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Publisher: Springer-Verlag (Total: 2352 journals)

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 Acta Metallurgica Sinica (English Letters)Journal Prestige (SJR): 0.576 Citation Impact (citeScore): 2Number of Followers: 7      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1006-7191 - ISSN (Online) 2194-1289 Published by Springer-Verlag  [2352 journals]
• Hot Deformation Behavior of an Ultra-High-Strength
Fe–Ni–Co-Based Maraging Steel
• Abstract: Hot processing behavior of an ultra-high-strength Fe–Ni–Co-based maraging steel was studied in temperature range of 900–1200 °C and strain rate range of 0.001–10 s−1. Deformation processing parameters and optimum hot working window were characterized via flow stress analysis, constitutive equation construction, hot processing map calculation and microstructure evolution, respectively. Critical strain value for dynamic recrystallization was determined through theoretical mathematical differential method: the inflection point of θ–σ and − ∂θ/∂σ − σ curves. It was found that the flow stress increased with the decrease in deformation temperature and increase in the strain rate. The power dissipation maps in the strain range of 0.1–0.6 were entirely similar with the tendency of contour lines which implied that strain had no strong effect on the dissipation maps. Nevertheless, the instability maps showed obvious strain sensitivity with increasing strain, which was ascribed to the flow localization and instability. The optimized hot processing window of the experimental steel was obtained as 1100–1200 °C/0.001–1 s−1 and 1000–1100 °C/0.001–0.1 s−1, with the efficiency range of 20–40%. Owing to high Mo content in the experimental steel, high dynamic activation energy, Q = 439.311 kJ mol−1, was achieved, indicating that dynamic recrystallization was difficult to occur in the hot deformation process, which was proved via microstructure analysis under different hot deformation conditions.
PubDate: 2019-09-01

• Fabrication and Characterization of Nanopillar-Like HA Coating on Porous
Ti6Al4V Scaffold by a Combination of Alkali–Acid-Heat and Hydrothermal
Treatments
• Abstract: Porous titanium scaffold with suitable porous architecture exhibits enormous potentials for bone defect repairs. However, insufficient osteointegration and osteoinduction still remain to open as one of the major problems to achieve satisfactory therapeutic effect. To solve this problem, many studies have been carried out to improve the bioactivity of porous titanium scaffold by surface modifications. In this study, porous Ti6Al4V scaffolds were fabricated using additive manufacturing technique. Porous architectures were built up based on a diamond pore structure unit. Alkali–acid-heat (AH) treatment was applied to create a TiO2 layer on the porous Ti6Al4V scaffold (AH-porous Ti6Al4V). Subsequently, a hydrothermal treatment was employed to enable the formation of HA coating with nanopillar-like morphology on the alkali–acid-heat-treated surface (HT/AH-porous Ti6Al4V). The effects of surface modifications on apatite-forming ability, protein adsorption, cell attachment, cell proliferation and osteogenic gene expression were studied using apatite-forming ability test, protein adsorption assay and in vitro cell culture assay. It was found that the HT/AH-porous Ti6Al4V exhibited the highest apatite formation ability and best affinity to fibronectin and vitronectin. In vitro studies indicated that the mesenchymal stem cells (MSCs) cultured on the HT/AH-porous Ti6Al4V presented improved adhesion and differentiation compared with the porous Ti6Al4V and AH-porous Ti6Al4V.
PubDate: 2019-09-01

