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Acta Metallurgica Sinica (English Letters)
[SJR: 0.525] [H-I: 18] [5 followers] Follow

Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1006-7191 - ISSN (Online) 2194-1289
Published by Springer-Verlag

[2355 journals]

Influence of Surface Finishing on High-Temperature Oxidation of AISI Type
444 Ferritic Stainless Steel Used in SOFC Stacks
- Authors: Valeria Bongiorno; Paolo Piccardo; Simone Anelli; Roberto Spotorno
  Pages: 697 - 711
  Abstract: This research is focused on the study of the samples, approximatively 15 × 30 mm2 sized, that were mechanically cut from two sheets (0.4 and 0.2 mm thick, respectively) of AISI 444 Type ferritic stainless steel (FSS) (DIN 1.4521, Eu designation X2CrMoTi18-2); this material was in the ‘as-rolled’ state. Part of these specimens were treated superficially on one side using abrasive SiC papers with different average grit sizes (i.e., 46.2, 30.2, 18.3 μm) and diamond suspension (up to 1 μm) in order to obtain various surface roughness. Both the ‘as-rolled’ and superficially treated samples were then aged in a muffle furnace in static air according to a thermal cycle corresponding to the curing phase of an experimental glass used as sealing in the solid oxide fuel cell stacks. After aging, the chemical compositions and morphological peculiarities of the scale formed depending on the thickness of the samples and their surface state were studied by scanning electron microscopy, energy-dispersive spectroscopy, micro-Raman spectroscopy, bright field light optical microscopy. The obtained results show that all scales formed consist of an inner Cr2O3 subscale and an outer (Mn,Cr)3O4 spinel layer; the relationship between FSS grain size and scale microstructural features is consistent on the samples with mirror-like surface only; the scale thicknesses on SiC grinded samples are comparable; the scales covering the ‘as-rolled’ surfaces are morphologically similar to those grown on the surfaces finished with the 30.2 and 18.3 μm SiC papers, and their thicknesses show an intermediate situation between the abraded and the mirror-like specimens. The last described characteristics depend mainly on the surface and microstructural peculiarities resulting from the rolling process.
  PubDate: 2017-08-01
  DOI: 10.1007/s40195-017-0543-1
  Issue No: Vol. 30, No. 8 (2017)
Corrosion and Cavitation Erosion Behaviors of Two Marine Propeller
Materials in Clean and Sulfide-Polluted 3.5% NaCl Solutions
- Authors: Qi-Ning Song; Nan Xu; Ye-Feng Bao; Yong-Feng Jiang; Wei Gu; Yu-Gui Zheng; Yan-Xin Qiao
  Pages: 712 - 720
  Abstract: The corrosion and cavitation erosion behaviors of two main materials for ship propellers, i.e., nickel–aluminum bronze (NAB) and manganese–nickel–aluminum bronze (MAB) were investigated in a clean and sulfide-polluted 3.5% NaCl solutions. The presence of sulfide increased the corrosion damage of both NAB and MAB by rendering the corrosion product film thicker, more porous and less protective. For MAB, the formation of Fe oxides/sulfides within the corrosion product film may reduce the film compactness and responsible for the lower corrosion resistance, compared with NAB. The presence of sulfide caused the occurrence of more severe corrosion on the surface and therefore further enhanced the cavitation erosion damage. Compared with the result in the clean solution, the cavitation–erosion mass loss rate was raised by a factor of about 11.88% for MAB, and 58.6% for NAB. For NAB, the mechanical erosion dominated the damage in the clean solution, while the cavitation erosion synergy made a significant contribution to the overall damage in the sulfide-polluted solution. For MAB, it was the mechanical damage that contributed mainly to the cavitation erosion damage in both solutions. The exfoliation of large-sized κ phase and the cleavage rupture of β phases resulted in lower cavitation erosion resistance of MAB, compared with NAB.
