Strted in 1985 Monthly
ISSN 1005-0302
CN 21-1315/TG
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Anaerobic microbiologically influenced corrosion mechanisms interpreted using bioenergetics and bioelectrochemistry: A review
Yingchao Li, Dake Xu, Changfeng Chen, Xiaogang Li, Ru Jia, Dawei Zhang, Wolfgang Sand, Fuhui Wang, Tingyue Gu
J. Mater. Sci. Technol.    2018, 34 (10): 1713-1718.   DOI: 10.1016/j.jmst.2018.02.023
Abstract   HTML PDF (1654KB)  

Microbiologically influenced corrosion (MIC) is a major cause of corrosion damages, facility failures, and financial losses, making MIC an important research topic. Due to complex microbiological activities and a lack of deep understanding of the interactions between biofilms and metal surfaces, MIC occurrences and mechanisms are difficult to predict and interpret. Many theories and mechanisms have been proposed to explain MIC. In this review, the mechanisms of MIC are discussed using bioenergetics, microbial respiration types, and biofilm extracellular electron transfer (EET). Two main MIC types, namely EET-MIC and metabolite MIC (M-MIC), are discussed. This brief review provides a state of the art insight into MIC mechanisms and it helps the diagnosis and prediction of occurrences of MIC under anaerobic conditions in the oil and gas industry.

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A transmission electron microscopy study of microscopic causes for localized-corrosion morphology variations in the AA7055 Al alloy
X.B. Yang, J.H. Chen, G.H. Zhang, L.P. Huang, T.W. Fan, Y. Ding, X.W. Yu
J. Mater. Sci. Technol.    2018, 34 (10): 1719-1729.   DOI: 10.1016/j.jmst.2018.05.006
Abstract   HTML PDF (6038KB)  

By Using (scanning) transmission electron microscopy, localized-corrosion morphology variations of the AA7055 AlZn(Cu)Mg alloy with different thermal processes and their underlying microscopic causes were investigated systematically. Our study shows that the corrosion resistance of the nanoscale precipitates varies with their structure type and Cu-content. Just like the Al-matrix, the early-stage precipitates are corrosion resistant, as compared with the ηp/η-precipitates without high Cu-content. With a high Cu-content, however, the η-precipitates become most corrosion resistant among all phases involved. Hence, tailoring the precipitate microstructure and chemistry though thermal processes may change the overall corrosion morphology and improve corrosion resistance property of the alloy.

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Constitutive equation and model validation for a 31 vol.% B4Cp/6061Al composite during hot compression
L. Zhou, C. Cui, Q.Z. Wang, C. Li, B.L. Xiao, Z.Y. Ma
J. Mater. Sci. Technol.    2018, 34 (10): 1730-1738.   DOI: 10.1016/j.jmst.2018.02.001
Abstract   HTML PDF (4268KB)  

An accurate constitutive equation is essential to understanding the flow behavior of B4C/Al composites during the hot deformation. However, the constitutive equations developed previously in literature are generally for low strain rate deformation. In the present work, we modified the general constitutive equation and take the high strain rate correction into account. The constitutive equation for a 31 vol.% B4Cp/6061Al composite was constructed based on the flow stresses measured during isothermal hot compression at temperatures ranging from 375 to 525 °C and strain rates from 0.01 to 10 s-1. The experimental flow stresses were corrected by considering temperature-dependent Arrhenius factor. The modified equation was then verified by using DEFORM-3D finite element analysis to simulate the experimental hot compression process. The results show that the modified equation successfully predicts flow stress, load-displacement, and the temperature rise. This helps to optimize the hot deformation process, and to obtain desirable properties, such as reduced porosity and homogenous particle distribution in B4C/Al composites.

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Microstructure and mechanical optimization of probeless friction stir spot welded joint of an Al-Li alloy
Q. Chu, W.Y. Li, X.W. Yang, J.J. Shen, A. Vairis, W.Y. Feng, W.B. Wang
J. Mater. Sci. Technol.    2018, 34 (10): 1739-1746.   DOI: 10.1016/j.jmst.2018.03.009
Abstract   HTML PDF (3541KB)  

In this work, a third generation Al-Li alloy has been successfully spot welded with probeless friction stir spot welding (P-FSSW), which is a variant of conventional friction stir welding. The Box-Behnken experimental design in response surface methodology (RSM) was applied to optimize the P-FSSW parameters to attain maximum tensile/shear strength of the spot joints. Results show that an optimal failure load of 7.83 kN was obtained under a dwell time of 7.2 s, rotation speed of 950 rpm and plunge rate of 30 mm/min. Sufficient dwell time is essential for heat conduction, material flow and expansion of the stir zone to form a sound joint. Two fracture modes were observed, which were significantly affected by hook defect. In addition to mechanical testing, electron backscattering diffraction (EBSD) and differential scanning calorimetry (DSC) were used for microstructure evolution and property analysis. The precipitation of GP zone and Al3Li as well as the ultrafine grains were responsible for the high microhardness in the stir zone.