• Elastic Properties and Stacking Fault Energies of Borides, Carbides and
Nitrides from First-Principles Calculations
• Abstract: Owing to the excellent elastic properties and chemical stability, binary metal or light element borides, carbides and nitrides have been extensively applied as hard and low-compressible materials. Researchers are searching for harder materials all the time. Recently, the successful fabrication of nano-twinned cubic BN (Tian et al. Nature 493:385–388, 2013) and diamond (Huang et al. Nature 510:250–253, 2014) exhibiting superior properties than their twin-free counterparts allows an efficient way to be harder. From this point of view, the borides, carbides and nitrides may be stronger by introducing twins, whose formation tendency can be measured using stacking fault energies (SFEs). The lower the SFEs, the easier the formation of twins. In the present study, by means of first-principles calculations, we first calculated the fundamental elastic constants of forty-two borides, seventeen carbides and thirty-one nitrides, and their moduli, elastic anisotropy factors and bonding characters were accordingly derived. Then, the SFEs of the {111} < 112 > glide system of twenty-seven compounds with the space group F $$\bar{4}$$ 3m or Fm $$\bar{3}$$ m were calculated. Based on the obtained elastic properties and SFEs, we find that (1) light element compounds usually exhibit superior elastic properties over the metal borides, carbides or nitrides; (2) the 5d transition-metal compounds (ReB2, WB, OsC, RuC, WC, OsN2, TaN and WN) possess comparable bulk modulus (B) with that of cBN (B = 363 GPa); (3) twins may form in ZrB, HfN, PtN, VN and ZrN, since their SFEs are lower or slightly higher than that of diamond (SFE = 277 mJ/m2). Our work can be used as a valuable database to compare these compounds.
PubDate: 2019-09-01

• Hydrogen Storage Performances of Nanocrystalline and Amorphous NdMg 11
Ni +  x wt% Ni ( x  = 100, 200) Alloys Synthesized by Mechanical
Milling
• Abstract: Nanocrystalline and amorphous NdMg12-type NdMg11Ni + x wt% Ni (x = 100, 200) alloys were successfully prepared through ball milling (BM). The microstructures and electrochemical properties were systematically studied to get a more comprehensive understanding of the sample alloys. The maximum discharging capacity could be obtained at only two cycles, indicating that as-milled alloys have superior activation capability. The more the Ni content, the better the electrochemical properties of the as-milled samples. To be specific, the discharge capacities of x = 100 and x = 200 (BM 20 h) samples are 128.2 and 1030.6 mAh/g at 60 mAh/g current density, respectively, revealing that enhancement of Ni content could significantly improve the discharging capacities of the samples. Additionally, milling duration obviously influences the electrochemical properties of the samples. The discharging capacity always rises with milling duration prolonging for the x = 100 sample, but that of the (x = 200) sample shows a trend of first augment and then decrease. The cycling stability of the (x = 100) alloy clearly decreases with extending milling duration, whereas that of the (x = 200) alloy first declines and then augments under the same conditions. In addition, the high rate discharge (HRD) abilities of the sample display the maximal values as milling duration changes. The HRD (HRD = C300/C60 × 100%) values of the as-milled alloys (x = 100, 200) are 80.24% and 85.17%, respectively.
PubDate: 2019-09-01

• Effect of Deposition Potential on Synthesis, Structural, Morphological and
Photoconductivity Response of Cu 2 O Thin Films by Electrodeposition
Technique
• Abstract: The present work describes the effect of deposition potentials on structural, morphological, optical, electrical and photoconductivity responses of cuprous oxide (Cu2O) thin films deposited on fluorine-doped tin oxide glass substrate by employing electrodeposition technique. X-ray diffraction patterns reveal that the deposited films have a cubic structure grown along the preferential (111) growth orientation and crystallinity of the film deposited at − 0.4 V is improved compared to the films deposited at − 0.2, − 0.3 and − 0.5 V. Scanning electron microscopy displays that surface morphology of Cu2O film has a well-defined three-sided pyramid-shaped grains which are uniformly distributed over the surface of the substrates and are significantly changed as a function of deposition potential. Raman and photoluminescence spectra manifest that the film deposited at − 0.4 V has a good crystal quality with higher acceptor concentration compared to other films. UV–visible analysis illustrates that the absorption of Cu2O thin film deposited at − 0.4 V is notably higher compared to other films and the band gap of Cu2O thin films decreases from 2.1 to 2.04 eV with an increase in deposition potential from − 0.2 to − 0.5 V. The frequency–temperature dependence of impedance analysis shows that the film deposited at − 0.4 V has a high conductivity. I–V measurements elucidate that the film deposited at − 0.4 V exhibits a good photoconductivity response compared to films deposited in other deposition potentials.
PubDate: 2019-09-01