  PubDate: 2017-08-01
  DOI: 10.1007/s40195-017-0602-7
  Issue No: Vol. 30, No. 8 (2017)
Comparative Study of Bypass-Current MIG Welded–Brazed
Aluminum/Galvanized Steel and Aluminum/Stainless Steel
- Authors: Yu-Gang Miao; Guang-Yu Chen; Peng Zhang; Duan-Feng Han
  Pages: 721 - 730
  Abstract: A bypass-current metal inert-gas welding–brazing technology has been developed to join aluminum/galvanized steel and aluminum/stainless steel. Microstructure, intermetallic compounds and hardness distribution of the joints were studied by optical microscopy, scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction analysis and microhardness tests. Comparative study on both types of joints was carried out. During aluminum to galvanized steel assembling, finer seam was obtained under a more stable process. A uniform interfacial reaction layer with a thickness of 2–4 μm was formed. During aluminum to stainless steel assembling, an uneven interfacial reaction layer with a thickness of 5–45 μm was formed. Intermetallic compounds at the interface of aluminum/galvanized steel were identified as Fe–Al–Si–Zn complex phases, while Fe–Al–Cr–Ni complex phases were found at the aluminum/stainless steel interface. Microhardness of interfacial layer increases rapidly within reaction layer due to possible brittle intermetallic compounds.
  PubDate: 2017-08-01
  DOI: 10.1007/s40195-017-0578-3
  Issue No: Vol. 30, No. 8 (2017)
Preliminary Study on Porous High-Manganese 316L Stainless Steel Through
Physical Vacuum Dealloying
- Authors: Yibin Ren; Jun Li; Ke Yang
  Pages: 731 - 734
  Abstract: In this study, porous stainless steel was prepared successfully by physical vacuum dealloying method. The based alloy is high-manganese 316L-50Mn alloy. The porous high-manganese 316L stainless steel showed a three-dimensional continuous porous structure with 1–2 μm pore size. Temperature was the key factor for the physical dealloying process to produce porous stainless steel, and the optimized treatment temperature was between 800 and 850 °C for the high-manganese 316L-50Mn alloy.
  PubDate: 2017-08-01
  DOI: 10.1007/s40195-017-0600-9
  Issue No: Vol. 30, No. 8 (2017)
Characterization of Prealloyed Ti–6Al–4V Powders from EIGA and PREP
Process and Mechanical Properties of HIPed Powder Compacts
- Authors: Rui-Peng Guo; Lei Xu; Bernie Ya-Ping Zong; Rui Yang
  Pages: 735 - 744
  Abstract: Prealloyed Ti–6Al–4V powders were prepared by electrode induction melting gas atomization (EIGA) and plasma rotating electrode process (PREP) in this work. A comparative study of EIGA and PREP powders for hot isostatic pressing (HIPing) compaction was conducted. Characterization of important technological parameters such as particle size distribution, powder surface morphology and flowability was carried out. Microstructure and mechanical properties of Ti–6Al–4V powder compacts HIPed from EIGA and PREP powders were also investigated. The results showed that the EIGA powder has a finer average particle size and higher tap density, while the PREP powder has better flowability and less pores. Micropores can be observed in heat-treated EIGA powder compacts by X-ray tomography and the porosity was found to be about 0.02%. There are no micropores (≥4 μm) to be detected in heat-treated PREP powder compacts. Transgranular fracture mode as well as micropores contributes to the scatter in fatigue property of heat-treated PREP powder compacts. The respective advantages and disadvantages of both EIGA and PREP powders for producing Ti-based complex parts through HIPing were also discussed.
  PubDate: 2017-08-01
  DOI: 10.1007/s40195-017-0540-4
  Issue No: Vol. 30, No. 8 (2017)
Quantitative Phase Field Simulation of α Particle Dissolution in
Ti–6Al–4V Alloys Below β Transus Temperature
- Authors: Mei Yang; Gang Wang; Tao Liu; Wen-Juan Zhao; Dong-Sheng Xu
  Pages: 745 - 752
  Abstract: A quantitative phase field method of multi-component diffusion-controlled phase transformations coupled with the Kim–Kim–Suzuki model was applied to study the effect of initial particle size distribution (PSD) in 3D and space distribution in 2D on dissolution of α particles in Ti–6Al–4V alloy below β transus temperature in real time and length scale. The thermodynamic and mobility data were obtained from Thermo-Calc and DICTRA softwares, respectively. The results show that the volume fractions of α particles decay with time as: \( f = f_{\text{eq}} + (f_{0} - f_{\text{eq}} )\exp ( - Kt^{n} ) \) for four cases of PSD. The sequence of dissolution kinetics from fast to slow is: uniform PSD, normal PSD, lognormal PSD and bimodal PSD. The space distribution is found to be a major factor affecting the dissolution kinetics and the microstructures. When the distance of the particles is less than critical value, the dissolution rates reduce with the decrease in distance. The Al and V concentration fields around the particles appear more obvious soft impingement.