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Dynamic recrystallization behavior and microstructural evolution of Mg alloy AZ31 through high-speed rolling
Jeong Hun Lee, Jong Un Lee, Sang-Hoon Kim, Seok Weon Song, Chong Soo Lee, Sung Hyuk Park
J. Mater. Sci. Technol.    2018, 34 (10): 1747-1755.   DOI: 10.1016/j.jmst.2018.03.002
Abstract   HTML PDF (7673KB)  

High-speed rolling (HSR) is known to improve the workability of Mg alloys significantly, which makes it possible to impose a large reduction in a single pass without fracture. In the present study, dynamic recrystallization (DRX) behavior and microstructural and textural variations of Mg alloy AZ31 during a HSR process were investigated by conducting rolling with different imposed reductions in the range of 20%-80% at a high rolling speed of 470 m/min and 400 °C. High-strain-rate deformation during HSR suppresses dislocation slips but promotes twinning, which results in the formation of numerous twins of several types, i.e., {10-12} extension twins, {10-11} and {10-13} contraction twins, and {10-11}-{10-12} double twins. After twinning, high strain energy is accumulated in twin bands because their crystallographic orientations are favorable for basal slips, leading to subsequent DRX at the twin bands. Accordingly, twinning activation and twinning-induced DRX behavior play crucial roles in accommodating plastic deformation during HSR and in varying microstructure and texture of the high-speed-rolled (HSRed) sheets. Area fraction of fine DRXed grains formed at the twin bands increases with increasing rolling reduction, which is attributed to the combined effects of increased strain, strain rate, and deformation temperature and a decreased critical strain for DRX. Size, internal strain, and texture intensity of the DRXed grains are smaller than those of unDRXed grains. Therefore, as rolling reduction increases, average grain size, stored internal energy, microstructural inhomogeneity, and basal texture intensity of the HSRed sheets gradually decrease owing to an increase in the area fraction of the DRXed grains.

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Effect of corrosion product films on the in vitro degradation behavior of Mg-3%Al-1%Zn (in wt%) alloy in Hank’s solution
B.J. Wang, D.K. Xu, J.H. Dong, W. Ke
J. Mater. Sci. Technol.    2018, 34 (10): 1756-1764.   DOI: 10.1016/j.jmst.2018.02.013
Abstract   HTML PDF (4520KB)  

Through investigating the corrosion behavior of an as-extruded Mg-3wt%Al-1wt%Zn (AZ31) alloy in a simulated physiological fluid of Hank’s solution, it demonstrates that the corrosion process was dependent on the immersion time. Further analyses revealed that the highest corrosion resistance could be obtained at 24 h due to the formation of a compact layer of corrosion products on the sample surface. With increasing the immersion time to up to 48 h, the thickness of surface films increased gradually but obvious de-bonding of such film from the substrate could take place, resulting in a certain resilience of the overall corrosion resistance.

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Quantitative analysis on friction stress of hot-extruded AZ31 magnesium alloy at room temperature
Ling Wang, Yiquan Zhao, Jing Zhang, Ru Ma, Yandong Liu, Yinong Wang, Qun Zhang, Weigang Li, Yuan Zhang
J. Mater. Sci. Technol.    2018, 34 (10): 1765-1772.   DOI: 10.1016/j.jmst.2018.02.011
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Mg alloy AZ31 with ~79% (volume fraction of scattering less than 30°) basal-fiber texture through hot extrusion exhibits strong grain-size dependent yield strength. Samples with grain sizes varying from 4.5 to 22.3 μm were obtained by altering annealing time durations. The Hall-Petch relations of tension and compression are σ0.2 = 86+200d-1/2 and σ0.2 = 17 + 327d-1/2, respectively. Considering the correlation between grain orientation and deformation modes, a novel weighted average method of calculating friction stress σ0 was proposed, and results of calculation agreed with the experimental ones, which can reasonably understand the yielding behavior in tension and compression.

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Basal-plane stacking-fault energies of Mg alloys: A first-principles study of metallic alloying effects
Qing Dong, Zhe Luo, Hong Zhu, Leyun Wang, Tao Ying, Zhaohui Jin, Dejiang Li, Wenjiang Ding, Xiaoqin Zeng
J. Mater. Sci. Technol.    2018, 34 (10): 1773-1780.   DOI: 10.1016/j.jmst.2018.02.009
Abstract   HTML PDF (1953KB)  

Generalized stacking-fault energies (GSFEs) of basal-plane stacking faults I1 and I2 in Mg alloys have been studied based on first-principles calculations, where 43 alloying elements were considered. It is found that the most contributing features of alloying elements to GSFEs are bulk modulus, equilibrium volume, binding energy, atomic radius and ionization energy. Both bulk modulus and ionization energy exhibit positive relationships with GSFEs, and the others show opposite relationships. Multiple regressions have been performed to offer a quantitative prediction for basal-plane GSFEs in Mg-X systems. GSFEs, alloying effects of elements and the prediction model established within this work may provide guidelines for new Mg alloys design with better ductility.