• Effects of Isothermal Aging on Microstructure and Mechanical Property of
Low-Carbon RAFM Steel
• Abstract: In order to investigate the microstructure and mechanical property evolution of low-carbon reduced activation ferritic/martensitic (RAFM) steel during isothermal aging, the normalized and tempered specimens were aged at 600 °C for 500, 1000, and 3000 h, respectively. The microstructural evolution with aging time was analyzed, including the precipitation and growth of M23C6 and MX-type carbides as well as the formation of Laves phase. The results indicate that the coarsening of M23C6 is more obvious than that of MX with increase in aging time. During the long-term thermal exposure, the Fe2W Laves phase precipitates adjacent to M23C6 along the prior austenite grain boundaries and packet boundaries. Lower carbon content can delay the precipitation of Laves phase compared to the steel containing higher carbon. In addition, the Laves phase precipitated along boundaries can provide the precipitation strengthening, slightly increasing the tensile strength of low-carbon RAFM steel after aging for 3000 h.
PubDate: 2019-09-01

• Modeling the Dynamic Recrystallization of Mg–11Gd–4Y–2Zn–0.4Zr
Alloy Considering Non-uniform Deformation and LPSO Kinking During Hot
Compression
• Abstract: Hot compression tests of Mg–11Gd–4Y–2Zn–0.4Zr alloy (GWZK114) were conducted at a deformation temperature range of 300–500 °C and a strain rate range of 0.01–10.0 s−1. Based on systematic microstructure observation, it is confirmed that long period stacking ordered (LPSO) phase displays essential and evolving roles on the dynamic recrystallization (DRX) behavior. The results indicate that the plastic deformation is mainly coordinated by simultaneous exist of LPSO kinking of lamella 14H-LPSO phase and DRX at 350–450 °C, and DRX at 500 °C. Further, it is found that the LPSO kinking induced during 350–450 °C can delay the DRX. A phenomenological DRX model of GWZK114 alloy is established to be $$X_{\text{DRX}} = 1 - \exp [ - 0.5(\frac{{\varepsilon - \varepsilon_{\text{c}} }}{{\varepsilon^{*} }})^{0.91} ]$$ . Non-uniform distribution of plastic strain during compression was considered via finite element method and it ensures a good prediction of DRX fraction under a large plastic strain. Meanwhile, an enhanced DRX model, taking its formulation as $$X_{\text{DRX}} = \{ 1 - \exp [ - 0.5(\frac{{\varepsilon - \varepsilon_{c} }}{{\varepsilon^{*} }})^{0.91} ]\} (\frac{T}{226.8} - 1)^{n}$$ , $$n = 3.82\dot{\varepsilon }^{0.083}$$ , is proposed for the first time to capture the hindering effect of 14H-LPSO kinking on DRX behavior. The predicted results of this enhanced DRX model agree well with the experimental cases, where 14H-LPSO kinking is dominated or partially involved (300–450 °C). Besides, a size model of DRX grains is also established and can depict the evolution of DRX grain size for all the investigated compression conditions with accounting for temperature rising at high strain rates (5 s−1 and 10 s−1).
PubDate: 2019-09-01

• Mechanical and Damping Behavior of Age-Hardened and Non-age-hardened Al
Alloys After Friction Stir Processing
• Abstract: This study investigated the microstructure, mechanical, and damping properties of a non-age-hardened Al alloy (5086) and an age-hardened Al alloy (7075) after friction stir processing (FSP). Microstructural analyses indicate that FSP led the grain refinement of samples, and the grains size decreased with the decrease in the tool rotation rate. Furthermore, FSP with low rotation rate promotes the η phase precipitation in the 7075 alloy, causing the micron-sized particles in the 5086 alloy to break up. After being subjected to FSP with low rotation rate, the 5086 and 7075 alloys exhibited excellent mechanical and damping properties. Such improved properties were ascribed to their equilibrium grain boundaries, fine grain, low density of dislocations, high fraction of high misorientation angle, and uniform particle distribution.
PubDate: 2019-09-01