  PubDate: 2017-08-01
  DOI: 10.1007/s40195-017-0562-y
  Issue No: Vol. 30, No. 8 (2017)
Influence Factors of Aluminum–Slag Interfacial Reaction Under
Electric Field
- Authors: Xin-Yu Lv; An-Ping Dong; Jun Wang; Da Shu; Bao-De Sun
  Pages: 753 - 761
  Abstract: The interfacial reaction between aluminum melt and molten slag under an electric field plays a significant role in aluminum electro-slag refining. Here we studied this interfacial reaction within 680 and 820 °C under an electric field between 0 and 9 V. The evolution of aluminum composition was analyzed by inductively coupled plasma atomic emission spectroscopy. The dominant factor during the interfacial reaction was identified through orthogonal experiments, in which the slag-to-aluminum mass ratio, initial silicon concentration, electric voltage, reaction time, and temperature were selected as the influence factors. The greatest influence factor on the interfacial reaction was found to be the reaction time. Also, single-factor experiments revealed that the reaction kinetic processes largely obeyed an irreversible kinetic model, and the silicon removal efficiency was enhanced by increasing the voltage and slag/metal ratio.
  PubDate: 2017-08-01
  DOI: 10.1007/s40195-017-0574-7
  Issue No: Vol. 30, No. 8 (2017)
Influence of Fe Addition on Phase Transformation, Microstructure and
Mechanical Property of Equiatomic NiTi Shape Memory Alloy
- Authors: Ya-Nan Zhao; Shu-Yong Jiang; Yan-Qiu Zhang; Yu-Long Liang
  Pages: 762 - 770
  Abstract: Based on equiatomic nickel and titanium, three kinds of NiTiFe alloys with a nominal chemical composition of Ni49Ti49Fe2, Ni48Ti48Fe4 and Ni47Ti47Fe6 (at.%), respectively, have been designed to investigate the influence of the addition of Fe element on phase transformation, microstructure and mechanical property of equiatomic NiTi shape memory alloy. The microstructures of three kinds of NiTiFe alloys are characterized by the equiaxed grains instead of the dendrites. Consequently, some Ti2Ni precipitates are found to distribute in the grains interior and at the grain boundaries. The content of Fe element has an important influence on mechanical property of NiTiFe alloy. With increasing content of Fe element, the strength of NiTiFe alloy increases substantially, but the plasticity decreases sharply. It can be concluded that precipitation strengthening and solution strengthening play a significant role in enhancing the strength of NiTiFe alloy. In the case of three NiTiFe alloys, neither martensitic transformation nor reverse transformation can be observed in the range from −150 to 150 °C. On the one hand, the phase transformation temperature is probably out of the scope of the present experimental temperature. On the other hand, the addition of Fe element probably suppresses first-order martensitic transformation or reverse transformation, and consequently the second-order-like phase transformation from an incommensurate stage to a commensurate stage can probably take place.
  PubDate: 2017-08-01
  DOI: 10.1007/s40195-017-0584-5
  Issue No: Vol. 30, No. 8 (2017)
Secondary Precipitation Behavior of Nitride in the Electro-slag Remelted
Structure of Alloy 690
- Authors: Min Wang; Bo Chen; Xian-Chao Hao; Ying-Che Ma; Kui Liu
  Pages: 771 - 780
  Abstract: The precipitation and evolution of secondary nitrides (S-nitrides) in the Alloy 690 electro-slag remelted (ESR) structure were investigated. Experimental results indicate that S-nitrides precipitated in the interdendritic region of the ESR structure at temperatures higher than 1100 °C. S-nitrides could spread throughout the entire interdendritic area after sufficient exposure, and they were more numerous and much finer than primary nitrides. Furthermore, after studying the evolution of S-nitride particles at 1100, 1200 and 1300 °C, it was determined that the precipitation of S-nitrides was controlled by the diffusion of nitrogen. In addition, by investigating the elemental segregation of ESR structure and calculating critical Ti concentrations, S-nitride precipitation was found to be thermodynamically inevitable in the Alloy 690 ESR structure.
