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      05 November 2019, Volume 35 Issue 11 Previous Issue    Next Issue
    Orginal Article
    Deformation and fracture mechanisms of an annealing-tailored “bimodal” grain-structured Mg alloy
    Baojie Wang, Daokui Xu, Liyuan Sheng, Enhou Han, Jie Sun
    J. Mater. Sci. Technol.. 2019, 35 (11): 2423-2429.   DOI: 10.1016/j.jmst.2019.06.008
    Abstract   HTML   PDF (4547KB)

    Through investigating and comparing the mechanical behavior of an as-rolled Mg-3%Al-1%Zn (wt%) alloy before and after annealing treatments, it was revealed that the formation of annealing-tailored bimodal grain structure ensured the 330 °C/4 h samples having a good combination of tensile strength and plasticity. Failure analysis demonstrated that for the as-rolled and 330 °C/1 h samples with fine grain structure, their plastic deformation was mainly attributed to basal slips, whereas the deformation mechanism in the bimodal grain-structured samples was dominated by basal slips in fine grains and twinning in coarse grains. For the 330 °C/8 h samples with coarse grain structure, high densities of twins were activated. Meanwhile, basal slips occurred in the twinned and un-twinned areas of coarse grains and could pass through twin boundaries. For differently treated samples, cracking preferentially occurred along slip bands, resulting in their transgranular fractures.

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    Additive manufacturing of high-strength CrMnFeCoNi high-entropy alloys-based composites with WC addition
    Jinfeng Li, Shuo Xiang, Hengwei Luan, Abdukadir Amar, Xue Liu, Siyuan Lu, Yangyang Zeng, Guomin Le, Xiaoying Wang, Fengsheng Qu, Chunli Jiang, Guannan Yang
    J. Mater. Sci. Technol.. 2019, 35 (11): 2430-2434.   DOI: 10.1016/j.jmst.2019.05.062
    Abstract   HTML   PDF (2482KB)

    Laser melting deposition with WC addition has been developed to fabricate high-strength CrMnFeCoNi-based high-entropy alloys-based composites. By this technique, a microstructure of compact refined equiaxed grains can be achieved, and the tensile strength can be remarkably improved. The sample with 5 wt% WC addition shows a promising mechanical performance with a tensile strength of 800 MPa and an elongation of 37%. The improvement in mechanical property may be attributed to the formation of Cr23C6 reinforcement precipitates, which could promote the heterogeneous nucleation of grains and hinder the propagation of slip bands.

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    Grain size effect on wear resistance of WC-Co cemented carbides under different tribological conditions
    Haibin Wang, Mark Gee, Qingfan Qiu, Hannah Zhang, Xuemei Liu, Hongbo Nie, Xiaoyan Song, Zuoren Nie
    J. Mater. Sci. Technol.. 2019, 35 (11): 2435-2446.   DOI: 10.1016/j.jmst.2019.07.016
    Abstract   HTML   PDF (8626KB)

    The grain-size dependence of wear resistance of WC-Co cemented carbides (with mean WC grain sizes of 2.2 μm, 1.6 μm, 0.8 μm and 0.4 μm, respectively) was investigated under different tribological conditions. The results showed that the grain size had opposite effects on wear resistance of the cemented carbides in dry sliding wear and microabrasion tests. In the former condition, with decrease of WC grain size hence the increase of hardness, plastic deformation, fracture, fragmentation and oxidation were all mitigated, leading to a drastic decrease in the wear rate. In the latter condition, pull-out of WC grains after Co removal dominated the wear, so that the hardness of cemented carbide was not a core factor. As a result, the wear resistance of the cemented carbide generally showed a decreasing trend with decrease of the grain size, except for a slight increase in the ultrafine-grained cemented carbide. Single-pass scratching of the cemented carbides under various loads indicated the same failure mechanism as that in the sliding wear tests. Furthermore, the reasons for severe surface oxidation of the coarse-grained cemented carbides were disclosed.

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    High-performance single-wall carbon nanotube transparent conductive films
    Song Jiang, Peng-Xiang Hou, Chang Liu, Hui-Ming Cheng
    J. Mater. Sci. Technol.. 2019, 35 (11): 2447-2462.   DOI: 10.1016/j.jmst.2019.07.011
    Abstract   HTML   PDF (6524KB)

    A single-wall carbon nanotube (SWCNT) has superior optical, electrical, and mechanical properties due to its unique structure and is therefore expected to be able to form flexible high-performance transparent conductive films (TCFs). However, the optoelectronic performance of these films needs to be improved to meet the requirements of many devices. The electrical resistivity of SWCNT TCFs is mainly determined by the intrinsic resistivity of individual SWCNTs and their junction resistance in networks. We analyze these key factors and focus on the optimization of SWCNTs and their networks, which include the diameter, length, crystallinity and electrical type of the SWCNTs, and the bundle size and interconnects in networks, as well as chemical doping and microgrid design. We conclude that isolated/small-bundle, heavily doped metallic or semiconducting SWCNTs with a large diameter, long length and high crystallinity are necessary to fabricate high-performance SWCNT TCFs. A simple, controllable way to construct macroscopic SWCNT networks with Y-type connections, welded junctions or microgrid design is important in achieving a low resistivity. Finally, some insights into the key challenges in the manufacture and use of SWCNT TCFs and their prospects are presented, hoping to shed light on promoting the practical application of SWCNT TCFs in future flexible and stretchable optoelectronics.