• Corrosion Properties of Calcium Stearate-Based Hydrophobic Coatings on
Anodized Magnesium Alloy
• Abstract: A calcium stearate-based hydrophobic coating was formed on an anodized magnesium alloy by the electrodeposition method. The influences of the working voltages on the characteristics of the coatings were researched. The results indicate that the working voltages have significant effects on the morphology, thickness, roughness, and wettability of the hydrophobic coatings, but little influence on the phase composition. Higher working voltages promote the nucleation of the coatings during the deposition process. The thickness, roughness, and water contact angle of the coatings increase with the increase in working voltage. In addition, the influences of the working voltages on the corrosion properties and corrosion mechanisms of the coated magnesium alloys are discussed in detail. When the working voltage is 50 V, the best corrosion resistance is obtained, but when the working voltages are 20 V and 100 V, respectively, a low corrosion resistance is obtained because of the presence of the thinner and cracked coating on the substrate surfaces.
PubDate: 2019-09-01

• Influence of Island Scanning Strategy on Microstructures and Mechanical
Properties of Direct Laser-Deposited Ti–6Al–4V Structures
• Abstract: To investigate the influence of island scanning on the microstructures and mechanical properties of direct laser-deposited Ti–6Al–4V structures, two samples are prepared using island scanning and orthogonal successive scanning, respectively. The microstructures, relative density, and mechanical properties of the samples prepared using these two scanning strategies are compared. Each sample exhibits columnar β-grain morphology and basket-weave microstructure characterization. The grains of the sample prepared using island scanning are significantly finer than that prepared by orthogonal successive scanning due to faster cooling during deposition. However, the relative density of the sample prepared using island scanning was slightly smaller due to the concentration of lack-of-fusion pores at the overlap zone of the island. Tensile testing at room temperature indicates that the ultimate tensile strength and yield strength of the sample prepared using island scanning is enhanced due to finer grains, while the ductility of the sample is weakened due to defects.
PubDate: 2019-09-01

• Solid-State Diffusion Bonding of Nb SS /Nb 5 Si 3 Composite Using Ni/Al
and Ti/Al Nanolayers
• Abstract: Diffusion bonding of refractory Nb–Si-based alloy was performed with Ni/Al and Ti/Al nanolayers under the condition of 1473 K/30 MPa/60 min. The NbSS/Nb5Si3 in situ composite with the nominal composition of Nb–22Ti–16Si–3Cr–3Al–2Hf was used as the parent material. The joint microstructures were examined by using a scanning electron microscope equipped with an X-ray energy dispersive spectrometer. Shear test was conducted for the bonded joints at room temperature. Within the joint bonded with Ni/Al multilayer, element diffusion occurred between the base metal and the nanolayer, with the reaction products of AlNb2 + Ni3Al, NiAl and AlNi2Ti phases. The average shear strength was 182 MPa. While using Ti/Al multilayer, the interface mainly consisted of TiAl, (Ti,Nb)Al and (Ti,Nb)2Al phases, and the corresponding joints exhibited an increased strength of 228 MPa. In this case, the fracture mainly took place in the TiAl phase and presented a typical brittle characteristic.
PubDate: 2019-09-01

• Residual Stress Removal Under Pulsed Electric Current
• Abstract: The effect of a pulsed electric current on the residual stress evolution of metal materials has been investigated. It was found that the surface and internal residual stresses in the as-quenched samples were reduced dramatically by electropulsing. A large number of experimental data show that the residual stress reduction is proportional to the initial residual stress and related to the material properties and electropulsing parameters. Under the combined actions of drift electrons, Joule heating, and residual stress, the dislocation mobility was enhanced, resulting in plastic strain and the decrease in residual stress. Drift electrons played a unique role in the electropulsing treatment, acting as an additional force pushing dislocations forward. The dislocations ultimately accumulated at a grain boundary, forming a parallel arrangement. Finally, the phenomenological equation of the residual stress evolution under electropulsing was derived from the experimental data.
PubDate: 2019-08-16

• Thermo-mechanical Analysis of Friction Stir Welding: A Review on Recent
• Abstract: In recent studies, critical research interest exists in the thermo-mechanical analysis of the friction stir welding (FSW) process by numerical simulation. In this review, the thermo-mechanical analysis for FSW is overviewed regarding the computational approaches, the heat generation, the temperature, and the material flow behavior. Current concerns, challenges, and opportunities in current studies are discussed considering the application of the thermo-mechanical analysis. Generally, larger computational scale and better computational efficiency are required to allow better spatial resolution in future analysis. The concepts and approaches demonstrated in the thermo-mechanical analysis for FSW open up quantitative prospects for the design of the FSW process.
PubDate: 2019-08-16

