductors and insulators were prepared separately from the UAM process thereby separating the electronics preparation from the part consolidation. A dual material polymer layer exhibited the best electrically insulating properties, while providing mechanical protection of printed conductive tracks stable up to 100 °C. General design and UAM process recommendations are given for 3D embedded electronics in a metal matrix.
  • Highly Loaded Fiber Filled Polymers for Material Extrusion: A Review of
           Current Understanding
    • Abstract: Publication date: Available online 3 August 2019Source: Additive ManufacturingAuthor(s): Jacob J. Fallon, Steven H. McKnight, Michael J. Bortner This review documents the current state of the art of highly filled (HF) polymer composite systems used in additive manufacturing (AM), with a core focus on short and continuous fiber filled composites for use in material extrusion (MatEx) AM. Current state of the art composite materials systems have been succesfully incorporated into the MatEx process with loading percentages up to approximately 45 vol.%. Further increasing the loading percentage would afford significant mechanical improvements that could enable structural performance, however there are currently a number of limitations that need to be addressed. Viscosity limitations associated with MatEx processing of HF composites originate from the low processing pressure inherent to filament feed MatEx processes. Restrictive hot end nozzle geometries (high volume contractions) increase required processing pressure and potential for nozzle clogging failures. The increased viscosity of the HF composite reduces interlayer contact and adhesion during the printing process, resulting in increased void spacing. Mechanical limitations of HF composites processed using MatEx are also reviewed. Flow induced fiber orientation and its influence on viscosity and mechanical anisotropy are investigated. Fiber breakage as well as strain to break limitations are reviewed. Lastly, the geometric packing limitations of fibers within a circular bound nozzle are reviewed. This review takes an in-depth look at recent advances in addressing these challenges, and discusses opportunities for realizing MatEx processing of HF composite systems with significantly improved performance.
  • A Robust Ink Deposition System for Binder Jetting and Material Jetting
    • Abstract: Publication date: Available online 2 August 2019Source: Additive ManufacturingAuthor(s): Xuechen Shen, Hani E. Naguib The adaptation of inkjet technology for additive manufacturing (AM) enabled the highest standards of print speed and print resolution in the industry. However, inkjet printheads impose strict limitations on ink properties. Ink compositions exhibiting volatility, rehydration, surface tension, chemical stability, abrasiveness, and electrical properties that deviate from printhead specifications shorten its service life. Frequent and complex maintenance procedures are necessary, but replacement is the only solution to declining print quality, accruing heavy maintenance costs. This is especially limiting for AM as part quality and properties are closely dependent on ink composition. We propose an ink deposition system designed for robustness by implementing modular and dedicated components. The system deposits ink in a continuous jet. We find optimal process parameters and evaluate system performance in comparison to inkjet and material extrusion (ME). The system produces line widths between 0.3-0.5mm, indicating print resolution capabilities are comparable to commercial ME systems.
  • Overview: Additive Manufacturing Enabled Accelerated Design of Ni-based
           Alloys for Improved Fatigue Life
    • Abstract: Publication date: October 2019Source: Additive Manufacturing, Volume 29Author(s): S. Shao, M.M. Khonsari, S. Guo, W.J. Meng, N. Li An in-depth overview on an emerging area of the additive-manufacturing-enabled, accelerated design of Ni-based alloys for improved high-cycle and very-high-cycle fatigue life is presented. Existing literature on the subject is critically reviewed, and key knowledge gaps are identified. An efficient life-cycle approach, integrating the model-make-measure-verify strategy in the design of these alloys is introduced and discussed.
  • Multi-material additive manufacturing of polymers and metals using fused
           filament fabrication and electroforming
    • Abstract: Publication date: October 2019Source: Additive Manufacturing, Volume 29Author(s): Ryosuke Matsuzaki, Takuya Kanatani, Akira Todoroki This paper proposes an additive manufacturing method that combines fused filament fabrication (FFF) 3D printing and an electroforming technology to fabricate multi-material structures composed of resin and metal. In this method, an FFF 3D printer prints a resin mold that functions as a structural unit in a multi-material structure and as a sacrificial plastic mold for the addition of the metal material. This sacrificial mold is eventually removed. Electroforming the interior of a printed resin mold enables the fabrication of multi-material structures using resin and metal materials. The fabrication conditions for multi-material structures when using the proposed method were investigated and the surfaces of the resulting structures were evaluated. The fabrication conditions for the specified thickness per process and the total thicknesses from all the processes were determined. Furthermore, our results indicated that the shape of the side of the metal portion depended on the forming precision of the FFF 3D printer. We present an example of the fabrication of a gear shape from resin and metal.
  • Generation of Polyphenylene Sulfide Reinforced with a Thermotropic Liquid
           Crystalline Polymer for Application in Fused Filament Fabrication
    • Abstract: Publication date: October 2019Source: Additive Manufacturing, Volume 29Author(s): Mubashir Q. Ansari, Michael J. Bortner, Donald G. Baird In this work, polyphenylene sulfide (PPS) was reinforced with a thermotropic liquid crystalline polymer (TLCP) to generate composite filaments for use in Fused Filament Fabrication (FFF). Because of non-overlapping processing temperatures, rheology enabled taking the advantage of the dual extrusion technology, which generated nearly continuously reinforced filaments that exhibited a tensile strength and modulus of 155.0 ± 24.2 MPa and 40.4 ± 7.5 GPa, respectively. On printing using these filaments, the maximum tensile strength and modulus obtained were 108.5 ± 19.4 MPa and 25.9 ± 1.1 GPa, respectively, higher than the properties reported on using short fiber composites. Moreover, the tensile strength was lower, and the tensile modulus was higher in comparison with the reported use of continuous fibers. Additionally, the tensile properties in the print direction were higher than those of compression molded samples. The nearly continuous reinforcement did not restrict the mobility of the printer, unlike the reported performance of the continuously reinforced carbon fiber thermoplastics in FFF.