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Effect of nitrogen on corrosion behaviour of a novel high nitrogen medium-entropy alloy CrCoNiN manufactured by pressurized metallurgy
Hao Feng, Huabing Li, Xiaolei Wu, Zhouhua Jiang, Si Zhao, Tao Zhang, Dake Xu, Shucai Zhang, Hongchun Zhu, Binbin Zhang, Muxin Yang
J. Mater. Sci. Technol.    2018, 34 (10): 1781-1790.   DOI: 10.1016/j.jmst.2018.03.021
Abstract   HTML PDF (4104KB)  

A novel high nitrogen medium-entropy alloy CrCoNiN, which had higher strength and slightly lower ductility than CrCoNi alloy, was successfully manufactured by pressurized metallurgy. The microstructure and corrosion behaviour were investigated by microscopic, electrochemical and spectroscopic methods. The results indicated that nitrogen existed in the form of Cr2N precipitates and uniformly distributed N atoms, and nitrogen alloying significantly refined the grain size. Besides, nitrogen enriched on the outmost surface of passive film and metal/film interface as ammonia (NH3 and NH4+) and CrN, respectively. The significant improvement of corrosion resistance of CrCoNiN was attributed to the lower metastable pitting susceptibility together with thicker, less defective and more compact passive film.

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Experimental and numerical studies on the sluggish diffusion in face centered cubic Co-Cr-Cu-Fe-Ni high-entropy alloys
Rui Wang, Weimin Chen, Jing Zhong, Lijun Zhang
J. Mater. Sci. Technol.    2018, 34 (10): 1791-1798.   DOI: 10.1016/j.jmst.2018.02.003
Abstract   HTML PDF (3230KB)  

On purpose of studying the sluggish diffusion of high-entropy alloys, three different face centered cubic Co-Cr-Cu-Fe-Ni high-entropy alloys were prepared, and assembled into three groups of sandwich-type diffusion multiple annealed at 1273, 1323, and 1373 K respectively. By means of the electron probe microanalyzer technique and recently developed numerical inverse method, the composition-dependent interdiffusivities at different temperatures were effectively evaluated by minimizing the residual between the model-predicted compositions/interdiffusion fluxes and the respectively experimental ones. After that, the tracer diffusivities were predicted based on the assessed mobility parameters and thermodynamic descriptions with the simplified ideal solution model. The comprehensive comparison between the interdiffusivities/tracer diffusivities in the Co-Cr-Cu-Fe-Ni high-entropy alloys and those in sub-binary, ternary, quaternary and other quinary alloys indicates that the sluggish diffusion exists in interdiffusion instead of tracer diffusion for the present Co-Cr-Cu-Fe-Ni high-entropy alloys.

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Effect of scanning strategy on grain structure and crystallographic texture of Inconel 718 processed by selective laser melting
H.Y. Wan, Z.J. Zhou, C.P. Li, G.F. Chen, G.P. Zhang
J. Mater. Sci. Technol.    2018, 34 (10): 1799-1804.   DOI: 10.1016/j.jmst.2018.02.002
Abstract   HTML PDF (3765KB)  

Two types of scanning strategies were adopted to study the effect of scanning strategy on grain structure and crystallographic texture of selective laser melted (SLM) Inconel 718. The results show that bidirectional scanning without and with a 90°-rotation for every layer produced the bimodal grain structure and the directional columnar grain structure, respectively. Controlling the heat flux direction between the successive layers via scanning strategy enabled the formation of such different grain structures. Furthermore, when the 90°-rotation was applied, the competitive grain growth mechanism became more pronounced and the strong cube texture developed.

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Tensile, creep behavior and microstructure evolution of an as-cast Ni-based K417G polycrystalline superalloy
Beining Du, Ziyang Hu, Liyuan Sheng, Chuanyong Cui, Jinxia Yang, Yufeng Zheng, Xiaofeng Sun
J. Mater. Sci. Technol.    2018, 34 (10): 1805-1816.   DOI: 10.1016/j.jmst.2018.02.007
Abstract   HTML PDF (6203KB)  

The Ni-based K417G superalloy is extensively applied as aeroengine components for its low cost and good mid-temperature (600-900 °C) properties. Since used in as-cast state, the comprehensive understanding on its mechanical properties and microstructure evolution is necessary. In the present research, the tensile, creep behavior and microstructure evolution of the as-cast K417G superalloy under different conditions were investigated. The results exhibit that tensile cracks tend to initiate at MC carbide and γ/γ′ eutectic structure and then propagate along grain boundary. As the temperature for tensile tests increases from 21 °C to 700 °C, the yield strength and ultimate tensile strength of K417G superalloy decreases slightly, while the elongation to failure decreases greatly because of the intermediate temperature embrittlement. When the temperature rises to 900 °C, the yield strength and ultimate tensile strength would decrease significantly. The creep deformation mechanism varies under different testing conditions. At 760 °C/645 MPa, the creep cracks initiate at MC carbides and γ/γ′ eutectic structures, and propagate transgranularly. While at 900 °C/315 MPa and 950 °C/235 MPa, the creep cracks initiate at grain boundary and propagate intergranularly. As the creep condition changes from 760 °C/645 MPa to 900 °C/315 MPa and 950 °C/235 MPa, the γ′ phase starts to raft, which reduces the creep deformation resistance and increases the steady-state deformation rate.