  PubDate: 2017-08-01
  DOI: 10.1007/s40195-017-0541-3
  Issue No: Vol. 30, No. 8 (2017)
Tribological Characterization of Hybrid Metal Matrix Composites Processed
by Powder Metallurgy
- Authors: M. Megahed; M. A. Attia; M. Abdelhameed; A. G. El-Shafei
  Pages: 781 - 790
  Abstract: Aluminum (Al)-based aluminum oxide (Al2O3) and silicon carbide (SiC) particles hybrid metal matrix composites were processed by powder metallurgy technique, followed by sintering at 500 °C and then hot extrusion. The tribological properties of these composites with different weight fractions of Al2O3 and SiC were investigated; extrusion process significantly reduces the extent of porosity after cold compaction and sintering processes. Hybridization of the two reinforcements improved hardness and wear resistance of the composites. With an increase in SiC content, hardness was increased and consequently the wear resistance was enhanced also. Scanning electron microscopy observations show a better interfacial bond between matrix and reinforcements and a better distribution of the reinforcements.
  PubDate: 2017-08-01
  DOI: 10.1007/s40195-017-0568-5
  Issue No: Vol. 30, No. 8 (2017)
Experiment and Simulation for Rolling of Diamond–Cu Composites
- Authors: Yun-Long Wang; Kai-Kun Wang; Yu-Wei Wang; Guang-Chen Li
  Pages: 791 - 800
  Abstract: We demonstrate an innovative preparation approach of diamond/Cu composites by powder-in-tube technique and rolling. A small copper tube was loaded with Ti- and Cu-coated diamond particles, and then the diamond particles were combined with Cu matrix by composite rolling. The morphology and element distribution of the interface between diamond and Cu were determined by scanning electron microscopy and energy-dispersive spectrometer. Finite element method (FEM) simulation was used to analyze the rolling process associated with experiment by DEFORM-3D. The final experimental results showed that homogeneous distribution of diamond particles could be observed in the center layer of the composites. According to the contrast experiments, the sample, whose diamond particle size is 0.12–0.15 mm and thickness of pre-rolling is 1.2 mm, showed relatively complete morphologies and homogeneous distribution. Experimental results indicated a poor efficacy of excessive rolling reduction. The thermal conductivity of the composites is about 453 W (m K)−1 by theoretical calculation. For FEM simulation, rolling strain and temperature field of the composites were simulated by DEFORM-3D. Simulation results were interpreted, and numerical results verified the reliability of the model. The simulation predicted that the local area of large strain, indicative of the strain along the thickness direction, could be intensified by adding diamond particles.
  PubDate: 2017-08-01
  DOI: 10.1007/s40195-017-0561-z
  Issue No: Vol. 30, No. 8 (2017)
Influence of Silver Contents on the Tribological Properties of Ni-Based
Self-Lubricating Coatings by Atmospheric Plasma Spraying
- Authors: Bo Li; Jun-Hong Jia; Yi-Min Gao; Hong-Jian Guo; Min-Min Han; Wen-Zhen Wang
  Pages: 801 - 808
  Abstract: The NiCrAlY–Mo–Ag composite coatings were prepared by atmospheric plasma spraying. The tribological properties of the composite coatings were investigated from 25 to 900 °C in details. The tribo-layer formed on the worn surface of the composite coatings and influenced the tribological properties at different temperatures. The addition of silver could effectively decrease the friction coefficient and wear rate of the coatings at the wide range of temperature. The rubbing process could form the nickel molybdate and promote the formation of silver molybdate within the worn surfaces at high temperature. The synergistic lubricating effects of nickel molybdate and silver molybdate are attributed to the improvement of the tribological properties of coatings at high temperature.