  • Austenite reversion kinetics and stability during tempering of an
           additively manufactured maraging 300 steel
    • Abstract: Publication date: October 2019Source: Additive Manufacturing, Volume 29Author(s): F.F. Conde, J.D. Escobar, J.P. Oliveira, A.L. Jardini, W.W. Bose Filho, J.A. Avila Reverted austenite is a metastable phase that can be used in maraging steels to increase ductility via transformation-induced plasticity or TRIP effect. In the present study, 18Ni maraging steel samples were built by selective laser melting, homogenized at 820 °C and then subjected to different isothermal tempering cycles aiming for martensite-to-austenite reversion. Thermodynamic simulations were used to estimate the inter-critical austenite + ferrite field and to interpret the results obtained after tempering. In-situ synchrotron X-ray diffraction was performed during the heating, soaking and cooling of the samples to characterize the martensite-to-austenite reversion kinetics and the reverted austenite stability upon cooling to room temperature. The reverted austenite size and distribution were measured by Electron Backscattered Diffraction. Results showed that the selected soaking temperatures of 610 °C and 650 °C promoted significant and gradual martensite-to-austenite reversion with high thermal stability. Tempering at 690 °C caused massive and complete austenitization, resulting in low austenite stability upon cooling due to compositional homogenization.
  • Laser additive manufacturing of carbon nanotubes (CNTs) reinforced
           aluminum matrix nanocomposites: Processing optimization, microstructure
           evolution and mechanical properties
    • Abstract: Publication date: October 2019Source: Additive Manufacturing, Volume 29Author(s): Dongdong Gu, Xiangwei Rao, Donghua Dai, Chenglong Ma, Lixia Xi, Kaijie Lin In this study, a laser-based additive manufacturing route of selective laser melting (SLM) was applied to fabricate carbon nanotubes (CNTs) reinforced Al-based nanocomposites with tailored microstructures and excellent mechanical properties. The densification behavior, microstructure features and mechanical properties were investigated and the relationship between process and property was established. The results showed that the applied laser power and scan speed were the governing factors of the densification behavior of SLM-processed Al-based nanocomposites. SLM processing of 0.5 wt.% CNTs/AlSi10Mg nanocomposite powder led to the formation of three typical microstructures including the primary Al9Si cellular dendrites decorated with fibrous Si, the in situ Al4C3 covered on CNTs, and the precipitated Si inside the cellular grains. As the optimal SLM processing parameters of laser power of 350 W and scan speed of 2.0 m/s were applied, the fully dense SLM-processed CNTs/Al-based nanocomposites exhibited high microhardness of 154.12 HV0.2, tensile strength of 420.8 MPa and elongation of 8.87%, due to the formation of high densification and ultrafine microstructure. The grain refinement effect, Orowan looping system and load transfer are considered as three strengthening mechanisms occurred simultaneously during tensile tests, leading to excellent mechanical properties of SLM-processed CNTs/Al-based nanocomposites.
  • Multi-scale computational modeling of residual stress in selective laser
           melting with uncertainty quantification
    • Abstract: Publication date: October 2019Source: Additive Manufacturing, Volume 29Author(s): Daniel Moser, Michael Cullinan, Jayathi Murthy Selective laser melting (SLM) is a powder-based additive manufacturing technique which creates parts by fusing together successive layers of powder with a laser. The quality of produced parts is highly dependent on the proper selection of processing parameters, requiring significant testing and experimentation to determine parameters for a given machine and material. Computational modeling could potentially be used to shorten this process by identifying parameters through simulation. However, simulating complete SLM builds is challenging due to the difference in scale between the size of the particles and laser used in the build and the size of the part produced. Often, continuum models are employed which approximate the powder as a continuous medium to avoid the need to model powder particles individually. While computationally expedient, continuum models require as inputs effective material properties for the powder which are often difficult to obtain experimentally. Building on previous works which have developed methods for estimating these effective properties along with their uncertainties through the use of detailed models, this work presents a part scale continuum model capable of predicting residual thermal stresses in an SLM build with uncertainty estimates. Model predictions are compared to experimental measurements from the literature.
  • Application of thermotropic liquid crystalline polymer reinforced
           acrylonitrile butadiene styrene in fused filament fabrication
    • Abstract: Publication date: October 2019Source: Additive Manufacturing, Volume 29Author(s): Mubashir Q. Ansari, Alec Redmann, Tim A. Osswald, Michael J. Bortner, Donald G. Baird In this work, acrylonitrile butadiene styrene (ABS) was reinforced with a thermotropic liquid crystalline polymer (TLCP) for use in Fused Filament Fabrication (FFF). As ABS and the selected TLCP do not exhibit overlapping processing temperatures, the composite filaments were generated using a dual extrusion technology which allows processing of such matrix-TLCP combinations. The 40.0 wt.% TLCP/ABS filaments exhibited a tensile strength and modulus of 169.2 ± 4.0 MPa and 39.9 ± 3.7 GPa, respectively, due to a nearly continuous reinforcement of the filament. The postprocessing of the filaments in FFF was carried out below the melting temperature of the TLCP, which allowed the printer to take sharp turns despite having nearly continuous reinforcement. On the contrary, the use of commercially available continuous carbon fiber/nylon 6 was found to avoid printing regions which required sharp turns. On printing with the 40.0 wt.% TLCP/ABS filaments, the tensile strength and modulus in the print direction were 74.9 ± 2.4 MPa and 16.5 ± 0.8 GPa, respectively. The compression molded specimens exhibited a tensile strength and modulus of 79.6 ± 4.4 MPa and 12.3 ± 1.2 GPa, respectively, whereas the injection molded specimens exhibited 51.3 ± 3.0 MPa and 4.5 ± 0.1 GPa, respectively.