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Improving friction stir weldability of Al/Mg alloys via ultrasonically diminishing pin adhesion
Xiangchen Meng, Yanye Jin, Shude Ji, Dejun Yan
J. Mater. Sci. Technol.    2018, 34 (10): 1817-1822.   DOI: 10.1016/j.jmst.2018.02.022
Abstract   HTML PDF (3245KB)  

Formation of intermetallic compounds (IMCs) during friction stir welding (FSW) of aluminum/magnesium (Al/Mg) alloys easily results in the pin adhesion and then deteriorates joint formation. The severe pin adhesion transformed the tapered-and-screwed pin into a tapered pin at a low welding speed of 30 mm/min. The pin adhesion problem was solved with the help of ultrasonic. The weldability of Al/Mg alloys was significantly improved due to the good material flow induced by mechanical vibration and the fragments of the IMCs on the surface of a rotating pin caused by acoustic streaming, respectively. A sound joint with ultrasonic contained long Al/Mg interface joining length and complex mixture of Al/Mg alloys in the stir zone, thereby achieving perfect metallurgical bonding and mechanical interlocking. The ultrasonic could broaden process window and then improve tensile properties. The tensile strength of the Al/Mg joint with ultrasonic reached 115 MPa.

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Microstructure and corrosion behavior of the heat affected zone of a stainless steel 308L-316L weld joint
Cheng Ma, Qunjia Peng, Jinna Mei, En-Hou Han, Wei Ke
J. Mater. Sci. Technol.    2018, 34 (10): 1823-1834.   DOI: 10.1016/j.jmst.2017.12.016
Abstract   HTML PDF (8212KB)  

Microstructure of the heat affected zone (HAZ) of a 308L-316L stainless steel (SS) weld joint and its corrosion behavior in high temperature water were studied. Peak of the residual strain was observed to approach to the fusion boundary in the HAZ while the strain increased from the top to root areas of the HAZ. The root area of the HAZ shows a lower corrosion resistance in high temperature water than the top and middle areas of the HAZ. This is attributed to a higher level of residual strain in association with a higher density of tangled dislocations in the top area of the HAZ. The results suggest that the residual strain in the HAZ could also promote the SCC through its effect on corrosion, in addition to that on the local microstructure and mechanical property of the steel.

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Friction and wear behaviors of a gradient nano-grained AISI 316L stainless steel under dry and oil-lubricated conditions
P.F. Wang, Z. Han
J. Mater. Sci. Technol.    2018, 34 (10): 1835-1842.   DOI: 10.1016/j.jmst.2018.01.013
Abstract   HTML PDF (3959KB)  

A gradient nano-grained (GNG) surface layer was fabricated on an AISI 316L stainless steel (SS) by using the surface mechanical rolling treatment (SMRT). Reciprocating dry and oil-lubricated sliding tests of the GNG 316L SS in air at room temperature were conducted in comparison with the coarse-grained (CG) counterpart. Worn surface morphologies and subsurface microstructures were investigated for both 316L SS samples. 316L SS with a GNG surface layer shows a significantly improved wear resistance, especially under oil-lubricated condition. The notably wear resistance enhancement of the GNG 316L SS is attributed to the GNG surface layer with high strain accommodation ability and high hardness, which can reduce the wear volume in the running-in stage effectively.

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Vacuum brazing of GH99 superalloy using graphene reinforced BNi-2 composite filler
Duo Liu, Yanyu Song, Bin Shi, Qi Zhang, Xiaoguo Song, Hongwei Niu, Jicai Feng
J. Mater. Sci. Technol.    2018, 34 (10): 1843-1850.   DOI: 10.1016/j.jmst.2018.02.008
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A novel graphene reinforced BNi-2 composite filler was developed for brazing GH99 superalloy. The interfacial microstructure of brazed joints was analyzed by field emission scanning electron microscope and a transmission electron microscope. The effects of graphene addition on the microstructure evolution and mechanical properties of brazed joints were investigated, and the strengthening mechanism of graphene was analyzed. The results revealed that due to the addition of graphene, M23(C,B)6 compounds were synthesized in the γ solid solution and brittle boride precipitates near the brazing seam decreased. Graphene was effective in retarding solute atoms diffusion thus impeding the precipitation of borides. Furthermore, the low coefficient of thermal expansion (CTE) of graphene was conducive to relieve stress concentration of the brazed joints during the cooling process. The shear strengths of brazed joints were significantly improved by exerting the strengthening effect of graphene. The maximum shear strengths of the brazed joints were 410.4 MPa and 329.7 MPa at room temperature and 800 °C, respectively.