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    Negative permittivity derived from inductive characteristic in the percolating Cu/EP metacomposites
    Kai Sun, Jiahao Xin, Yaping Li, Zhongyang Wang, Qing Hou, Xiaofeng Li, Xinfeng Wu, Runhua Fan, Kwang Leong Choy
    J. Mater. Sci. Technol.. 2019, 35 (11): 2463-2469.   DOI: 10.1016/j.jmst.2019.07.015
    Abstract   HTML   PDF (1836KB)

    Recently, increasing attention has been concentrated on negative permittivity with the development of the emerging metamaterials composed of periodic array structures. However, taking facile preparation into consideration, it is important to achieve negative permittivity behavior based on materials’ intrinsic properties rather than their artificially periodic structures. In this paper, we proposed to fabricate the percolating composites with copper dispersed in epoxy (EP) resin by a polymerization method to realize the negative permittivity behavior. When Cu content in the composites reached to 80 wt%, the conductivity abruptly went up by three orders of magnitudes, suggesting a percolation behavior. Below the percolation threshold, the conductivity spectra conform to Jonscher’s power law; when the Cu/EP composites reached to percolating state, the conductivity gradually reduced in high frequency region due to the skin effect. It is indicated that the conductive mechanism changed from hopping conduction to electron conduction. In addition, the permittivity did not increase monotonously with the increase of Cu content in the vicinity of percolation threshold, due to the presence of leakage current. Meanwhile, the negative permittivity conforming to Drude model was observed above the percolation threshold. Further investigation revealed that there was a constitutive relationship between the permittivity and the reactance. When conductive fillers are slightly above the percolation threshold, the inductive characteristic derived from conductive percolating network leads to the negative permittivity. Such epsilon-negative materials can potentially be applied in novel electrical devices, such as high-power microwave filters, stacked capacitors, negative capacitance field effect transistors and coil-free resonators. In addition, the design strategy based on percolating composites provides an approach to epsilon-negative materials.

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    Residual stress distribution as a function of depth in graphite/copper brazing joints via X-ray diffraction
    Chun Li, Xiaoqing Si, Jian Cao, Junlei Qi, Zhibo Dong, Jicai Feng
    J. Mater. Sci. Technol.. 2019, 35 (11): 2470-2476.   DOI: 10.1016/j.jmst.2019.07.023
    Abstract   HTML   PDF (2003KB)

    The residual stress distributions as a function of depth in three different graphite/copper brazing joints: with no interlayer, with a copper interlayer and with a niobium interlayer are measured via X-ray diffraction by transmission geometry. The residual stress in all the joints is found to be generally compressive and increasing from the surface to the interface. Copper and niobium interlayers are both effective in alleviating the residual stress in the joint and the stress value in the joint with a niobium interlayer appearing to be the lowest. The strength of the joint is demonstrated to be closely related to the residual stress and the fracture position of the joint corresponds well with the highest residual stress.

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    Effects of icosahedral phase on mechanical anisotropy of as-extruded Mg-14Li (in wt%) based alloys
    Chuanqiang Li, Daokui Xu, Baojie Wang, Liyuan Sheng, Ruizhi Wu, Enhou Han
    J. Mater. Sci. Technol.. 2019, 35 (11): 2477-2484.   DOI: 10.1016/j.jmst.2019.07.028
    Abstract   HTML   PDF (3050KB)

    Through investigating and comparing microstructure and crystallographic texture of as-extruded Mg-14Li and Mg-14Li-6Zn-1Y (in wt%) alloys, the differences in their mechanical anisotropy were investigated. It revealed that the formation of I-phase (Mg3Zn6Y, icosahedral structure) can effectively refine grain size. Moreover, compared with Mg-14Li alloy, the texture type of Mg-14Li-6Zn-1Y alloy changed slightly, but its texture intensity decreased remarkably. As a result, the stronger texture contributed to the “normal” mechanical anisotropy of Mg-14Li alloy with higher tensile strength and a lower elongation ratio along transverse direction (TD) than those along extrusion direction (ED). However, for Mg-14Li-6Zn-1Y alloy, the zonal distribution of I-phase particles along ED caused “abnormal” mechanical anisotropy, i.e. higher tensile strength and better plasticity along ED.

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    Wüstite-type Fe0.78Mn0.22O nanocubes: A new class for high-sensitive T2-weighted magnetic resonance imaging agent
    Huawei Rong, Haihua Hu, Jian Zhang, Jianjun Wang, Mu Zhang, Gaowu Qin, Yanhui Zhang, Xuefeng Zhang
    J. Mater. Sci. Technol.. 2019, 35 (11): 2485-2493.   DOI: 10.1016/j.jmst.2019.07.030
    Abstract   HTML   PDF (3185KB)

    Wüstite-type Fe0.78Mn0.22O nanocubes, with a uniform size of ~10 nm in edge length, have been synthesized by thermal-decomposition approach. The nanocubes exhibited superparamagnetic properties at room temperature, associated with a magnetization of 12.6 emu/g. These Fe0.78Mn0.22O nanocubes present transversal (r2) and longitudinal (r1) relaxivities of 325.9 and 0.518 mM-1 s-1 at 7 T for water protons. The ratio of the r2/r1 (629.2) ranks them being the highest sensitivity (r2/r1) comparable to currently reported T2-weighted magnetic resonance imaging (MRI) agents. Meanwhile, the Fe0.78Mn0.22O nanocubes were functionalized and demonstrated to be biocompatible when attached to the surface of mesenchymal stem cells, therefore showing the promise as a new class of MRI agents in clinic applications.

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    Biofilm inhibition and corrosion resistance of 2205-Cu duplex stainless steel against acid producing bacterium Acetobacter aceti
    Dan Liu, Ru Jia, Dake Xu, Hongying Yang, Ying Zhao, M. saleem Khan, Songtao Huang, Jiankang Wen, Ke Yang, Tingyue Gu
    J. Mater. Sci. Technol.. 2019, 35 (11): 2494-2502.   DOI: 10.1016/j.jmst.2019.05.048
    Abstract   HTML   PDF (4403KB)

    Acid producing bacterium Acetobacter aceti causes pitting corrosion of stainless steel (SS). This work investigated the enhanced resistance of 2205-Cu duplex stainless steel (DSS) against biocorrosion by A. aceti in comparison with 2205 DSS using electrochemical and surface analysis techniques. With the addition of Cu to 2205 DSS, biofilms on the 2205-Cu DSS surface were inhibited effectively. The largest pit depth on 2205-Cu DSS surface in the presence of A. aceti was 2.6 μm, smaller than 5.5 μm for 2205 DSS surface. The icorr was 0.42 ± 0.03 μA cm-2 for 2205-Cu DSS in the biotic medium, which was much lower than that for 2205 DSS (3.69 ± 0.65 μA cm-2). All the results indicated that the A. aceti biofilm was considerably inhibited by the release of Cu2+ ions from the 2205-Cu DSS matrix, resulting in the mitigation of biocorrosion by A. aceti.