  • Direct fabrication of bimetallic Ti6Al4V+Al12Si structures via additive
    • Abstract: Publication date: October 2019Source: Additive Manufacturing, Volume 29Author(s): Yanning Zhang, Amit Bandyopadhyay Ti6Al4V + Al12Si compositionally graded cylindrical structures were fabricated on a Ti6Al4V substrate using laser engineered net shaping (LENS™) process. LENS™ fabricated materials had two regions of Ti6Al4V + Al12Si compositions, a pure Al12Si, and a pure Ti6Al4V area. Microstructural changes were affected by both laser power and compositional variations. In addition, TiSi2 and Ti3Al phase formations were also identified in low and high laser power processed Ti6Al4V + Al12Si sections, respectively. Moreover, the high laser power processed Ti6Al4V + Al12Si section showed the highest hardness value of 685.6 ± 10.6 HV0.1, which was caused due to the formation of new intermetallic phases. This high hardness section exhibited brittle failure modes during compression tests, while the pure Al12Si sections showed ductile deformation. The maximum compressive strengths of Ti6Al4V + Al12Si compositionally graded material was 507.8 ± 52.0 MPa. Our results show that compositionally gradient bulk structures of Ti6Al4V and Al12Si can be directly manufactured using additive manufacturing, however, performances can vary significantly based on process parameters and compositional variations.Graphical abstractGraphical abstract for this article
  • Influence of scan pattern and geometry on the microstructure and
           soft-magnetic performance of additively manufactured Fe-Si
    • Abstract: Publication date: October 2019Source: Additive Manufacturing, Volume 29Author(s): A. Plotkowski, J. Pries, F. List, P. Nandwana, B. Stump, K. Carver, R.R. Dehoff The influence of geometry and scan pattern on the microstructure evolution and magnetic performance of additively manufactured Fe-3Si components was investigated. To reduce eddy current losses, novel geometries were designed and built and the microstructure and properties of these samples were characterized. The laser scan pattern was shown to strongly influence both the as-built grain structure and strength of the crystallographic texture, resulting in measurable changes in the as-built magnetic performance. In thin wall samples, heat treatment resulted in an increase in the maximum relative magnetic permeability and decrease in power losses in most samples, consistent with grain growth. However, decreases in the spacing between thin walls to increase the stacking factor of the cross-section was shown to result in unwanted electrical shorting between walls and an increase in eddy current losses. Compared to simple parallel plate construction and a mesh structure, a novel cross-section design based on the Hilbert space filling curve was found to produce the lowest power losses. The mechanisms behind these results were explored using a combination of heat conduction and electromagnetic simulations, providing a route for future component and process optimization.
  • The m4 3D Printer: A multi-material multi-method additive manufacturing
           platform for future 3D printed structures
    • Abstract: Publication date: Available online 2 August 2019Source: Additive ManufacturingAuthor(s): Devin J. Roach, Craig M. Hamel, Conner K. Dunn, Marshall V. Johnson, Xiao Kuang, H. Jerry Qi The advent of additive manufacturing (AM), also often referred as 3D printing, has enabled the rapid production of parts with complex geometries that are either labor-intensive or unrealizable by traditional manufacturing methods. Many existing 3D printing technologies, however, only allow one material to be printed at one time, while many applications require the integration of different materials, which sometimes cannot be printed by one AM technology. In this paper, a novel multi-material multi-method (m4) 3D printer comprised of multiple AM technologies is presented as a solution to the current limitations. This printer fosters the advancement of AM by combining materials traditionally unable to be printed concurrently while adding functionality to printed parts. The m4 3D printer integrates four AM technologies and two complementary technologies onto one single platform, including inkjet (IJ), fused filament fabrication (FFF), direct ink writing (DIW), and aerosol jetting (AJ), along with robotic arms for pick-and-place (PnP) and photonic curing for intense pulsed light (IPL) sintering. The integration of these AM technologies and PnP into a single platform allows for rapid fabrication of complex devices, providing a wide range of functionalities with applications ranging from soft robotics and flexible electronics to medical devices.
  • Intrinsic strain aging, Σ3 boundaries, and origins of cellular
           substructure in additively manufactured 316L
    • Abstract: Publication date: October 2019Source: Additive Manufacturing, Volume 29Author(s): Andrew J. Birnbaum, John C. Steuben, Erin J. Barrick, Athanasios P. Iliopoulos, John G. Michopoulos The observation of sub-grained cellular features in additively manufactured (AM)/selectively laser melted (SLM) 316L stainless steel components has remained an interesting, though incompletely understood phenomenon. However, the recently observed correlation linking the presence of these features with significantly enhanced mechanical strength in SLM 316L materials has driven a renewed interest and effort toward elucidating the mechanism(s) by which they are formed. To date, the dominant hypothesis, cellular solidification followed by dislocation-solute entanglement, remains incompatible with the ensemble of reported observations from multiple independent studies. This effort offers direct evidence of a previously unrecognized interaction of phenomena, that, when acting in concert, give rise to this commonly observed substructure. These phenomena include SLM-induced intrinsic strain-aging, Cottrell atmosphere formation, and twin-boundary enhanced mass diffusion to structural defects. Furthermore, evidence is provided to support the proposed theory that the observed chemical heterogeneity coincident with dislocation cell structures is actually the result of local, strain energy density induced solid state diffusion.Graphical abstractGraphical abstract for this article
  • Additive manufacturing of thin alumina ceramic cores using binder-jetting
    • Abstract: Publication date: October 2019Source: Additive Manufacturing, Volume 29Author(s): Shuangjun Huang, Chunsheng Ye, Huoping Zhao, Zitian Fan Binder-jetting, an additive manufacturing process and relatively low-cost technology is utilized to deposit complex-shaped thin ceramic cores. In this study, for enhancing sintering quality, a decomposable binder was prepared using binder-jetting by dispersing different contents of zirconium basic carbonate (ZBC) into an inorganic colloidal binder. The effects of different ZBC contents on the printability of the binder and the performance characteristics of the ceramic cores by binder-jetting were investigated. The results show that the surface tension of the binder decreases with the increasing of ZBC contents, indicating that the addition of ZBC particles perturbs the interaction between water molecules. The presence of newly generated ZrO2 particles decomposed by ZBC demonstrated a significant effect on the mechanical properties of the ceramic cores. The sintered density increased by about 44%, the bending strength improved from 60 to 79 MPa, and linear shrinkage decreased from 20 to 13% after sintering at 1500 °C as the ZBC content was increased from 0 to 35 wt%.