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A comparison study of hydrogen storage properties of as-milled Sm5Mg41 alloy catalyzed by CoS2 and MoS2 nano-particles
Zeming Yuan, Bangwen Zhang, Yanghuan Zhang, Shihai Guo, Xiaoping Dong, Dongliang Zhao
J. Mater. Sci. Technol.    2018, 34 (10): 1851-1858.   DOI: 10.1016/j.jmst.2018.01.012
Abstract   HTML PDF (3455KB)  

The influences of the catalysts of CoS2 and MoS2 nano-particles on microstructure and hydrogen storage behaviors of as-milled Sm5Mg41 alloy have been compared in this work. The Sm5Mg41 + 5 wt.% M (M = CoS2, MoS2) alloys were prepared by milling the mechanical ground as-cast Sm5Mg41 alloy powders (particle size ≤ 75 μm) with 5 wt.% CoS2 or MoS2 nano-particles (particle size ≤ 30 nm), respectively. The results demonstrate that the CoS2 and MoS2 nanoparticles are embedded into the alloy surface, which is nanostructure containing some crystal defects, such as dislocation, grain boundary and twin etc. Those microstructures play a beneficial role in reducing the total potential barrier that the hydrogen absorption or desorption reactions must overcome, hence improving the hydrogen storage kinetics of the alloys. The as-milled alloys are composed of Sm5Mg41 and SmMg3 phases, and ball milling refines their crystal grains. The MgH2 and Sm3H7 phases appear after hydrogenation, while Mg and Sm3H7 phases exist after dehydrogenation. The dehydriding activation energy of M = CoS2 and MoS2 alloys are 101.67 and 68.25 kJ/mol H2 respectively. The initial hydrogen desorption of M = CoS2 and MoS2 alloys are 252.9 °C and 247.8 °C. The hydrogenation and dehydrogenation enthalpy changes of M = MoS2 alloy are a little smaller than that of M = CoS2 alloy. Therefore, the catalyst MoS2 can improve the as-milled Sm5Mg41 alloy in hydrogen storage property more effectively than CoS2.

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Mechanical properties of electron beam welded dissimilar joints of TC17 and Ti60 alloys
Chao Cheng, Bingbing Yu, Zhiyong Chen, Jianrong Liu,
J. Mater. Sci. Technol.    2018, 34 (10): 1859-1866.   DOI: 10.1016/j.jmst.2018.02.014
Abstract   HTML PDF (4143KB)  

Microstructure, hardness, tensile and high cycle fatigue (HCF) properties of the welded dissimilar joints of Ti60 and TC17 titanium alloys had been investigated in this study. A significant microstructural change was observed to occur after welding, with rod-like α and β phases in the fusion zone (FZ), equiaxed α phases, fine α laths and β phases in the heat-affected zone (HAZ) of TC17 side and acicular martensite α' phases+“ghost” α phases in the HAZ of Ti60 side. The microhardness across the joints exhibited an inhomogeneous distribution with the highest hardness of ~404 HV in FZ and the lowest hardness of ~304 HV in base material (BM) of Ti60. All the joints tested in tension fractured at BM of Ti60 side. Fatigue limits of the joints at 107 cycles were 425 MPa at room temperature and 380 MPa at 400 °C, respectively. Welding micropores were found to be the main source of fatigue crack initiation.

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Hot deformation behavior of Cu-bearing antibacterial titanium alloy
Zheng Ma, Ling Ren, M. Babar Shahzad, Rui Liu, Ying Zhao, Ke Yang
J. Mater. Sci. Technol.    2018, 34 (10): 1867-1875.   DOI: 10.1016/j.jmst.2017.12.015
Abstract   HTML PDF (6328KB)  

We investigated the deformation behavior of a new biomedical Cu-bearing titanium alloy (Ti-645 (Ti-6.06Al-3.75V-4.85Cu, in wt%)) to optimize its microstructure control and the hot-working process. The results showed that true stress-true strain curve of Ti-645 alloy was susceptible to both deformation temperature and strain rate. The microstructure of Ti-645 alloy was significantly changed from equiaxed grain to acicular one with the deformation temperature while a notable decrease in grain size was recorded as well. Dynamic recovery (DRV) and dynamic recrystallization (DRX) obviously existed during the thermal compression of Ti-645 alloy. The apparent activation energies in (α + β) phase and β single phase regions were calculated to be 495.21 kJ mol-1 and 195.69 kJ mol-1, respectively. The processing map showed that the alloy had a large hot-working region whereas the optimum window occurred in the strain rate range of 0.001-0.1 s-1, and temperature range of 900-960 °C and 1000-1050 °C. The obtained results could provide a technological basis for the design of hot working procedure of Ti-645 alloy to optimize the material design and widen the potential application of Ti-645 alloy in clinic.