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    In vitro investigation of cellular effects of magnesium and magnesium-calcium alloy corrosion products on skeletal muscle regeneration
    Diana Maradze, Andrew Capel, Neil Martin, Mark P.Lewis, Yufeng Zheng, Yang Liu
    J. Mater. Sci. Technol.. 2019, 35 (11): 2503-2512.   DOI: 10.1016/j.jmst.2019.01.020
    Abstract   HTML   PDF (4106KB)

    Biodegradable magnesium (Mg) has garnered attention for its use in orthopaedic implants due to mechanical properties that closely match to those of bone. Studies have been undertaken to understand the corrosion behaviour of these materials and their effects on bone forming cells. However, there is lack of research on how the corrosion of these biomaterials affect surrounding tissues such as skeletal muscle. Mg plays an important role in the structural and functional properties of skeletal muscle. It is therefore important to investigate the response of skeletal muscle cells to both soluble (Mg ions) and insoluble (corrosion granules) corrosion products. Through in vitro studies it is possible to observe the effects of corrosion products on myotube formation by the fusion of single muscle precursor cells known as myoblasts. To achieve this goal, it is important to determine if these corrosion products are toxic to myotubes. Here it was noted that although there was a slight decrement in cellular viability after initial exposure, this soon recovered to control levels. A high Ca/Mg ratio resulted in the formation of large myotubes and a low Ca/Mg ratio negatively affected myotube maturation. Mg2+ and Ca2+ ions are important in the process of myogenesis, and the concentration of these ions and the ratio of the ions to each other played a significant role in myotube cellular activity. The outcomes of this study could pave the way to a bio-informed and integrated approach to the design and engineering of Mg-based orthopaedic implants.

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    Characterization of the prior particle boundaries in a powder metallurgy Ti2AlNb alloy
    Jinhu Zhang, Jinmin Liu, Dongsheng Xu, Jie Wu, Lei Xu, Rui Yang
    J. Mater. Sci. Technol.. 2019, 35 (11): 2513-2525.   DOI: 10.1016/j.jmst.2019.04.036
    Abstract   HTML   PDF (8337KB)

    Ti2AlNb-based alloy powder metallurgy (PM) compacts were prepared via hot isostatic pressing (HIP) under relatively low temperature (920 and 980 °C) and at certain pressure (130 MPa). The microstructure, composition and orientation of B2, α2 and O phases in the compacts were characterized and analyzed with an aim to investigate the effect of unsuitable HIPping parameters on the appearance of prior particle boundary (PPB), which seriously affects the mechanical properties of the alloy. The results show that more α2 phase is the characteristics of the PPB in Ti2AlNb-based alloy when HIPped at relatively low temperature. Increasing HIPping temperature to the upper part of the two-phase region can effectively inhibit the formation of PPB. Electron backscatter diffraction measurements show the specific orientation relationship between phases, which helps us understand the origin of α2 and O phase and the corresponding transformation path. The HIPping at a higher temperature can weaken the micro-texture intensity of the α2 and O phase due to the increase of misorientation in B2 phase. The α2 phase at cell wall keeps the Burgers orientation relationship (BOR) with the grain on one side, and does not satisfy the BOR with the other. It is found that some O phase variants inside the cell HIPped at 980 °C can only maintain α2-O OR with α2 owing to the α2→O phase transformation forming the O phase, while these O variants deviate from B2-O OR with B2 phase.

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    Effect of vanadium micro-alloying on the microstructure evolution and mechanical properties of 718H pre-hardened mold steel
    Liu Hanghang, Fu Paixian, Liu Hongwei, Sun Chen, Du Ningyu, Li Dianzhong
    J. Mater. Sci. Technol.. 2019, 35 (11): 2526-2536.   DOI: 10.1016/j.jmst.2019.04.033
    Abstract   HTML   PDF (6341KB)

    The effects of different contents of vanadium (V) (0.1, 0.2, and 0.3 wt%) on the microstructure evolution and mechanical properties of 718H steel were investigated. The precipitate was characterized by means of atom probe tomography (APT) and bright-field transmission electron microscopy (TEM). The increase in V content has great benefits for strength, but has an adverse effect on impact toughness. The strength increase can be attributed to the influence of V addition on dislocation density, misorientation gradient, and fine scale MC precipitates. Precipitation strengthening mainly contributes to the V-added steel by analyzing various strengthening mechanisms. However, fine scale MC precipitates can pin dislocation leading to a decrease in its mobility. A large number of immovable dislocations will increase the dislocation accumulation, internal stress and brittle cracking, resulting in a gradual decrease in impact toughness with the V addition. In addition, compared with V-free steel, the dissolved V content in austenite decreases the grain boundary energy and inhibits the diffusion of the C atoms, ultimately reducing the transformation range of pearlite (P).

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    Effects of Al on microstructural stability and related stress-rupture properties of a third-generation single crystal superalloy
    Sun Jingxia, Liu Jinlai, Liu Lirong, Zhou Yizhou, Li Jinguo, Sun Xiaofeng
    J. Mater. Sci. Technol.. 2019, 35 (11): 2537-2542.   DOI: 10.1016/j.jmst.2019.05.003
    Abstract   HTML   PDF (2293KB)

    To examine the influences of minor modification of Al content on the microstructural stabilities and stress rupture properties, two alloys with minor difference in Al content were exposed isothermally at 1100 °C for 100 h, 500 h, and 1000 h, respectively. The microstructures were characterized before and after thermal exposure. It was found that when Al content was decreased by 0.4 wt %, the volume fraction γ′ decreased by 4 %, the size of γ′ increased by 40 nm, the matrix channel width increased by 5 nm, and the misfit degree of γ/γ′ phases increased by 0.006 % after heat treatment (HT). During thermal exposure, the alloy with low Al content had a better resistance to coarsening of γ′ phase and precipitation of μ phase. The γ′ particles of the alloy with high Al content tended to connect each other and coarsened along <100>directions; however, the γ′ particles of the alloy with low Al content remained cubic after 500 h. A serious coarsening behavior took place in the two alloys after aging for 1000 h. The structural stabilities were significantly improved. However, the change of 0.4 wt % Al content was found to have little effect on the high temperature stress-rupture properties.