  PubDate: 2017-08-01
  DOI: 10.1007/s40195-017-0573-8
  Issue No: Vol. 30, No. 8 (2017)
Fabrication of Fullerene-Reinforced Aluminum Matrix Nanocomposites
- Authors: Hamed Asgharzadeh; Hamid Faraghi; Hyoung Seop Kim
  Abstract: Fullerene-reinforced Al matrix nanocomposites were fabricated by high-energy mechanical milling followed by consolidation through hot extrusion or high-pressure torsion (HPT). The results indicate that a relatively homogeneous microstructure consisting of elongated, micrometer-sized Al grains is formed in the hot-extruded specimens. However, the microstructure is not uniform along the radius of the HPT disks, which includes coarse grains near the center of the disk and ultrafine grains in the middle and along the edge of the specimen. Microstructural evaluations of the HPT disks indicate that Al grain refinement occurs due to the addition of fullerene, as grain size is reduced to 60 nm from 118 nm. The formation of the harmful aluminum carbide phase is not detected during the fabrication of Al/C60 nanocomposites. The hardness, yield stress, and ultimate tensile strength of the Al-2 vol.% C60 nanocomposites are about 27–160% higher than those of the monolithic Al samples, revealing the effective strengthening of fullerene particles in Al matrix. Moreover, mechanical properties of the Al/fullerene nanocomposites are significantly enhanced (59–272%) by utilizing HPT in comparison to hot-extruded specimens due to their much finer Al grain structure. The reduction in the number and the size of the dimples, as well as the formation of smooth regions on the tensile fracture surface of Al/C60, results in their overall lower ductility compared to monolithic Al.
  PubDate: 2017-07-14
  DOI: 10.1007/s40195-017-0629-9
Molecular Dynamics Simulations and Experimental Investigations of Atomic
Diffusion Behavior at Bonding Interface in an Explosively Welded Al/Mg
Alloy Composite Plate
- Authors: Ting-Ting Zhang; Wen-Xian Wang; Jun Zhou; Xiao-Qing Cao; Rui-Shan Xie; Yi Wei
  Abstract: In this study, 6061 aluminum alloy and AZ31B magnesium alloy composite plate was fabricated through explosive welding. Molecular dynamics (MD) simulations were conducted to investigate atomic diffusion behavior at bonding interface in the Al/Mg composite plate. Corresponding experiments were conducted to validate the simulation results. The results show that diffusion coefficient of Mg atom is larger than that of Al atom and the difference between these two coefficients becomes smaller with increasing collision velocity. The diffusion coefficient was found to depend on collision velocity and angle. It increases linearly with collision velocity when the collision angle is maintained constant at 10° and decreases linearly with collision angle when the collision velocity is maintained constantly at 440 m/s. Based on our MD simulation results and Fick’s second law, a mathematical formula to calculate the thickness of diffusion layer was proposed and its validity was verified by relevant experiments. Transmission electron microscopy and energy-dispersive system were also used to investigate the atomic diffusion behavior at the bonding interface in the explosively welded 6061/AZ31B composite plate. The results show that there were obvious Al and Mg atom diffusion at the bonding interface, and the diffusion of magnesium atoms from magnesium alloy plate to aluminum alloy plate occurs much faster than the diffusion of aluminum atoms to the magnesium alloy plate. These findings from the current study can help to optimize the explosive welding process.