  • Factors that affect the properties of additively-manufactured AlSi10Mg:
           porosity versus microstructure
    • Abstract: Publication date: Available online 25 July 2019Source: Additive ManufacturingAuthor(s): Wen Hao Kan, Yves Nadot, Matthew Foley, Lionel Ridosz, Gwénaëlle Proust, Julie M. Cairney Depending on the available laser powder bed fusion (LPBF) system, and the intended application, the use of highly-optimized LPBF parameters to fabricate near-perfect density alloys may not be feasible, economical or required. Thus, it is important to understand how sub-optimal density and microstructure can simultaneously affect the mechanical properties of alloys. Here we study the microstructure and properties of an AlSi10Mg alloy fabricated with sub-optimal parameters and investigate the effectiveness of post-processing by hot isostatic pressing (HIP) and T6 heat treatment. Defects were characterized using micro-computed tomography while the microstructure was analysed using transmission and scanning electron microscopy. The as-built microstructure features dendritically-arranged nano-crystalline Si particles that are favourable for high hardness, strength and impact toughness while T6 generally caused these properties to degrade. HIP was unable to close large defects due to trapped gases, which limited fatigue life improvements. Defects oriented normal to the loading axis (or parallel to the fracture plane) are very detrimental, but when oriented favourably, the alloy was still able to achieve comparable strength and ductility to results reported in literature for LPBF-fabricated AlSi10Mg alloys. Interestingly, the anisotropic nano-crystalline Si structures of the as-built alloy resulted in substantially improved toughness even when defects were oriented unfavourably.Graphical abstractGraphical abstract for this article
  • Manufacturing of gypsum-sisal fiber composites using Binder Jetting
    • Abstract: Publication date: Available online 21 July 2019Source: Additive ManufacturingAuthor(s): Arthur Wilson Fonseca Coelho, Rossana Mara da Silva Moreira Thiré, Anna Carla Araujo Among additive manufacturing (AM) technologies, binder jetting (BJ) produces workpieces that could be used in a great variety of applications, such as decorative parts, prototypes, foundry molds, bone implants, and others. This technique includes the powder deposition to form the layers, binder application, and post-processing to enhance mechanical properties. Fibers can be mixed with traditional raw material powder in order to produce composite parts that are stronger. Sisal fibers are considered to be a promising reinforcement in composites because of their low cost, high strength, and lack of risk to human health. In Brazil, sisal fibers are abundant and there has been no previous study on the application of this fiber in binder jetting. This article proposes the production of gypsum-sisal fiber parts using BJ and the analysis of the effects of some manufacturing parameters, such as the presence of fiber, printing orientation, and post-processing. A material characterization is performed on raw materials and printed parts in the form of thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). A complete 24 factorial design for analysis of variance was performed to evaluate the mechanical strength and porosity of the manufactured parts. It was observed that the fibers had a positive influence on the mechanical strength of the infiltrated parts, but a loss of strength was verified on the green parts. The reason for a loss of mechanical strength correlated with the increase in porosity caused by the fiber during the printing process; however, this increased porosity contributed to a more efficient infiltration post-processing.
  • 3D-printed phononic crystal lens for elastic wave focusing and energy
    • Abstract: Publication date: October 2019Source: Additive Manufacturing, Volume 29Author(s): S. Tol, F.L. Degertekin, A. Erturk We explore elastic wave focusing and enhanced energy harvesting by means of a 3D-printed Gradient-Index Phononic Crystal Lens (GRIN-PCL) bonded on a metallic host structure. The lens layer is fabricated by 3D printing a rectangular array of cylindrical nylon stubs with varying heights. The stub heights are designed to obtain a hyperbolic secant distribution of the refractive index to achieve the required phase velocity variation in space, hence the gradient-index lens behavior. Finite element simulations are performed on composite unit cells with various stub heights to obtain the lowest antisymmetric mode Lamb wave band diagrams, yielding a correlation between the stub height and refractive index. The elastic wave focusing performance of lenses with different design parameters (gradient coefficient and aperture size) is simulated numerically under plane wave excitation. It is observed that the focal points of the wider aperture lens designs have better consistency with the analytical beam trajectory results. Experiments are conducted using a PA2200 nylon lens bonded to an aluminum plate to demonstrate wave focusing and enhanced energy harvesting within the 3D-printed GRIN-PCL domain. The piezoelectric energy harvester at the focal region of the GRIN-PCL produces 3 times more power output than the baseline harvester at the same distance in the flat plate region. The results show that 3D printing can provide a simple and practical method for implementing phononic crystal concepts with minimal modification of the host structure.
  • Additive manufacturing of maraging steel-H13 bimetals using laser powder
           bed fusion technique
    • Abstract: Publication date: Available online 20 July 2019Source: Additive ManufacturingAuthor(s): Sajad Shakerin, Amir Hadadzadeh, Babak Shalchi Amirkhiz, Seyedamirreza Shamsdini, Jian Li, Mohsen Mohammadi In this paper, maraging steel powder was deposited on top of an H13 tool steel using laser powder bed fusion (LPBF) technique. The mechanical properties, microstructure, and interfacial characteristics of the additively manufactured MS1-H13 bimetals were investigated using different mechanical and microstructural techniques. Several uniaxial tensile tests and micro-hardness indentations were performed to identify the mechanical properties of the additively manufactured bimetal. Advanced electron microscopy techniques including electron backscatter diffraction and transmission electron microscopy were used to identify the mechanism of interface formation. In addition, the microstructure of the additively manufactured maraging steel along with the conventionally fabricated substrate-H13 were studied. It was concluded that, a very narrow interface was formed between the additively manufactured maraging steel and the conventional H13 without forming cracks or discontinuities. The first deposited layers possessed the highest hardness due to grain size refinement, solid solution strengthening, and cellular solidification structure. Finally, under uniaxial tensile loading, the additively manufactured bimetal steel failed from the underlying tool steel, indicating a robust interface.