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    Nitrogen-doped graphite encapsulated Fe/Fe3C nanoparticles and carbon black for enhanced performance towards oxygen reduction
    Zhu Jie, Xiong Zewei, Zheng Jiming, Luo Zhihong, Zhu Guangbin, Xiao Chao, Meng Zhengbing, Li Yibing, KunLuo
    J. Mater. Sci. Technol.. 2019, 35 (11): 2543-2551.   DOI: 10.1016/j.jmst.2019.07.008
    Abstract   HTML   PDF (3279KB)

    Non-noble metal (NNM) catalysts have recently attracted intensive interest for their high catalytic performance towards oxygen reduction reaction (ORR) at low cost. Herein, a novel NNM catalyst was synthesized by the simple pyrolysis of carbon black, urea and a Fe-containing precursor, which exhibits excellent ORR catalytic activity, superior durability and methanol tolerance versus the Pt/C catalyst in both alkaline and acidic solutions. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) characterizations demonstrate that the product is a nitrogen-doped hybrid of graphite encapsulated Fe/Fe3C nanoparticles and carbon black. X-ray photoelectron spectrum (XPS) and electrochemical analyses indicate that the catalytic performance and chemical stability correlate closely with a nitrogen-rich layer on the Fe/Fe3C nanoparticle after pyrolysis with presence of urea, leading to the same four-electron pathway towards ORR as the Pt/C catalyst. The hybrid is prospective to be an efficient ORR electrocatalyst for direct methanol fuel cells with high catalytic performance at low cost.

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    Deformation behaviors of as-built and hot isostatically pressed Ti-6Al-4V alloys fabricated via electron beam rapid manufacturing
    Liu Z., Zhao Z.B., Liu J.R., Wang L., Zhu S.X., Yang G., Gong S.L., Wang Q.J., ang R.Y
    J. Mater. Sci. Technol.. 2019, 35 (11): 2552-2558.   DOI: 10.1016/j.jmst.2019.04.032
    Abstract   HTML   PDF (3278KB)

    The deformation behavior of as-built and hot isostatically pressed (HIP) Ti-6Al-4 V alloys fabricated using electron beam rapid manufacturing (EBRM) were investigated in this work. The deformation characteristics were characterized using a laser scanning confocal microscope and electron back-scattered diffraction (EBSD). In the as-built sample, prismatic slip was the main mode of deformation, as well as a small amount of basal slip and cross-slip. Some planar slip lines with large length scales were observed across several α lamellae. After hot isostatical pressing, prismatic and basal slip were the main mode of deformation, accompanied by abundant cross-slip and multiple slip, and most of the slip lines were blocked within an α lamellae. These differences in deformation behavior were associated with the coarsening of α laths and the more retained β phase after HIP compared to the as-built alloy. More cross-slip and multiple slip can lead to superior elongation-to-failure and a greater strain hardening effect in the HIP alloy compared to the as-built sample.

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    Self-lubricating bidirectional carbon fiber reinforced smart aluminum composites by squeeze infiltration process
    Sree Manu K.M., Ajay Raag L., Rajan T.P.D., Pai B.C., Petley Vijay, Namdeo Verma Shweta
    J. Mater. Sci. Technol.. 2019, 35 (11): 2559-2569.   DOI: 10.1016/j.jmst.2019.04.034
    Abstract   HTML   PDF (7116KB)

    Self-lubrication is one of the smart material properties required for producing components with enhanced wear resistance and low coefficient of friction. Bidirectional (BD) satin weave polyacrylonitrile (PAN) based carbon fiber (Cf) fabric preform was successfully infiltrated with Al 6061 alloy by squeeze infiltration process. The infiltrated composite shows uniform distribution of carbon fibers in the matrix with the elimination of porosities, fiber damage and close control on the formation of deleterious aluminum carbide (Al4C3) phase. Cf/Al composite exhibits remarkable wear resistance compared to unreinforced alloy due to the formation of self-lubricating tribolayer on the pin surface, which intercepts the contact of matrix metal to counter surface. The BD carbon fiber enhanced the hardness and compressive strength of the composite by restraining the plastic flow behavior of matrix. High resolution transmission electron microscopy shows the presence of Al2O3 and MgAl2O4 spinel, confirmed by EDS and SAD pattern, at the composite interface. The composite shows a lower density of 2.16 g/cm3 which is a major advantage for weight reduction compared to the monolithic alloy (2.7 g/cm3).

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    Relationship of particle stimulated nucleation, recrystallization and mechanical properties responding to Fe and Si contents in hot-extruded 7055 aluminum alloys
    She Huan, Shu Da, Dong Anping, Wang Jun, Sun Baode, Lai Hongchang
    J. Mater. Sci. Technol.. 2019, 35 (11): 2570-2581.   DOI: 10.1016/j.jmst.2019.07.014
    Abstract   HTML   PDF (6412KB)

    The variations of coarse intermetallic particles in hot-extruded 7055 aluminum alloys with 0.041 wt% Fe and 0.024 wt% Si increasing to 0.272 wt% Fe and 0.134 wt% Si were investigated. The particle stimulated nucleation (PSN) behaviors for different kind of coarse particles were detailly analyzed by EBSD. Moreover, the effect of PSN responding to Fe and Si contents on recrystallization and tensile properties of 7055 alloys was evaluated. With increasing Fe and Si contents, the size and number density of coarse η/S particles are reduced, while the number densities of coarse Al7Cu2Fe and Mg2Si particles are both increased and the coarse Al7Cu2Fe particles transform from rod-like to irregular. More PSN recrystallized grains with predominant orientations deviated from the extruded fiber textures are stimulated by the irregular Al7Cu2Fe and Mg2Si particles, because a higher degree of local non-uniform deformation is produced. The rod-like Al7Cu2Fe particles cause the greatest degree of local non-uniform deformation owing to the largest aspect ratio, but the shape also restricts the area of particle deformation zone (PDZ) resulting in fewer PSN recrystallized grains. The irregular η/S particles give rise to the lowest degree of local non-uniform deformation and fewest PSN recrystallized grains with the major orientations close to the extruded fiber textures. Consequently, despite the number and size of coarse η/S particles are reduced, the proportion of high angle grain boundaries (HAGBs) is increased and the extruded fiber textures are weakened with Fe and Si contents increasing, because of the increased Al7Cu2Fe and Mg2Si particles. The strength is slightly declined by the weakened <111>//ED (extrusion direction) fiber texture, while the elongation is reduced for a larger number of coarse particles and more HAGBs with higher Fe and Si contents.