  PubDate: 2017-07-13
  DOI: 10.1007/s40195-017-0628-x
Crystallographic Texture Evolution of γ′-Fe 4 N and Its Influences on
Tribological Property of Nitrided Steel
- Authors: Yi-Xue Wang; Mu-Fu Yan; Zhao-Bo Chen; Cheng-Song Zhang; Yuan You
  Abstract: The crystallographic texture of γ′-Fe4N in compound layer and its influences on the tribological properties of nitrided steel 38CrMoAl are investigated in the study. The preferred orientation of (200)γ′ is produced by low-temperature nitriding in atmosphere with low nitrogen–hydrogen ratio and increases with the nitriding time. The preferred orientation of (220)γ′ appears after 72 h cyclic nitriding. The orientation relationships (0001)ε//(101)α′ and [110]ε//[111]α′, (111)γ′//(0001)ε and \(\left[ {011} \right]_{{\gamma^{\prime } }} //\left[ {1\overline{2} 10} \right]_{\varepsilon }\) , (200)γ′//(110)α′ and [011]γ′//[111]α′, as well as \(\left( {1\overline{1} 03} \right)_{\varepsilon } //\left( {220} \right)_{{\gamma^{\prime } }}\) and \(\left[ {0100} \right]_{\varepsilon } //\left[ {1\overline{1} 0} \right]_{{\gamma^{\prime } }}\) are established by first-principles method. The misfit of interatomic distance (δ), determining the phase transition resistance, is calculated. Accordingly, two reaction pathways during nitriding, α′→γ′ and α′→ε→γ′, are assumed, which determines the preferred orientations of γ′-Fe4N. Results of wear tests demonstrate that the specimen with preferred orientation of (200)γ′ exhibits lower frictional coefficient and lower wear rate in comparison with the specimen with (220)γ′ preferred orientation. (111)γ′ texture usually relates to the lower frictional coefficient but higher wear rate due to the main slip system parallel to the sliding plane. Therefore, the (200)γ′ preferred orientation has a positive significance in improving the wear properties of steels.
  PubDate: 2017-07-12
  DOI: 10.1007/s40195-017-0621-4
Origin of Insignificant Strengthening Effect of CNTs in T6-Treated
CNT/6061Al Composites
- Authors: Ke Zhao; Zhen-Yu Liu; Bo-Lyu Xiao; Ding-Rui Ni; Zong-Yi Ma
  Abstract: Carbon nanotube (CNT)-reinforced 6061Al (CNT/6061Al) composites were fabricated via powder metallurgy combined with friction stir processing (FSP). CNTs were dispersed after FSP and accelerated the precipitation process of the CNT/6061Al composites. However, the strengthening effect of CNTs on the T6-treated materials was insignificant, while the composites under the FSP and solution treatment conditions exhibited increased strength compared to the matrix. Precipitate-free zones (PFZs) were detected around CNTs in the T6-treated CNT/6061Al composites, and a model was proposed to describe the effect of PFZs on strength. The calculations indicated that the strength of PFZs was similar to that of the T6-treated 6061Al. As a result, the strengthening effect of CNTs on the T6-treated CNT/6061Al composites was insignificant.
  PubDate: 2017-07-08
  DOI: 10.1007/s40195-017-0626-z
Non-isothermal Crystallization Kinetics and Isothermal Crystallization
Kinetics in Supercooled Liquid Region of Cu–Zr–Al–Y Bulk Metallic
Glass
- Authors: Ke Yang; Xin-Hui Fan; Bing Li; Yan-Hong Li; Xin Wang; Xuan-Xuan Xu
  Abstract: The crystallization kinetics of Cu43Zr48Al9 and (Cu43Zr48Al9)98Y2 bulk metallic glasses in non-isothermal and isothermal conditions was studied by differential scanning calorimetry. In the non-isothermal and isothermal modes, the average activation energy of (Cu43Zr48Al9)98Y2 is larger than that of Cu43Zr48Al9, meaning the higher stability against crystallization of (Cu43Zr48Al9)98Y2. In addition, the average activation energies for Cu43Zr48Al9 and (Cu43Zr48Al9)98Y2 calculated using Arrhenius equation in isothermal mode are larger than the values calculated by Kissinger–Akahira–Sunose method in non-isothermal mode, indicating that the energy barrier is higher in isothermal mode. The Johnson–Mehl–Avrami model was used to analyze the crystallization kinetics in the non-isothermal and isothermal modes. The Avrami exponent n for Cu43Zr48Al9 is above 2.5, indicating that the crystallization is mainly determined by a diffusion-controlled three-dimensional growth with an increasing nucleation rate, while the Avrami exponent n for (Cu43Zr48Al9)98Y2 is in the range of 1.5–2.5 in the non-isothermal mode, implying that the crystallization is mainly governed by diffusion-controlled three-dimensional growth with decreasing nucleation rate. Finally, the Avrami exponents n for Cu43Zr48Al9 and (Cu43Zr48Al9)98Y2 are different in the non-isothermal and isothermal conditions, which imply different nucleation and growth behaviors during the crystallization processes.