  • Accelerated refilling speed in rapid stereolithography based on
           nano-textured functional release film
    • Abstract: Publication date: October 2019Source: Additive Manufacturing, Volume 29Author(s): Li Wang, Yu Luo, Zhiqiang Yang, Wanjing Dai, Xiaoyang Liu, Jingyuan Yang, Bingheng Lu, Lijia Chen Nowadays, along with the demand for new technologies and new materials, a revolution in 3D printing technology is emerging. In recent years, stereolithography 3D printing has been widely used in both academia and industry, due to its fast forming speed, high precision, and low-cost advantages. The continuous liquid interface production technology has made the printing speed even faster. However, the process of resin refilling constrains the printing speed and the printing capabilities of such technologies, since only hollow structures can be fabricated. In this study, a nano-textured hydrophobic PDMS contacting layer and an oxygen-permeable membrane were bonded together as the functional release film. The oxygen inhibition layer was successfully maintained by the molecular oxygen permeated through the composite release film, achieving rapid stereolithography, and key factors that affecting resin refilling are selectively studied by the orthogonal experiment. Crucially, according to the simulation and experimental results, the adoption of the hydrophobic nano-texture not only increased the refilling speed of the resin by two times and reduced the printing time by nearly 25%, but also improved the printing reliability by reducing the vacuum (negative pressure) caused by the original slow refilling speed. Additionally, optical simulations also demonstrated that the nano-texture would not influence the curing effect of the resin. This work proposed a promising strategy for rapid stereolithography of 3D models containing larger cross-sectional areas.Graphical abstractA nano-textured PDMS contacting layer and an oxygen-permeable membrane were bonded together as the printing substrate, providing high oxygen permeability to form an oxygen inhibition layer. The introduction of the nano-texture on PDMS not only increased the refilling speed of the resin by two times and reduced the printing time by nearly 25%, and the printing reliability of larger cross-sectional areas was remarkably improved.Graphical abstract for this article
  • Compressive creep of AlSi10Mg parts produced by selective laser melting
           additive manufacturing technology
    • Abstract: Publication date: Available online 17 July 2019Source: Additive ManufacturingAuthor(s): Naor Elad Uzan, Barak Ratzker, Peri Landau, Sergey Kalabukhov, Nachum Frage Compressive creep properties of AlSi10Mg parts produced by additive manufacturing selective laser melting (AM-SLM) were studied using a spark plasma sintering (SPS) apparatus capable of performing uniaxial compressive creep tests. Stress relief-treated specimens were tested under an applied stress of 100-130 MPa in the 175–225 °C temperature range. Utilizing two different configurations, the creep tests were conducted either with or without a low-density electric current (˜2.63–3.26 A/mm2) flowing through the test specimens. The results revealed that the creep rate increased under the influence of an applied electric current. The creep parameters (i.e., stress exponent n and apparent activation energy Q), were empirically determined. The stress exponent values were found to be 19.6 ± 1.2 and 16.2 ± 1.4 with and without current, respectively, while apparent activation energy was found to be 142 ± 9 kJ/mol and 150 ± 13 kJ/mol with and without current, respectively. The experimental results, together with microstructural examination of specimens, indicate that plastic deformation was controlled by dislocation activity. Furthermore, it is suggested that the annihilation process of dislocations during creep was enhanced by the electric current.
  • Effect of microstructure on the Charpy impact properties of directed
           energy deposition 300M steel
    • Abstract: Publication date: Available online 17 July 2019Source: Additive ManufacturingAuthor(s): Fenggang Liu, Xin Lin, Jing Shi, Yongjian Zhang, Peiying Bian, Xun Li, Yunlong Hu Direct manufacturing techniques, such as directed energy deposition (DED), are able to produce complex components efficiently. In this study, microstructure evolution and impact toughness of DED 300 M ultra-high strength steel are investigated. The results show that the microstructure of the as-deposited DED 300 M ultra-high strength steel is mainly composed of martensite and some blocky bainite. The micro-segregation of elements is observed within the interdendritic area. After heat treatment, the microstructure becomes uniform and consists of martensite and lower bainite. The impact toughness of the as-deposited DED 300 M ultra-high strength steel is 9 J/cm2, while it is significantly increased to 25 J/cm2 after heat treatment. Furthermore, it is observed that the fracture mode of the as-deposited sample is quasi-cleavage fracture. During the process of propagation, the main cracks would go across the martensite packet and deflect in the another one, and secondary cracks also deflected in the high-angle grain boundaries. By contrast, the fracture mode of heat-treated DED 300 M steel is ductile fracture.
  • An analytical method to predict and compensate for residual stress-induced
           deformation in overhanging regions of internal channels fabricated using
           powder bed fusion
    • Abstract: Publication date: Available online 17 July 2019Source: Additive ManufacturingAuthor(s): Amar M. Kamat, Yutao Pei Powder bed fusion (PBF) is ideally suited to build complex and near-net-shaped metallic structures such as conformal cooling channel networks in injection molds. However, warpage occurring due to the residual stresses inherent to this process can lead to shape deviation in the internal channels and needs to be minimized. In this research, a novel analytical model based on the Euler-Bernoulli beam bending theory was developed to estimate the residual stress-induced deformation of internal channels printed horizontally using PBF. The model was used to predict the shape deviation for three different shapes of channel cross sections (circular, elliptical, and diamond-shaped), and showed very good agreement with the experimentally determined shapes of nine different internal channels (three cases per cross-sectional shape). Further, the model predictions were used to compensate for the shape deviation in the design stage, resulting in a reduction in root mean square (RMS) deviation of the circular channel by a factor of 2. The proposed approach is thus expected to be a useful tool to generate design-for-AM guidelines for the additive manufacturing of overhangs and internal channels.