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    Mechanism for the multi-stage precipitation of Fe-Ni based alloy
    Jiang Yan, Zuo Qiang, Liu Feng
    J. Mater. Sci. Technol.. 2019, 35 (11): 2582-2590.   DOI: 10.1016/j.jmst.2019.05.064
    Abstract   HTML   PDF (3188KB)

    This work lays great emphasis on the distribution evolution of sigma (σ) phase in Fe-Ni based N08028 alloy during aging process, the result of which could provide new insights into phase change and precipitation mechanism. It is found that the σ phase, in any case, tends to separate out with a granular shape at grain boundaries (GBs) primarily, and with the increment of time, it is obliged to precipitate in grain interiors (GIs) with a lamellar structure. The mechanisms for the evolving volume fraction and morphology of σ phase are discussed, and a model appropriate for the multi-stage behavior transforming from intergranular to intragranular precipitation is derived, as well as revealing the thermodynamics and transformation kinetics corresponding to this process. The results reveal that the occurrence of multi-stage precipitation is correlated with the redistribution of solute atoms and with the difference in coupling effect of thermodynamic driving force and kinetic activation energy between the intergranular and intragranular precipitation.

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    Superplastic behavior of a powder metallurgy superalloy during isothermal compression
    Tan Liming, Li Yunping, Liu Feng, Nie Yan, Jiang Liang
    J. Mater. Sci. Technol.. 2019, 35 (11): 2591-2599.   DOI: 10.1016/j.jmst.2019.05.025
    Abstract   HTML   PDF (5638KB)

    In this work, the flow behaviors and microstructure evolution of a powder metallurgy nickel-based superalloy during superplastic compression is investigated. Based on the strain rate sensitivity m determined by flow data, superplastic region is estimated at relatively low temperature and strain rate domains, specifically around 1000 °C/10-3 s-1. Thereafter, the cylinder specimens are isothermally compressed at 1000 °C/10-3 s-1 and 1025 °C/10-3 s-1 with different strains, to exam the superplasticity and related mechanisms. The experimental results indicate that the accumulated dislocations are mainly annihilated by dynamic recovery and dynamic recrystallization (DRX), and the grain boundary sliding (GBS) contributes to the total strain during superplastic compression as well. In addition, the cavities and cracks at triple junctions or interfaces between matrix and second phase particle have not been detected, which is different from superplastic tensile deformation.

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    Microstructure and mechanical properties of ultra-fine grained MoNbTaTiV refractory high-entropy alloy fabricated by spark plasma sintering
    Liu Qing, Wang Guofeng, Sui Xiaochong, Liu Yongkang, Li Xiao, Yang Jianlei
    J. Mater. Sci. Technol.. 2019, 35 (11): 2600-2607.   DOI: 10.1016/j.jmst.2019.07.013
    Abstract   HTML   PDF (3379KB)

    The MoNbTaTiV refractory high-entropy alloy (RHEA) with ultra-fine grains and homogeneous microstructure was successfully fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). The microstructural evolutions, mechanical properties and strengthening mechanisms of the alloys were systematically investigated. The nanocrystalline mechanically alloyed powders with simple body-centered cubic (BCC) phase were obtained after 40 h MA process. Afterward, the powders were sintered using SPS in the temperature range from 1500 °C to 1700 °C. The bulk alloys were consisted of submicron scale BCC matrix and face-centered cubic (FCC) precipitation phases. The bulk alloy sintered at 1600 °C had an average grain size of 0.58 μm and an FCC precipitation phase of 0.18 μm, exhibiting outstanding micro-hardness of 542 HV, compressive yield strength of 2208 MPa, fracture strength of 3238 MPa and acceptable plastic strain of 24.9% at room temperature. The enhanced mechanical properties of the MoNbTaTiV RHEA fabricated by MA and SPS were mainly attributed to the grain boundary strengthening and the interstitial solid solution strengthening. It is expectable that the MA and SPS processes are the promising methods to synthesize ultra-fine grains and homogenous microstructural RHEA with excellent mechanical properties.

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    Nano-SiC reinforced Zn biocomposites prepared via laser melting: Microstructure, mechanical properties and biodegradability
    Gao Chengde, Yao Meng, Shuai Cijun, Peng Shuping, Deng Youwen
    J. Mater. Sci. Technol.. 2019, 35 (11): 2608-2617.   DOI: 10.1016/j.jmst.2019.06.010
    Abstract   HTML   PDF (5079KB)

    Zn has been regarded as new kind of potential implant biomaterials due to the desirable biodegradability and good biocompatibility, but the low strength and ductility limit its application in bone repairs. In the present study, nano-SiC was incorporated into Zn matrix via laser melting, aiming to improve the mechanical performance. The microstructure analysis showed that nano-SiC distributed along Zn grain boundaries. During the laser rapid solidification, nano-SiC particles acted as the sites for heterogeneous nucleation, which resulted in the reduction of Zn grain size from 250 μm to 15 μm with 2 wt% SiC (Zn-2SiC). Meanwhile, nano-SiC acted as a reinforcer by virtue of Orowan strengthening and dispersion strengthening. As a consequence, the nanocomposites showed maximal compressive yield strength (121.8 ± 5.3 MPa) and high microhardness (72.24 ± 3.01 HV), which were increased by 441% and 78%, respectively, compared with pure Zn. Moreover, fracture analysis indicated a more ductile fracture of the nanocomposites after the incorporation of nano-SiC. In addition, the nanocomposites presented favorable biocompatibility and accelerated degradation caused by intergranular corrosion. These findings suggested that the nano-SiC reinforced Zn biocomposites may be the potential candidates for orthopedic implants.

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    High-performance hot-warm rolled Zn-0.8Li alloy with nano-sized metastable precipitates and sub-micron grains for biodegradable stents
    Li Zhen, Shi Zhang-Zhi, Hao Yuan, Li Hua-Fang, Liu Xue-Feng, Volinsky Alex A., Zhang Hai-Jun, Wang Lu-Ning
    J. Mater. Sci. Technol.. 2019, 35 (11): 2618-2624.   DOI: 10.1016/j.jmst.2019.06.009
    Abstract   HTML   PDF (3553KB)

    Fabricated through a newly developed hot-warm rolling process, Zn-0.8Li (wt%) alloy has ideal strength and ductility far beyond the mechanical benchmark of materials for biodegradable stents. Precipitation of needle-like Zn in primary β-LiZn4 phase is observed in Zn-Li alloy for the first time. Orientation relationship between them can be described as [1-213]β//[2-1-10]Zn, (10-10)β about 4.5° from (0002)Zn. Zn grains with an average size of 640 nm exhibit strong basal texture, detected by transmission electron back-scatter diffraction. Li distribution is determined by three-dimensional atom probe, which reveals the formation of nano-sized metastable α-Li2Zn3 precipitates with a number density of 7.16 × 1022 m-3. The fine lamellar Zn + β-LiZn4 structure, sub-micron grains and the nano-sized precipitates contribute to the superior mechanical properties.