• Effect of Zener–Hollomon Parameter on Microstructure and Mechanical
Properties of Copper Subjected to Friction Stir Welding
• Abstract: In this work, the influence of the Zener–Hollomon (Z) parameter on the microstructure and mechanical properties of copper subjected to friction stir welding (FSW) was investigated. Liquid N2 cooling was conducted to control the cooling rate after the FSW. The obtained results demonstrate that the Z parameter was dependent on the tool rotation rate during the FSW, i.e., a higher tool rotating rate resulted in a lower Z parameter. The grain size in the stir zone decreased with the increase in the Z parameter. The relationship between the yield strength and the Z parameter is established as σ0.2 = σ0 + kZn. This relationship exhibited two different plots under the conditions of air cooling and liquid N2 cooling. Even at a similar Z parameter, a significant yield strength difference occurred because massive dislocations, which were caused by the prevention of the post-annealing effect, were maintained in the stir zone. This study suggests that the influence of the post-annealing effect should not be neglected when analyzing the relationship between the Z parameter, microstructure, and mechanical properties.
PubDate: 2019-08-16

• Microstructural Evolution, Mechanical Properties and Thermal Stability of
• Abstract: The microstructural evolution of pure nickel treated by deep rolling (DR) technique with different indent depths was investigated by means of optical microscopy and transmission electron microscopy. The surface roughness, hardness and residual stress distribution along the depth from surface were measured. Moreover, the DR-treated sample was annealed at temperatures from 300 to 700 °C for 2 h. The results reveal that dislocation movements are the fundamental mechanisms of gradient grain refinement during the DR process. With increasing indent depth of the DR, the gradient microhardness on the cross section of sample significantly increases, the maximum compressive residual stress decreases, and the affecting region of residual stress increases. The results of thermal stability depict that the microstructure can be stable as temperature up to 300 °C, and the abnormal grain growth and annealing twins are observed at 600 °C.
PubDate: 2019-08-01

• Quasi-In-Situ EBSD Observation of the Orientation Evolution in
Polycrystalline Tantalum During Rolling Deformation
• Abstract: The evolution of crystallographic orientation of polycrystalline tantalum (Ta) during rolling was characterized by electron backscatter diffraction technique in a quasi-in-situ way, and the microstructure and microtexture before and after the deformation were characterized and analyzed, respectively. In the specimen, 164 individual grains were exacted singly from the testing region and their corresponding orientations were reconstructed and analyzed, respectively. Results show that the heterogeneous deformation in a grain can be reflected by the accidented surface microstructure. Moreover, the orientations close to {111} orientations came closer to the {111} corner, while the orientation evolution is more complicated for the orientations close {100} corner, indicating that the evolution of these orientations close to {100} corner seemed to be irregular.
PubDate: 2019-08-01

• Hot Deformation Behavior and Hardness of a CoCrFeMnNi High-Entropy Alloy
with High Content of Carbon
• Abstract: A CoCrFeMnNi high-entropy alloy with a high content of carbon was synthesized, and its hot deformation behavior was studied at the temperatures 800–1000 °C at the strain rates ranging from 0.001 to 0.1 s−1. As-prepared alloy is a face-centered cubic-structured solid solution, with a large amount of carbides residing at grain boundaries. True stress–strain curves were employed to develop the constitutive equation of apparent activation energy. The apparent activation energy (Q) was found to be 423 kJ mol−1, indicating a dynamic flow softening behavior. The size of dynamic recrystallized (DRXed) grains increases with increasing the temperature or decreasing the strain rate. A processing map was sketched on the basis of the flow stress. The temperature range of 900–1000 °C and 10−3–10−2.6 s−1 strain rate were found to be the optimum hot-forging parameter. With increasing temperature or decreasing strain rate, the volume fraction of fine carbides (≤ 1 μm) increases. A lot of coarse carbides can be found in the matrix after deformation at 800 °C, which leads to a high hardness value of 345 HV. The carbides after deformation at 1000 °C are mainly nano-sized M7C3 and M23C6, which can promote the nucleation of DRX.
PubDate: 2019-08-01