  • High-Throughput Characterization of Fluid Properties to Predict Droplet
           Ejection for Three-Dimensional Inkjet Printing Formulations
    • Abstract: Publication date: Available online 12 July 2019Source: Additive ManufacturingAuthor(s): Zuoxin Zhou, Laura Ruiz Cantu, Xuesheng Chen, Morgan R. Alexander, Clive J. Roberts, Richard Hague, Christopher Tuck, Derek Irvine, Ricky Wildman Inkjet printing has been used as an Additive Manufacturing (AM) method to fabricate three-dimensional (3D) structures. However, a lack of materials suitable for inkjet printing poses one of the key challenges that impedes industry from fully adopting this technology. Consequently, many industry sectors are required to spend significant time and resources on formulating new materials for an AM process, instead of focusing on product development. To achieve the spatially controlled deposition of a printed voxel in a predictable and repeatable fashion, a combination of the physical properties of the ‘ink’ material, print head design, and processing parameters is associated. This study demonstrates the expedited formulation of new inks through the adoption of a high-throughput screening (HTS) approach. Use of a liquid handler containing multi-pipette heads, to rapidly prepare inkjet formulations in a micro-array format, and subsequently measure the viscosity and surface tension for each in a high-throughput manner is reported. This automatic approach is estimated to be 15 times more rapid than conventional methods. The throughput is 96 formulations per 13.1 working hours, including sample preparation and subsequent printability determination. The HTS technique was validated by comparison with conventional viscosity and surface tension measurements, as well as the observation of droplet ejection during inkjet printing processes. Using this approach, a library of 96 acrylate/methacrylate materials was screened to identify the printability of each formulation at different processing temperatures. The methodology and the material database established using this HTS technique will allow academic and industrial users to rapidly select the most ideal formulation to deliver printability and a predicted processing window for a chosen application.
  • Towards additive manufacturing of magnesium alloys through integration of
           binderless 3D printing and rapid microwave sintering
    • Abstract: Publication date: Available online 11 July 2019Source: Additive ManufacturingAuthor(s): Mojtaba Salehi, Saeed Maleksaeedi, Mui Ling Sharon Nai, Manoj Gupta 3D printing (3DP) is a two-step additive manufacturing technique (AM) in which additively manufactured green parts in the first step are transformed into functional parts during the second step. 3DP could attract more interest if a new window of opportunity for its first and second steps is opened. Here we use capillary-mediated binderless 3DP as a novel method to additively manufacture green parts of Mg-5.06Zn-0.15 Zr powder. A unified perspective on the development steps of process parameters to obtain sufficient handling strength and a high level of dimensional accuracy in the green parts without compromising its chemical composition is established by using a scanning electron microscope, X-ray micro-tomography, vibrational spectroscopy, and chemical analysis. For the first time, microwave (MW) sintering is successfully used for densification of the green parts with centimeter-scale dimensions in which the primary chemical composition of the Mg-Zn-Zr powder is retrieved from the green parts, resulting in a compositionally zero-sum AM process. It is found that swelling leads to loss of shape fidelity during MW sintering of the green parts at temperatures ≥ 510 °C. As discussed in the context of thermal and non-thermal effects, MW significantly reduced sintering time by a factor of three to four times when compared to sintering in a conventional furnace. The results of this study suggest the notion of capillary-mediated binderless 3DP as well as MW sintering as a potential alternative for the first and second steps of 3DP, respectively.Graphical abstractGraphical abstract for this article
  • Feasibility Study of Silicone Stereolithography with an Optically Created
           Dead Zone
    • Abstract: Publication date: Available online 9 July 2019Source: Additive ManufacturingAuthor(s): Dong Sung (Danny) Kim, Jakkrit Suriboot, Melissa A. Grunlan, Bruce L. Tai Vat photopolymerization (VP) of silicone can produce better finish and higher resolution than the conventional extrusion-based method. One challenge in the current bottom-up VP processes is the separation that forms between the cured part and vat at each layer. Oxygen-inhibition is commonly adopted as a solution (i.e. “dead zone”), but it is limited by the size, material, and environment. Herein, a method to optically create the dead zone by low one photon polymerization (LOPP) is investigated. LOPP is achieved by a low-absorbance wavelength and a gradient light beam. In this study, two sets of the experiments, stationary exposure and moving exposure, were conducted with two low-absorbance wavelengths (375 nm and 385 nm) for a formulated UV-curable silicone. The first experiment measured the effect of beam power; the second experiment measured the effect of scanning speed. The results show that the lower-absorbance wavelength (385 nm) generates a larger, more stable dead zone and a smaller curing spot in both experiments, while the 375 nm wavelength produces a rapidly changed dead zone in the stationary condition and nearly no dead zone in the moving condition. The curing speed of 385 nm at the same power level was 10 times slower than 375 nm, but could be scaled up non-linearly by the beam power. A tripled light power of 385 nm can accelerate the process by a factor of 7 and be comparable to that of 375 nm. Thus, this study confirms the feasibility of an optically created dead zone and also uncovers the necessity of high-power light source for this application.
  • Flow analysis of the polymer spreading during extrusion additive
    • Abstract: Publication date: Available online 9 July 2019Source: Additive ManufacturingAuthor(s): Jean-François Agassant, Franck Pigeonneau, Lucas Sardo, Michel Vincent The spreading of molten polymer between the moving printing head and the substrate in extrusion additive manufacturing is studied. Finite element computation and an analytical model have been used. The hypotheses of the analytical model are qualitatively justified by the results of the numerical computation. The analytical calculation is a powerful tool to rapidly evaluate the relationships between processing parameters (extrusion rate, printing head velocity, gap between the printing head and the substrate) and some characteristics of the deposition (dimensions of the deposited filament, pressure at the printing head nozzle, separating force between substrate and printing head). An isothermal hypothesis is discussed. The viscous non-Newtonian behavior is accounted for through an approximate shear thinning power law model. A printing processing window is defined following several requirements: a continuous deposit, without spreading in front of the printing head, maximum and minimum spreading pressures, an upper-limit for the separating force between head and substrate.