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    The stability of deformation twins in aluminum enhanced by alloying elements
    Liu Linghong, Chen Jianghua, Fan Touwen, Shang Shunli, Shao Qinqin, Yuan Dingwang, Dai Yu
    J. Mater. Sci. Technol.. 2019, 35 (11): 2625-2629.   DOI: 10.1016/j.jmst.2019.07.029
    Abstract   HTML   PDF (1448KB)

    Introducing and stabilizing twins in aluminum is a challenge for metals research due to their high formation energy. Employing first-principles calculations, we investigated the twin boundary segregation of alloying elements and their impact on the twin boundary energy in aluminum. Alloying elements with small solubilities but strong interaction with twin boundary would significantly reduce twin boundary energies in aluminum at low temperatures. With increasing temperature, their segregation near twin boundary weakens, leading to their influence on twin boundary energies reduced. Some elements with large solubilities may greatly reduce the twin energies not only at low temperatures but also at high temperatures. Based on careful analysis of charge density and atomic radius, it has been found that chemical difference has little influence on twin boundary energy whereas the atomic size effect plays a leading role in causing the change of twin boundary energy.

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    Enhancing the mechanical and anticorrosion properties of 316L stainless steel via a cathodic plasma electrolytic nitriding treatment with added PEG
    Zhang Tianyi, Wu Junsheng, Jin Lei, Zhang Zhan, Rong Wan, Zhang Bowei, Wang Yi, He Yedong, Liu Wei, Li Xiaogang
    J. Mater. Sci. Technol.. 2019, 35 (11): 2630-2637.   DOI: 10.1016/j.jmst.2019.07.031
    Abstract   HTML   PDF (2850KB)

    A cathodic plasma electrolytic nitriding (CPEN) treatment with a urea aqueous solution was performed on 316L stainless steel to rapidly improve its surface properties in this work. Test results show that the PEG2000 macromolecules increased the nitriding energy via enhancing the ability to bond the produced gas film to the metal/electrolyte interface. The cross-sectional morphologies indicate that a thick nitrided layer was obtained when the urea concentration was 543 g l-1, corresponding to a Vickers hardness 450 HV0.1, which was 3.5 times larger than that of the substrate. The nitrided layer mainly contained expanded austenite (γN), oxides and iron nitrides (e.g., Fe3O4 and FeN0.076). In terms of its performance, coefficient of friction (COF) of the nitride layer decreased to nearly two-thirds that of the untreated layer, and the passivation current densities of the nitrided sample in a 3.5% NaCl solution decreased by an order of magnitude compared to that of the substrate. Therefore, the approach presented herein provides an attractive way to modify the effect of CPEN in a urea aqueous solution.

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    A molecular dynamics study on formation of the self-accommodation microstructure during phase transformation
    Sun Zhi-peng, Zhang Jin-yu, Dai Fu-zhi, Xu Ben, Zhang Wen-zheng
    J. Mater. Sci. Technol.. 2019, 35 (11): 2638-2646.   DOI: 10.1016/j.jmst.2019.04.035
    Abstract   HTML   PDF (2426KB)

    Self-accommodation microstructure, a typical crystallographic texture developed from phase transformation, is often observed in various alloys. In this work, a molecular dynamics simulation was conducted to reveal the fine details of self-accommodation microstructure evolution during the phase transformation from austenite to ferrite in pure iron. The growth and shrinkage of ferrite grains with different orientation relationships (ORs) are interpreted based on the analysis combining the elastic interaction energy and the interfacial energy. It was found that the strain energy determines the priority of potential ORs, while the interfacial energy selects the specific preferred ORs to form. The present atomistic process and energetic interpretation of the self-accommodation microstructure provide helpful insight into phase transformation textures observed in various alloys.

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    (La0.2Ce0.2Nd0.2Sm0.2Eu0.2)2Zr2O7: A novel high-entropy ceramic with low thermal conductivity and sluggish grain growth rate
    Zhao Zifan, Xiang Huimin, Dai Fu-Zhi, Peng Zhijian, Zhou Yanchun
    J. Mater. Sci. Technol.. 2019, 35 (11): 2647-2651.   DOI: 10.1016/j.jmst.2019.05.054
    Abstract   HTML   PDF (2606KB)
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    Solidification pathway and phase transformation behavior in a beta-solidified gamma-TiAl based alloy
    Xu H., Li X.B., Xing W.W., Shu L., Ma Y.C., Liu K.
    J. Mater. Sci. Technol.. 2019, 35 (11): 2652-2657.   DOI: 10.1016/j.jmst.2019.05.061
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    The phase transformation behavior of an as-cast Ti-42Al-5 Mn (at.%) alloy after subsequent quenching from 1380 °C to 1000 °C was investigated based on the differential thermal analysis (DTA), electron probe micro analyzer-backscattered electrons (EPMA-BSE), transmission electron microscope (TEM) and X-ray diffraction (XRD). The results show that, the solidification path can be summarized as follows: Liquid→Liquid+β→β→β + α→β + α+γ→βo2+γ→βo+γ+α2/γ→βo+γ+α2/γ+βo,sec, with the phase transformation α→β temperature (Tβ) = 1311 °C, phase transformation γ→β temperature of (Tγsolv) = 1231 °C, phase transformation α2→α or βo→β temperature (Tα2→α/Tβo→β) = 1168 °C, eutectoid temperature (Teut) = 1132 °C and Tα2/γ→βo,sec≈1120 °C. In comparison with Ti-42Al alloy, the Teut and Tγsolv are slightly increased while both the Tβ is decreased obviously by 5% Mn addition. When quenched from the temperature of 1380-1260 °C, the martensitic transformation β→α′ could occur to form the needlelike martensite structure in β area. This kind of martensitic structure is much obvious with the increase of temperature from 1260 °C to 1380 °C. When the temperature is below Tγsolv (1231 °C), the γ grains would nucleate directly from the β phase. For the temperature slightly lower than Teut (1132 °C), the dotted βo,sec phases could nucleate in the lamellar colonies besides the γ lamellae precipitated within α2 phase. Finally, at room-temperature (RT), the alloy exhibits (βo2+γ) triple phase with microstructure of βo+lamellae+γ, of which the lamellar structure consists of α2, γ and βo,sec phases. The phase transformation mechanisms in this alloy, involving β→α′, β→γ, α2→α2/γ and α2→βo,sec were discussed.