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Electrochemical noise analysis on the pit corrosion susceptibility of biodegradable AZ31 magnesium alloy in four types of simulated body solutions
Changgang Wang, Liping Wu, Fang Xue, Rongyao Ma, Ini-Ibehe Nabuk Etim, Xuehui Hao, Junhua Dong, Wei Ke
J. Mater. Sci. Technol.    2018, 34 (10): 1876-1884.   DOI: 10.1016/j.jmst.2018.01.015
Abstract   HTML PDF (3625KB)  

Magnesium alloys have been investigated as biodegradable implant materials since the last century. Non-uniform degradation caused by local corrosion limits their application, and no appropriate technology has been used in the research. In this study, electrochemical noise has been used to study the pit corrosion on magnesium alloy AZ31 in four types of simulated body solutions, and the data have been analyzed using wavelet analysis and stochastic theory. Combining these with the conventional polarization curves, mass loss tests and scanning electron microscopy, the electrochemical noise results implied that AZ31 alloy in normal saline has the fastest corrosion rate, a high pit initiation rate, and maximum pit growth probability. In Hanks’ balanced salt solution and phosphate-buffered saline, AZ31 alloy has a high pit initiation rate and larger pit growth probability, while in simulated body fluid, AZ31 alloy has the slowest corrosion rate, lowest pit initiation rate and smallest pit growth probability.

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Electrodeposition and growth mechanism of preferentially orientated nanotwinned Cu on silicon wafer substrate
Fu-Long Sun, Li-Yin Gao, Zhi-Quan Liu, Hao Zhang, Tohru Sugahara, Shijo Nagao, Katsuaki Suganuma
J. Mater. Sci. Technol.    2018, 34 (10): 1885-1890.   DOI: 10.1016/j.jmst.2018.01.016
Abstract   HTML PDF (1903KB)  

Homogeneous columnar Cu film with fully embedded nanotwins was successfully fabricated on Ti/Cu seed layer on silicon wafer. The nanotwins with thickness of tens of nanometers are generally parallel to the silicon surface, showing a strong (111) preferred orientation. The acid concentration was found to be important in influencing the formation of nanoscale twins. By adjusting the acid concentration, the nanotwins can be induced from the top columnar grain to middle columnar grain and reach the bottom equiaxed grain, and a microstructural transformation model was given. A theory focusing on the cathode overpotential was proposed to reveal the effect of acid concentration on the growth mechanism of nanoscale twins. An appropriate adsorption proportion of hydrogen on cathode (acid concentration 17 ml L-1) could increase the overpotential which supplies adequate nucleation energy for nanoscale twins formation.

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Fabrication of novel ZnO/MnWO4 nanocomposites with p-n heterojunction: Visible-light-induced photocatalysts with substantially improved activity and durability
Mahsa Pirhashemi, Aziz Habibi-Yangjeh
J. Mater. Sci. Technol.    2018, 34 (10): 1891-1901.   DOI: 10.1016/j.jmst.2018.01.014
Abstract   HTML PDF (5513KB)  

We report, for the first time, binary ZnO/MnWO4 nanocomposites with p-n heterojunction fabricated by a simple ultrasonic-calcination route. The phase structure, morphology, and optical along with textural properties were comprehensively characterized. The photocatalytic performance was studied via degradations of rhodamine B, methyl blue and methyl orange (RhB, MB, MO), and fuchsine pollutants under visible-light illumination. The ZnO/MnWO4 nanocomposites exhibited better photocatalytic performance than their single components and the nanocomposite with 30 wt% MnWO4 showed the highest activity. Photocatalytic performance of this nanocomposite is 22.5, 17.7, 26.8, and 23.9 times higher than that of the ZnO sample in degradations of RhB, MB, MO, and fuchsine dyes, respectively. The improved photocatalytic performance was ascribed to the formation of p-n heterojunction between ZnO and MnWO4 with high charge separation efficiency as well as strong visible-light absorption ability. The possible mechanism for the improved photocatalytic performance was proposed. This study revealed that the novel ZnO/MnWO4p-n heterojunction can act as a promising visible-light-active photocatalyst for environmental applications.