  • Novel microstructural features of selective laser melted lattice struts
           fabricated with single point exposure scanning
    • Abstract: Publication date: Available online 8 July 2019Source: Additive ManufacturingAuthor(s): E. Onal, A.E. Medvedev, M.A. Leeflang, A. Molotnikov, A.A. ZadpoorGraphical abstractGraphical abstract for this article Single point exposure scanning strategy is a largely unexplored selective laser melting (SLM) technique to fabricate lattice structures without an STL file. In this work, we used a series of>50 sets of processing parameters to systematically study the SLM fabrication of vertical struts made of Ti-6Al-4 V. In addition, the effects of (partial) re-melting and latent heat on hardness and developed microstructure were investigated. We demonstrate that the strut dimensions could be controlled by the processing parameters with higher energy inputs, resulting in larger strut diameters up to a saturation point (i.e. 520 µm corresponding to 0.5 J energy). The single point exposure method yielded keyhole shaped pores that were up to 4 times smaller than those observed, typically when the hatching and contour technique is used. Transmission electron microscopy (TEM) images revealed ultrafine (˜200-300 nm) and homogeneous microstructure in the double-melted specimens as compared to the classic microstructure of SLM Ti6Al4V observed in the single melted strut: hierarchical α'-laths with varying sizes (0.1-1 μm). Finally, we investigated the texture and identified the retained β phase, which enabled us to check the Burgers orientation relationship (BOR) between α' and β phases. This is the first attempt to systematically study the microstructural features resulting from the single point exposure SLM technique for lattice structures made from Ti6Al4V, and exhibits the processability window that could be used to engineer the microstructure of such structures.
  • Neutron diffraction residual stress determinations in Fe3Al based iron
           aluminide components fabricated using wire-arc additive manufacturing
    • Abstract: Publication date: Available online 2 July 2019Source: Additive ManufacturingAuthor(s): Chen Shen, Mark Reid, Klaus-Dieter Liss, Zengxi Pan, Yan Ma, Dominic Cuiuri, Stephen van Duin, Huijun Li The Wire-Arc Additive Manufacturing (WAAM) process is an increasingly attractive method for producing porosity-free metal components. However, the residual stresses and distortions resulting from the WAAM process are major concerns as they not only influence the part tolerance but can also cause premature failure in the final component during service. The current paper presents a method for using neutron diffraction to measure residual stresses in Fe3Al intermetallic wall components that have been in-situ additively fabricated using the WAAM process with different post-production treatments. By using averaging methods during the experimental setup and data processing, more reliable residual stress results are obtained from the acquired neutron diffraction data. In addition, the present study indicates that the normal residual stresses are significant compared to normal butt/fillet welding samples, which is caused by the large temperature gradient in this direction during the additive layer depositions.
  • Development of a Hot-Melt Extrusion (HME) process to produce drug loaded
           Affinisol™ 15LV filaments for Fused Filament Fabrication (FFF) 3D
    • Abstract: Publication date: Available online 2 July 2019Source: Additive ManufacturingAuthor(s): Elke Prasad, Muhammad T. Islam, Daniel J. Goodwin, Andrew J. Megarry, Gavin W. Halbert, Alastair J. Florence, John Robertson The aim of the present work was to develop a pilot scale process to produce drug-loaded filaments for 3D printing of oral solid dose forms by fused filament fabrication (FFF). Using hot melt extrusion, a viable operating space and understanding of processing limits were established using a hydrophilic polymer (hydroxypropyl methylcellulose (HPMC) - Affinisol™ LV15). This was then extended to formulate paracetamol (PCM) loaded Affinisol™ 15LV filaments across a wide range of compositions (5 - 50 wt% drug). From the process development work, challenges in achieving a pilot scale process for filament production for pharmaceutical applications have been highlighted. 3D printing trials across the range of compositions demonstrated limitations concerning the ability to print successfully across all compositions. Results from characterisation techniques including thermal and mechanical testing when applied to the formulated filaments indicated that these techniques are a useful predictive measure for assessing the ability to print a given formulation via filament methods. Oral solid dosage forms of variable surface area to mass ratios printed from suitable filament compositions demonstrated the ability to modify the release rates of drug for fixed formulations across substantial timescales.
  • Integrated manufacture of polymer and conductive tracks for real-world
    • Abstract: Publication date: Available online 2 July 2019Source: Additive ManufacturingAuthor(s): Barbara Urasinska-Wojcik, Neil Chilton, Peter Todd, Christopher Elsworthy, Myles Bates, Gethin Roberts, Gregory J. Gibbons The present study demonstrates for the first time a unique UK-designed and built Additive Manufacturing (AM) hybrid system that combines polymer based structural deposition with digital deposition of electrically conductive elements. This innovative manufacturing system is based on a multi-planar build approach to improve on many of the limitations associated with AM, such as poor surface finish, low geometric tolerance and poor robustness. Specifically, the approach involves a multi-planar Material Extrusion (ME) process in which separated build stations with up to 5 axes of motion replace traditional horizontally-sliced layer modelling. The construction of multi-material architectures also involved using multiple print systems in order to combine both ME and digital deposition of conductive material. To demonstrate multi-material 3D Printing (3DP) we used three thermoplastics to print specimens, on top of which a unique Ag nano-particulate ink was printed using a non-contact jetting process, during which drop characteristics such as shape, velocity, and volume were assessed using a bespoke drop watching system. Electrical analysis of printed conductive tracks on polymer surfaces was performed during mechanical testing (static tensile and flexural testing and dynamic fatigue testing) to assess robustness of the printed circuits. Both serpentine and straight line patterns were used in the testing of Ag particle loaded ink and they showed very similar resistance changes during mechanical exposure. Monitored resistance and stress changed as a function of strain exhibiting hysteresis with more prominent residual strain during stretching and compression cycles and 3-point bending flexural tests of PA and CoPA substrates. Bare and encapsulated tracks exhibited low electrical resistivity (1-3*10-6Ω*m), and its change was more rapid on ABS and minor on PA and CoPA when increasing tensile and flexural strain up to 1.2% and 0.8%, respectively. Resistance of Ag tracks on ABS also increased rapidly during fatigue testing and the tracks easily fractured during repeated stretching-compression cycles at 1% and 1.2% strain. No resistance changes of Ag tracks printed on PA and CoPA were observed at lower strain amplitudes whereas at higher strain amplitudes these changes were the lowest for conductive tracks on CoPA. Thermal analyses were conducted to determine the printed material’s glass transition temperature (Tg), stability and degradation behavior to find the optimum annealing conditions post printing. The novel AM printer has the ability to fabricate fully functional objects in one build, including integrated printed circuitry and embedded electronics. It enables product designers and manufactures to produce functional saleable electronic products. This new technology also gives the opportunity for designers to improve existing products, as well as create new products with the added advantages of geometrically unconstrained 3DP.