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    Foam structure to improve microwave absorption properties of silicon carbide/carbon material
    Li Wanchong, Li Chusen, Lin Lihai, Wang Yan, Zhang Jinsong
    J. Mater. Sci. Technol.. 2019, 35 (11): 2658-2664.   DOI: 10.1016/j.jmst.2019.05.060
    Abstract   HTML   PDF (3893KB)

    Foam structure materials are well known for their lightweight, efficient, and broadband microwave absorption properties compared to bulk material. However, little has been understood about the effect of a foam structure on the absorption performance of the foam material. In this study, the role of foam structure properties of the silicon carbide/carbon (SiC/C) foam material on microwave absorption is explored using experiment and simulation. We find that the foam structure of SiC/C foam material causes diffraction, multiple reflections, improves the interfacial polarization, and compatibilization. The absorption performance of SiC/C foam material is also studied. The -10 dB effective absorption bandwidth can be adjusted from 4.0 GHz to 18 GHz by tuning SiC/C foam material thickness to 3-7 mm. Therefore, the foam structure design is an effective way to improve the absorption performance of the SiC/C foam material.

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    Formation and evolution of layered structure in dissimilar welded joints between ferritic-martensitic steel and 316L stainless steel with fillers
    Liu Guoliang, Yang Shanwu, Ding Jianwen, Han Wentuo, Zhou Lujun, Zhang Mengqi, Zhou Shanshan, Misra R.D.K., Wan Farong, Shang Chengjia
    J. Mater. Sci. Technol.. 2019, 35 (11): 2665-2681.   DOI: 10.1016/j.jmst.2019.05.047
    Abstract   HTML   PDF (14033KB)

    Dissimilar high-energy beam (HEB) welding is necessary in many industrial applications. Different composition of heat-affected zone (HAZ) and weld metal (WM) lead to variation in mechanical properties within the dissimilar joint, which determines the performance of the welded structure. In the present study, appropriate filler material was used during electron beam welding (EBW) to obtain a reliable dissimilar joint between reduced-activation ferritic-martensitic (RAFM) steel and 316 L austenitic stainless steel. It was observed that the layered structure occurred in the weld metal with 310S filler (310S-WM), which had the inferior resistance to thermal disturbance, leading to severe hardening of 310S-WM after one-step tempering treatment. To further ameliorate the joint inhomogeneity, two-step heat treatment processes were imposed to the joints and optimized. δ-ferrite in the layered structure transformed into γ-phase in the first-step normalizing and remained stable during cooling. In the second-step of tempering, tempered martensite was obtained in the HAZ of the RAFM steel, while the microstructure of 310S-WM was not affected. Thus, the optimized properties for HAZ and 310S-WM in dissimilar welded joint was both obtained by a two-step heat treatment. The creep failure position of two dissimilar joints both occurred in CLAM-BM.

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    Development of new endovascular stent-graft system for type B thoracic aortic dissection with finite element analysis and experimental verification
    Zhou Xiaochen, Yang Fan, Gong Xiaoyan, Zhao Ming, Zheng Yufeng, Sun Zhili
    J. Mater. Sci. Technol.. 2019, 35 (11): 2682-2692.   DOI: 10.1016/j.jmst.2019.07.007
    Abstract   HTML   PDF (4052KB)

    Endovascular repair of the thoracic aorta with self-expanding stent-grafts has been emerging as a less invasive alternative treatment compared with conventional open surgeries. Despite the promising efficacy and safety of endovascular stent grafting, the stent-graft failure remains a major concern in terms of stent migration, device fatigue, and the risk of endoleaks. Challenges associated with the stent-grafts involve optimized geometrical structure, lifetime fatigue resistance, and adequate radial support. In this work, a novel endovascular stent-graft system is developed specially for the treatment of Stanford type B thoracic aortic dissections (TAD). Numerical study with finite element analysis (FEA) was utilized to evaluate the mechanical behaviors of the individual stent component. Results of the simulation were validated by experimental tests. Based on the systematic analysis of the parametric variations, a final stent-graft system was developed by the selection and arrangement of the individual stent components, targeting an optimal performance for treatment of TAD. The optimized solution of the stent-graft system was tested in clinical trials, showing advantageous therapeutic efficacy.

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    Lightning ablation suppression of aircraft carbon/epoxy composite laminates by metal mesh
    Wang F.S., Zhang Y., Ma X.T., Wei Z., Gao J.F.
    J. Mater. Sci. Technol.. 2019, 35 (11): 2693-2704.   DOI: 10.1016/j.jmst.2019.07.010
    Abstract   HTML   PDF (6819KB)

    Three-dimensional finite element (FE) models of carbon/epoxy composite laminates with copper mesh and aluminum mesh protection were established subjected to lightning strike, in which different mesh spacing was selected. Effectiveness of numerical method was verified and impulse current waveforms with different current peaks were applied according to aircraft lightning zones. Thermal-electrical material parameters varying with temperature were added into numerical models. Element deletion method was used to deal with lightning ablation elements of composite structures. The results show that ablation area and depth of composite laminates with metal mesh protection are significantly smaller, which proves good protection effectiveness of metal meshes on anti-lightning strike. The denser the mesh spacing, the better the anti-lightning strike will be. Protection of composite laminates with copper mesh has better effects than that of aluminum mesh. Considering the effect of mesh spacing variation on composite structural weight and anti-lightning strike, the ideal mesh spacing was obtained.