  PubDate: 2017-07-07
  DOI: 10.1007/s40195-017-0625-0
Stress Study on CrN Thin Films with Different Thicknesses on Stainless
Steel
- Authors: Di Fan; Hao Lei; Chao-Qian Guo; Dong-Li Qi; Jun Gong; Chao Sun
  Abstract: The reliability of a substrate curvature-based stress measurement method for CrN thin films on substrate with fluctuant surface was discussed. The stress error led by the ignorance of substrate thermal deformation was studied. Results showed that this error could be as large as several hundred MPa under general deposition conditions. Stress in the CrN thin films with different thicknesses ranging from 110 to 330 nm on stainless steel was studied by this method, in comparison with conventional results on silicon wafer. The thin films’ morphology and structure were investigated and related to the film stress. A significant result of the comparison is that stress evolution in the thin films on steel obviously differs from that on silicon wafer, not only because the two substrates have different coefficients of thermal expansion, which provokes thermal stress, but also the considerable discrepancy in the thin films’ grain coarsening rate and structure that induce different intrinsic stresses.
  PubDate: 2017-07-07
  DOI: 10.1007/s40195-017-0620-5
Synthesis of Co 3 O 4 Nanoparticles Wrapped Within Full Carbon Matrix as
an Anode Material for Lithium Ion Batteries
- Authors: Subhalaxmi Mohapatra; Shantikumar V. Nair; Alok Kumar Rai
  Abstract: A facile polyol-assisted pyro-synthesis method was used to synthesize Co3O4 nanoparticles embedded into carbon matrix without using any conventional carbon source. The surface analysis by scanning electron microscopy showed that the Co3O4 nanoparticles (~20 ± 5 nm) are tightly enwrapped within the carbon matrix. CHN analysis determined the carbon content was only 0.11% in the final annealed sample. The Co3O4@carbon exhibited high capacities and excellent cycling performance as an anode at various current rates (such as 914.4 and 515.5 mAh g−1 at 0.25 and 1.0 C, respectively, after 50 cycles; 318.2 mAh g−1 at a high current rate of 5.0 C after 25 cycles). This superior electrochemical performance of the electrode can be attributed to the various aspects, such as, (1) the existence of carbon matrix, which acts as a flexible buffer to accommodate the volume changes during Li+ ion insertion/deinsertion and facilitates the fast Li+ and electron transfer and (2) the anchoring of Co3O4 nanoparticles within the carbon matrix prevents particles agglomeration.
  PubDate: 2017-07-06
  DOI: 10.1007/s40195-017-0622-3
Microstructure Characteristics and Mechanical Properties of Nb-17Si-23Ti
Ternary Alloys Fabricated by In Situ Reaction Laser Melting Deposition
- Authors: Wei Liu; Hua-Ping Xiong; Neng Li; Shao-Qing Guo; Ren-Yao Qin
  Abstract: Fabrication of ternary Nb–17Si–23Ti alloys was attempted by in situ reaction laser melting deposition (LMD) with dual powder feeding method from Nb-28 at.% Ti powder mixture and pure Si powder. The microstructures of the as-deposited alloys were examined with scanning electronic microscope, and the phase constituents were analyzed by X-ray energy-dispersive spectrometer and X-ray diffraction. Furthermore, the effect of laser power on microstructure characteristics, microhardness and indentation fracture toughness was also investigated. The in situ reaction LMD process resulted in remarkable refinement of the microstructure. The as-deposited samples mainly consisted of NbSS, metastable (NbTi)3Si and Ti-rich NbSS. With the increase in the laser power from 1000 to 2000 W, the NbSS morphology changed from discontinuous dendritic to near equiaxed, but the Ti-rich NbSS phase tended to vanish. Furthermore, with the increase in the laser power, the microhardness of as-deposited samples increased from 822 to 951 HV, while the indentation fracture toughness was improved from 12.3 to 14.1 MPa m1/2. The corresponding mechanism is also discussed.
  PubDate: 2017-07-06
  DOI: 10.1007/s40195-017-0619-y