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Silicon lithium-ion battery anode with enhanced performance: Multiple effects of silver nanoparticles
Shanshan Yin, Qing Ji, Xiuxia Zuo, Shuang Xie, Kai Fang, Yonggao Xia, Jinlong Li, Bao Qiu, Meimei Wang, Jianzhen Ban, Xiaoyan Wang, Yi Zhang, Ying Xiao, Luyao Zheng, Suzhe Liang, Zhaoping Liu, Cundong Wang, Ya-Jun Cheng
J. Mater. Sci. Technol.    2018, 34 (10): 1902-1911.   DOI: 10.1016/j.jmst.2018.02.004
Abstract   HTML PDF (4722KB)  

Silicon has been regarded as one of the most promising next generation lithium-ion battery anode. However, the poor cyclic stability of the Si based anode has severely limited its practical applications, which is even worse with high mass loading density (>1 mg cm-2). A new concept has been developed to enhance the electrochemical performance of the Si nanoparticle anode. Silver nanoparticles are composited with the silicon nanoparticles in a facile way for the first time. It is found that the mechanical properties of the Si electrode have been significantly improved by the incorporation of the silver nanoparticles, leading to enhanced cyclic performance. With the Si/Ag mass ratio of 4:1, the reversible specific discharge capacity is retained as 1156 mA h g-1 after 100 cycles at 200 mA g-1, which is more than three times higher than that of the bare silicon (318 mA h g-1). The rate performance has been effectively improved as well due to excellent electron conductivity of the silver nanoparticles.

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Core-shell structured MoS2@S spherical cathode with improved electrochemical performance for lithium-sulfur batteries
Songpu Cheng, Xiaohong Xia, Hongbo Liu, Yuxi Chen
J. Mater. Sci. Technol.    2018, 34 (10): 1912-1918.   DOI: 10.1016/j.jmst.2018.03.018
Abstract   HTML PDF (2850KB)  

To suppress shuttling effect and improve electrochemical performance of the sulfur cathode for lithium-sulfur batteries, core-shell structured MoS2@S spherical cathode has been synthesized through a chemical route using MnCO3 as template. The MoS2 shells consist of MoS2 nanosheets. For comparison, MoS2/S cathode has also been synthesized through melting and diffusion of sulfur to commercial MoS2 powders. The electrochemical performance of the MoS2@S and MoS2/S cathodes have been evaluated using cyclic voltammetry, discharge/charge cycling, electrochemical impedance spectroscopy coupled with impedance fitting. The electrochemical performance of the MoS2@S spherical cathode has been much improved compared with that of MoS2/S. The capacity of the MoS2@S spheres can reach 1185.7 mA h g-1 at 0.2 C and 955.1 mA h g-1 at 1 C with initial-cycle coulombic efficiency of 90%. The capacity fading of each cycle is 0.1% during 200 lithiation/delithiation cycles. The MoS2@S spherical cathode with high cyclic capacity and stability is promising cathode candidate for lithium-sulfur batteries.

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Direct growth of graphene on vertically standing glass by a metal-free chemical vapor deposition method
Zhongtao Chen, Xinli Guo, Long Zhu, Long Li, Yuanyuan Liu, Li Zhao, Weijie Zhang, Jian Chen, Yao Zhang, Yuhong Zhao
J. Mater. Sci. Technol.    2018, 34 (10): 1919-1924.   DOI: 10.1016/j.jmst.2018.02.005
Abstract   HTML PDF (2841KB)  

A new method to directly grow graphene on quartz glass substrate by atmospheric-pressure chemical vapor deposition (CVD) without using any catalyst was developed. The prime feature of this method is to build a vertical-glass model in the quartz tube to significantly increase the collision probability of the carbon precursors and reactive fragments between each other with the glass surface. The growth rate of high-quality graphene on glass remarkably increases compared with the conventional gas flow CVD technique. The optical transmittance and sheet resistance of the graphene glass can be readily adjusted by regulating growth time. When growth time is 35 min, the graphene glass presents an intriguing sheet resistance of about 1.48 kΩ sq-1 at a transmittance of 93.08% and exhibits an excellent hydrophobic performance. The method is simple and scalable, and might stimulate various potential applications of transparent and conductive graphene glass in practical fields.

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Tribological properties of copper matrix composites reinforced with homogeneously dispersed graphene nanosheets
Xin Gao, Hongyan Yue, Erjun Guo, Shaolin Zhang, Longhui Yao, Xuanyu Lin, Bao Wang, Enhao Guan
J. Mater. Sci. Technol.    2018, 34 (10): 1925-1931.   DOI: 10.1016/j.jmst.2018.02.010
Abstract   HTML PDF (4112KB)  

Graphene reinforced copper matrix composites (Gr/Cu) were fabricated by electrostatic self-assembly and powder metallurgy. The morphology and structure of graphene oxide, graphene oxide-Cu powders and Gr/Cu composites were characterized by scanning electronic microscopy, transmission electronic microscopy, X-ray diffraction and Raman spectroscopy, respectively. The effects of graphene contents, applied loads and sliding speeds on the tribological behavior of the composites were investigated. The results indicate that the coefficient of friction of the composites decreases first and then increases with increasing the graphene content. The lowest friction coefficient is achieved in 0.3 wt% Gr/Cu composite, which decreases by 65% compared to that of pure copper. The coefficient of friction of the composite does not have significant change with increasing the applied load, however, it increases with increasing the sliding speed. The tribological mechanisms of the composite under different conditions were also investigated.