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    Influence of laser surface remelting on microstructure and degradation mechanism in simulated body fluid of Zn-0.5Zr alloy
    Zheng Wang, Qingke Zhang, Robabeh Bagheri, Pushan Guo, Yirong Yao, Lijing Yang, Zhenlun Song
    J. Mater. Sci. Technol.. 2019, 35 (11): 2705-2713.   DOI: 10.1016/j.jmst.2019.05.019
    Abstract   HTML   PDF (6086KB)

    In this study, the Zn-0.5 wt%Zr (Zn-Zr) alloy was treated by laser surface remelting (LSR), and then the microstructure and degradation mechanism of the remelting layer were investigated and compared with the original as-cast alloy. The results reveal that after LSR, the bulky Zn22Zr phase in the original Zn-Zr alloy is dissolved and the coarse equiaxed grains transform into fine dendrites with a secondary dendrite arm space of about 100 nm. During the degradation process in simulated body fluid (SBF), the corrosion products usually concentrate at some certain areas in the original alloy, while the corrosion products distribute uniformly and loosely in the LSR-treated surface. After removing the corrosion products, it was found that the former suffers obvious pitting corrosion and then localized corrosion. The proposed mechanism is that corrosion initiates at grain boundaries and develops into the depth at some locations, and then leads to localized corrosion. For the LSR-treated sample, corrosion initiates at some active sites and propagates in all directions, corrosion takes place in the whole surface with distinctly uniform thickness reduction, while the localized corrosion and peeling of bulky Zn22Zr particles were eliminated. The electrochemical results also suggest the uniform corrosion of LSR-treated sample and localized corrosion of original sample. Based on the results, a new approach to regulate the corrosion mode of the biodegradable Zn alloy is proposed.

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    Research Article
    Dislocation-mediated migration of nterphase boundaries
    Zhipeng Sun, Fuzhi Dai, Ben Xu, Wenzheng Zhang
    J. Mater. Sci. Technol.. 2019, 35 (11): 2714-2726.   DOI: 10.1016/j.jmst.2019.05.052
    Abstract   HTML   PDF (4407KB)

    Faceted interphase boundaries (IPBs) are commonly observed in lath-shaped precipitates in alloys consisting of simple face-centred cubic (fcc), body centred-cubic (bcc) or hexagonal closed packed (hcp) phases, which normally contain one or two sets of parallel dislocations. The influence of these dislocations on interface migration and possible accompanying long-range strain field remain unclear. To elucidate this, we carried out atomistic simulations to investigate the dislocation-mediated migration processes of IPBs in a pure-iron system. Our results show that the migration of these IPBs is accompanied with the slip of interfacial dislocations, even in high-index slip planes, with two migration modes were observed: the first mode is the uniform migration mode that occurs only when all of the dislocations slip in a common slip plane. A shear-coupled interface migration was observed for this mode. The other interfaces propagate in the stick-slip migration mode that occurs when the dislocations glide on different slip planes, involving dislocation reaction or tangling. A quantitative relationship was established to link the atomic displacements with the dislocation structure, slip plane, and interface normal. The macroscopic shear deformation due to the effect of overall atomic displacement shows a good agreement with the results obtained based on the phenomenological theory of martensite crystallography. Our findings have general implications for the understanding of phase transformations and the surface relief effect at the atomic scale.

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    Orginal Article
    Osteogenesis stimulation by copper-containing 316L stainless steel via activation of akt cell signaling pathway and Runx2 upregulation
    Yonghui Yuan, Shujing Jin, Xun Qi, Xudong Chen, Wei Zhang, Ke Yang, Hongshan Zhong
    J. Mater. Sci. Technol.. 2019, 35 (11): 2727-2733.   DOI: 10.1016/j.jmst.2019.04.028
    Abstract   HTML   PDF (1729KB)

    As a metallic orthopedic implant, 316 L stainless steel (316 L SS) is used extensively for its good resistance to corrosion and mechanical properties. However, it takes a long time to achieve osseointegration between 316 L SS and adjacent tissues due to its bio-inert characteristic. Hence, the aim is to improve the bio-adaption of 316 L SS. A good approach is to add elements to materials to improve their osteogenic capabilities by the appropriate release of ions. Hence copper-containing 316 L stainless steel (316L-Cu SS) was investigated in this work, where Cu is an essential trace element that can stimulates osteogenesis. It was found that 316L-Cu SS was bio-safe and did not affect the proliferation of co-cultured osteoblasts in comparison with 316 L SS. It increased cell apoptosis on day 1 but inhibited it on day 3, which cooperates with new bone formation processes. Osteoblasts extend themselves more quickly and in a better manner on the surface of 316L-Cu SS, wheneven more pseudopodia are present. Furthermore, the gene expression of alkaline phosphatase, collagen I and runt-related transcription factor 2 (Runx2) in osteoblasts cultured with 316L-Cu SS was significantly enhanced. Runx2 protein expression increased, and osteogenesis was stimulated by 316L-Cu SS via an Akt cell signaling pathway. In conclusion, 316L-Cu SS stimulates osteogenesis through activation of the Akt cell signaling pathway and the upregulation of Runx2. Thus, 316L-Cu SS is a promising material that may be used in surgical implants to stimulate osteogenesis.

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    Fabrication, characterization and optimization of high conductivity and high quality nanocrystalline molybdenum thin films
    Anil K.Battu, Nanthakishore Makeswaran, C.V. Raman
    J. Mater. Sci. Technol.. 2019, 35 (11): 2734-2741.   DOI: 10.1016/j.jmst.2019.05.023
    Abstract   HTML   PDF (2804KB)

    The present study investigated the influence of substrate temperature (Ts) and working pressure (PAr) on tailoring the properties of nanocrystalline (nc) molybdenum (Mo) films fabricated by radio-frequency magnetron sputtering. The structural, morphological, electrical and optical properties of nc-Mo films were evaluated in detail. The Mo films exhibited (110) orientation with average crystallite size varying from 9 to 22 (±1) nm on increasing Ts. Corroborating with structural data, the electrical resistivity decreased from 55 μΩ cm to 10 μΩ cm, which is the lowest among all the Mo films. For Mo films deposited under variable PAr, the (110) peak intensity decrement coupled with peak broadening on increasing PAr. Lower deposition pressure yielded densely packed thin films with superior structural properties along with low resistivity of $\widetilde{1}$ 5 μΩ cm. Optimum conditions to produce high quality Mo films with excellent structural, morphological, electrical and optical characteristics for utilization in solar cells as back contact layers were identified.

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