• Effect of Deep Sea Pressures on the Corrosion Behavior of X65 Steel in the
Artificial Seawater
• Abstract: The corrosion behaviors of X65 steel in the artificial seawater at different hydrostatic pressures are investigated by potentiodynamic polarization measurements, electrochemical impedance spectroscopy measurements and weight loss measurements. The corroded morphologies and the corrosion products are also investigated by scanning electron microscopy, X-ray diffraction analysis and Raman analysis. The results show that the corrosion current increases as the hydrostatic pressure increases. The charge transfer resistance decreases as the hydrostatic pressure increases. The corrosion products are mainly composed of γ-FeOOH and Fe3O4 at the atmospheric pressure, while the main components are γ-FeOOH, Fe3O4, and γ-Fe2O3 at the high pressure. The hydrostatic pressure accelerates the corrosion of X65 steel due to its effect on the chemical and physical properties of corrosion products, including the promoted reduction of γ-FeOOH and the wider and deeper cracks on the corrosion products layer.
PubDate: 2019-08-01

• Effects of Ni Content and Ball Milling Time on the Hydrogen Storage
Thermodynamics and Kinetics Performances of La–Mg–Ni Ternary Alloys
• Abstract: The effects of Ni content and ball milling time on the hydrogen storage thermodynamics and kinetics performances of as-milled $${\text{La}}_{5} {\text{Mg}}_{95 - x} {\text{Ni}}_{x} \left( {x = 5, \, 10, \, 15} \right)$$ ternary alloys have been investigated. The evolution of microstructure and phase of experimental alloys in the absorption/desorption process has been characterized by XRD, SEM and HRTEM. The hydrogen storage kinetics and thermodynamics performances and PCI curves have been tested using the Sievert apparatus. It is found that the rising of Ni content remarkably improves the hydrogen storage kinetic performance, but reduces hydrogen storage capacity. And with the increase in milling time, hydrogen desorption activation (Ea) value decreases firstly and then increases; the minimum value is 47.6 kJ/mol, and the corresponding milling time is 10 h for La5Mg85Ni10 alloy. As for the thermodynamics properties, the hydrogenation enthalpy (ΔH) and hydrogenation entropy (ΔS) both decrease firstly and then increase with the rising of Ni content and milling time. The composite La5Mg85Ni10 alloy milled for 10 h exhibits the best thermodynamics and kinetics performances, the lowest Ea of 47.6 kJ/mol, absorption of 5.4 wt.% within 5 min and desorption of 5.2 wt.% within 3 min at 360 °C and the lowest ΔH and ΔS of 72.1 kJ/mol and 123.2 J/mol/K.
PubDate: 2019-08-01

• Microstructure, Mechanical Properties, and Corrosion Behavior of
MoNbFeCrV, MoNbFeCrTi, and MoNbFeVTi High-Entropy Alloys
• Abstract: The development of high-entropy alloys (HEAs) has stimulated an ever-increasing interest from both academia and industries. In this work, three novel MoNbFeCrV, MoNbFeCrTi, and MoNbFeVTi HEAs containing low thermal neutron absorption cross section elements were prepared by vacuum arc melting. The microstructure, mechanical properties, and corrosion behaviors were investigated. A dominant body-centered cubic (BCC) phase was present in all these three HEAs. In addition, an ordered Laves phase was found to be another major phase in both MoNbFeCrV and MoNbFeCrTi alloys, whereas an ordered BCC (B2) phase was observed in the MoNbFeVTi alloy. The phase formation in these three alloys was discussed. It is found that the formation of the secondary phase in these alloys is mainly ascribed to the large atomic size difference and electronegativity difference. All the three HEAs show high hardness, high yield strength but limited plasticity. Moreover, the MoNbFeCrV, MoNbFeCrTi and MoNbFeVTi alloys exhibit excellent corrosion resistance in both deaerated 1 mol/L NaCl and 0.5 mol/L H2SO4 solutions at room temperature. However, further composition adjustment and/or thermomechanical processing is required to enhance the mechanical properties of the three alloys.
PubDate: 2019-07-11

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