  • The effect of texture on the anisotropy of thermophysical properties of
           additively manufactured AlSi10Mg
    • Abstract: Publication date: Available online 29 June 2019Source: Additive ManufacturingAuthor(s): Einat Strumza, Ori Yeheskel, Shmuel Hayun The process of additive manufacturing (AM) has rapidly developed over the past two decades and is now addressing the needs of industry for fast production of samples with tailored properties and complex geometries. One of the most common alloys fabricated from powder using the Laser Powder Bed Fusion (L-PBF) method is AlSi10Mg. The effects of the inherent anisotropy and existing porosity in AM AlSi10Mg were investigated in terms of thermophysical properties, namely thermal conductivity, diffusivity, heat capacity and thermal expansion. These properties were measured in the two principal directions, namely parallel and perpendicular to the printing direction (i.e., in the Z- and X-directions, respectively). In both cases, the sample showed abnormal thermal expansion and conductivity, as compared to a conventionally fabricated sample. After heat treatment, macro- and microstructure analysis confirmed that thermally induced porosity (TIP) had occurred. The anisotropic behaviors of thermal conductivity, diffusivity and thermal expansion were found to be related to the texture, preferred orientation and pore distribution of the aluminum grains in the L-PBF-treated samples.
  • The Formation and Kr-ion Irradiation Behaviour of New Microstructural
           Features in Additively Manufactured Titanium Aluminium Alloy
    • Abstract: Publication date: Available online 29 June 2019Source: Additive ManufacturingAuthor(s): Hanliang Zhu, Yan Ma, Tao Wei, Huijun Li, Robert Aughterson, Gregory LumpkinABSTRACTNew microstructural features were found in the TiAl alloy manufactured using the gas tungsten arc welding-based additive manufacturing technology. The ion-irradiation response of the new microstructure features were investigated in-situ via irradiation with 1 MeV Kr2+ ions at room and 873 K. Examination of the microstructure showed that the typical lamellar microstructure consisting of α2-Ti3Al and γ-TiAl phases formed α2/γ lamellar interfaces and γ/γ twin boundaries. Apart from this, the γ lamellae were also found to form γ/γ lamellar boundaries with the two γ lamellae in the same orientation or the  // orientation relationship. This is not observed in the TiAl alloys fabricated using traditional alloy fabrication methods. Kr ion-irradiation at room and elevated temperatures resulted in no significant difference in the morphologies of most radiation-induced defects in the orientated γ lamellae and the orientated γ lamellae. However, the areas of the new boundaries exhibited different damage morphologies in comparison with the traditional γ/γ twin boundaries. The formation mechanisms of the new microstructural features formed in the additive manufacturing process and their irradiation behaviour are investigated and discussed.Graphical Graphical abstract for this article
  • The Effects of Material Anisotropy on Secondary Processing of Additively
           Manufactured CoCrMo
    • Abstract: Publication date: Available online 28 June 2019Source: Additive ManufacturingAuthor(s): Patxi Fernandez-Zelaia, Vinh Nguyen, Hayley Zhang, Arkadeep Kumar, Shreyes N. Melkote Components produced by near net shape additive manufacturing processes often require subsequent subtractive finishing operations to satisfy requisite surface finish and geometric tolerances. It is well established that the microstructure and properties of the as-built component are sensitive to the additive processing history. Therefore, downstream secondary processes may be affected by the as-built components’ mechanical behavior. In this work we study the sensitivity of secondary machining operations on CoCrMo samples produced via selective laser melting. Utilizing novel high-throughput mechanical testing, microstructure characterization, and a rigorous statistical analysis we investigate the degree of material anisotropy present in the as-built material. We then study the effects of this anisotropy on secondary processing via slot milling experiments. Our results indicate that mechanical anisotropy is driven by both the morphology of the microstructure as well as crystallographic texture. The machining force response is correspondingly sensitive to these sources of anisotropy, which has the potential to impact how manufacturers finish additively built parts.
  • Experimental Validation of Thermo-mechanical Part-Scale Modeling for Laser
           Powder Bed Fusion Processes
    • Abstract: Publication date: Available online 25 June 2019Source: Additive ManufacturingAuthor(s): Michael Gouge, Erik Denlinger, Jeff Irwin, Chao Li, Pan Michaleris Numerical simulation has been posited as a key tool to reduce the unwanted distortion which occurs during laser powder bed fusion additive manufacturing, yet the scale and speed of the process makes traditional moving source modeling impractical. In this work a part-scale model is validated for the distortion modeling of laser powder bed fusion manufacture. The model uses an automatically generated adaptive voxel mesh which reduces the size of the finite element mesh and thus the computational time required to simulate large and complex additive geometries. The approach address several of the major challenges of effects part-scale modeling, namely the addition of new material into the simulation, the voxel meshing of thin or detailed geometry sections, and the efficient meshing of thick cross sections. The part-scale simulation uses input from a detailed small-scale analysis as part of a multi-scale approach. However, the part-scale approach could also be applied as part of a traditional experimentally calibrated inherent strain modeling approach. Validation is achieved by comparing the three-dimensional scans of three manufactured parts, a small thin walled Inconel 625 Compliant Cylinder, a small Inconel 718 build with both very thin and very thick sections, and an industrial scale part formed from AlSi10Mg. The models show a maximum peak distortion error of 13% and a minimum Correlation of 90.5% for comparisons made at selected points. A comparison of build versus simulation time shows that the adaptive meshing allows the model to run in much less time than it takes for the parts to be constructed. A presentation of thermal and mechanical results demonstrates the part-scale model's ability to capture the complex evolution of the thermo-mechanical behavior of components formed using powder bed fusion.
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
Tel: +00 44 (0)131 4513762
Fax: +00 44 (0)131 4513327
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