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Synthesis of band gap-tunable alkali metal modified graphitic carbon nitride with outstanding photocatalytic H2O2 production ability via molten salt method
Xiaoyu Qu, Shaozheng Hu, Jin Bai, Ping Li, Guang Lu, Xiaoxue Kang
J. Mater. Sci. Technol.    2018, 34 (10): 1932-1938.   DOI: 10.1016/j.jmst.2018.04.019
Abstract   HTML PDF (2033KB)  

Band gap-tunable alkali metal modified graphitic carbon nitride was prepared by a molten salt method. X-ray diffraction, N2 isothermal sorption, ultraviolet-visible spectroscopy, scanning electron microscope, X-ray photoelectron spectroscopy and photoluminescence were used to characterize the obtained catalysts. The photocatalytic H2O2 production ability of as-prepared catalyst was investigated. The results indicate that K+ and Na+ are doped into g-C3N4 lattice simultaneously by the molten salt method. Alkali metal modification not only promotes the specific surface area, visible light absorption and separation of electron-hole pairs, but tunes the conduction band and valence band edge positions of as-prepared catalysts by controlling the weight ratio of eutectic salts to melamine. The tunable band edge positions result in the photocatalytic H2O2 production from “single channel pathway” to “two channel pathway”, leading to the promoted H2O2 production ability.

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Laminated Fe-34.5 Mn-0.04C composite with high strength and ductility
Yuhui Wang, Jianmei Kang, Yan Peng, Tiansheng Wang, Niels Hansen, Xiaoxu Huang
J. Mater. Sci. Technol.    2018, 34 (10): 1939-1943.   DOI: 10.1016/j.jmst.2018.05.013
Abstract   HTML PDF (2011KB)  

To obtain a good combination of strength and ductility, a laminated composite structure composed of recovered hard lamellae and soft recrystallized lamellae has been produced in a single phase austenitic Fe-34.5 Mn-0.04C steel by cold rolling and partial recrystallization. Enhanced mechanical properties in both strength and ductility have been obtained in the composite structure compared to a fully recrystallized coarse grain structure. A further increase in strength with only minor loss in total elongation has been achieved by a slight cold rolling of the composite structure, which also removes the small yield drop and Lüders elongation observed in the composite structure.

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Microstructure, biodegradation, antibacterial and mechanical properties of ZK60-Cu alloys prepared by selective laser melting technique
Cijun Shuai, Long Liu, Mingchun Zhao, Pei Feng, Youwen Yang, Wang Guo, Chengde Gao, Fulai Yuan
J. Mater. Sci. Technol.    2018, 34 (10): 1944-1952.   DOI: 10.1016/j.jmst.2018.02.006
Abstract   HTML PDF (3948KB)  

Magnesium (Mg) alloys are receiving increasing attention for body implants owing to their good biocompatibility and biodegradability. However, they often suffer from bacterial infections on account of their insufficient antibacterial ability. In this study, ZK60-xCu (x = 0, 0.2, 0.4, 0.6 and 0.8 wt%) alloys were prepared by selective laser melting (SLM) with alloying copper (Cu) to enhance their antibacterial ability. Results showed that ZK60-Cu alloys exhibited strong antibacterial ability due to combination of release of Cu ions and alkaline environment which could kill bacteria by destroying cellular membrane structure, denaturing enzymes and inhibiting deoxyribonucleic acid (DNA) replication. In addition, their compressive strength increased due to grain refinement and uniformly dispersing of short-bar shaped MgZnCu phases. Moreover, ZK60-Cu alloys also exhibited good cytocompatibility. In summary, ZK60-Cu alloys with antibacterial ability may be promising implants for biomedical applications.

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A first-principles investigation on mechanical and metallic properties of titanium carbides under pressure
Xiaojing Sha, Namin Xiao, Yongjun Guan, Xiaosu Yi
J. Mater. Sci. Technol.    2018, 34 (10): 1953-1958.   DOI: 10.1016/j.jmst.2018.02.012
Abstract   HTML PDF (1570KB)  

The titanium carbides are potential candidates to achieve both high hardness and refractory property. We carried out a structural search for titanium carbides at three pressures of 0 GPa, 30 GPa and 50 GPa. A phase diagram of the Ti-C system at 0 K was obtained by elucidating formation enthalpies as a function of compositions, and their mechanical and metallic properties of titanium carbides were investigated systematically. We also discussed the relation of titanium concentration to the both mechanical and metallic properties of titanium carbides. It has been found that the average valence electron density and tractility improved at higher concentrations of titanium, while the degree of covalent bonding directionality decreased. To this effect, the hardness of titanium carbide decreases as the content of titanium increases. Our results indicated that the titanium content significantly affected the metallic properties of the Ti-C system.

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