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CN 21-1315/TG
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Current Issue
 01 September 2020, Volume 52 Issue 0 Previous Issue    Next Issue
Research Article
 Select Effects of AlCoCrFeNiTi high-entropy alloy on microstructure and mechanical properties of pure aluminum Qinglin Li, Shang Zhao, Xuepeng Bao, Yushi Zhang, Yuqian Zhu, Chuangzao Wang, Yefeng Lan, Yuxin Zhang, Tiandong Xia J. Mater. Sci. Technol., 2020, 52 (0): 1-11.  DOI: 10.1016/j.jmst.2020.04.008 A new kind of AlCoCrFeNiTi high-entropy alloy (HEA) as a grain refiner was prepared by vacuum arc melting. In this work, the effects of HEA (1.0 wt.%, 2.0 wt.% and 3.0 wt.%) on the microstructure and mechanical properties of pure aluminum were studied. The microstructure was characterized and examined by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), electron probe micro-analyzer (EPMA) and transmission electron microscopy (TEM) to indicate the refining abilities and mechanism of HEA on pure aluminum. Results show that the addition of HEA refined both the macrostructure and microstructure of pure aluminum. When 1.0 wt.% HEA was added, most coarse columnar grains were refined into equiaxed crystals, and as the amount of HEA increased to 2.0 wt.% and 3.0 wt.%, aluminum grains were further refined, and the grain boundaries were nearly indistinguishable. Moreover, the morphology of α-Al transformed from coarse columnar crystals to equiaxed grains, and the mean size of α-Al grains decreased from 374 μm to 27 μm. The Al3Ti, Al3Ni, and nano-phase precipitated from the aluminum alloy with HEA in the solidification. The typical rod-like nano-phases distributed interdendritic regions of α-Al. The average length of nano-phases is 2568 nm, 4372 nm, and 6907 nm and the average diameter is 112 nm, 103 nm, and 92 nm when 1.0 wt.%, 2.0 wt.% and 3.0 wt.% HEA were added to the pure aluminum, respectively. The ultimate tensile strength (UTS) and yield strength (YS) were improved in all samples, whereas the elongation (El) was decreased with increasing HEA concentration. When 3.0 wt.% HEA was added into the aluminum melt, the UTS was improved by 145.2% from 62 MPa to 152 MPa, the YS was increased by 173.8% from 42 MPa to 115 MPa, and the El was decreased by 33.3% from 39% to 26%.
 Select Reduced interface energy loss in non-fullerene organic solar cells using room temperature-synthesized SnO2 quantum dots InSu Jin, Minwoo Park, Jae Woong Jung J. Mater. Sci. Technol., 2020, 52 (0): 12-19.  DOI: 10.1016/j.jmst.2020.02.054 We herein report the room temperature synthesis of colloidal SnO2 quantum dots and their application in non-fullerene organic solar cells as an excellent electron transport layer. The thiourea-assisted hydrolysis at room temperature affords the nanocrystalline SnO2 quantum dots with a diameter of 3-4 nm. The utilization of the SnO2 quantum dots as an electron transporting layer effectively reduces the interfacial trap density and charge recombination in the solar cell devices, leading to not only the reduced energy loss but also excellent photocurrent generation. The optimized organic solar cells employing SnO2 quantum dots with polyethylenimine ethoxylated achieves power conversion efficiencies up to 12.023 % with a VOC, a JSC, and a FF of 0.89 V, 18.89 mA cm -2, and 0.72. This work suggest that the SnO2 quantum dot is a promising electron transporting material to construct efficient organic solar cells for practical applications. This work also demonstrates the key strategy for thiourea-assisted hydrolysis to synthesize fine and nanocrystalline SnO2 quantum dots.
 Select Mechanical and thermal properties of RETaO4 (RE = Yb, Lu, Sc) ceramics with monoclinic-prime phase Lin Chen, Mingyu Hu, Jun Guo, Xiaoyu Chong, Jing Feng J. Mater. Sci. Technol., 2020, 52 (0): 20-28.  DOI: 10.1016/j.jmst.2020.02.051 As candidate thermal/environmental barrier coatings (T/EBCs), the structure characteristics and comprehensive properties of monoclinic-prime (m') RETaO4 (RE = Yb, Lu, Sc) with excellent Al2O3/SiO2 chemical compatibility are studied. Excellent thermal insulation protection will be provided by m'RETaO4 due to their low thermal conductivity (～1.6 W m -1 K -1, 900 °C) and prominent thermal radiation resistance, which is much better than those of YSZ (～2.5 W m -1 K -1, 1000 °C) and La2Zr2O7 (～2.0 W m -1 K -1, 900 °C). The thermal expansion coefficients (TECs) are 3.0-8.0 × 10 -6 K -1 (200-1200 °C), which is suitable for T/EBCs applications. Furthermore, absence of phase transition and extraordinary chemical compatibility with Al2O3/SiO2 up to 1500 °C indicate the potential application prospect. The documented governing mechanisms of m'RETaO4 properties will enable researchers to promote their application in the future investigation.
 Select Recent progresses on designing and manufacturing of bulk refractory alloys with high performances based on controlling interfaces T. Zhang, H.W. Deng, Z.M. Xie, R. Liu, J.F. Yang, C.S. Liu, X.P. Wang, Q.F. Fang, Y. Xiong J. Mater. Sci. Technol., 2020, 52 (0): 29-62.  DOI: 10.1016/j.jmst.2020.02.046 Refractory alloys such as tungsten and molybdenum based alloys with high strength, thermal/electrical conductivity, low coefficient of thermal expansion and excellent creep resistances are highly desirable for applications in nuclear facilities, critical components in aerospace and defense components. However, the serious embrittlement limits the engineering usability of some refractory alloys. A lot of research results indicate that the performances of refractory alloys are closely related to the physical/chemical status, such as the interface dimension, interface type, interface composition of their grain boundaries (GBs), phase boundaries (PBs) and other interface features. This paper reviewed the recent progress of simulations and experiments on interface design strategies that achieve high performance refractory alloys. These strategies include GB interface purifying/strengthening, PB interface strengthening and PB/GB synergistic strengthening. Great details are provided on the design/fabrication strategy such as GB interface controlling, PB interface controlling and synergistic control of multi-scaled interfaces. The corresponding performances such as the mechanical property, thermal conductivity, thermal load resistance, thermal stability, irradiation resistance, and oxidation resistance are reviewed in the aspect to the effect of interfaces. In addition, the relationships between these interfaces and material properties are discussed. Finally, future developments and potential new research directions for refractory alloys are proposed.
 Select Self-assembling anchored film basing on two tetrazole derivatives for application to protect copper in sulfuric acid environment Yujie Qiang, Hao Li, Xijian Lan J. Mater. Sci. Technol., 2020, 52 (0): 63-71.  DOI: 10.1016/j.jmst.2020.04.005 Two tetrazole compounds (BTA, BTTA) self-assembled on copper substrate and their inhibition effect toward copper corrosion in 0.5 M H2SO4 was evaluated through atomic force microscopy (AFM), scanning electron microscopy (SEM), weight loss measurement along with electrochemical techniques including electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. Results indicate that BTTA can provide superior inhibition performance to BTA, and the highest inhibition efficiency values of 96.3% (BTA) and 99.8% (BTTA) were achieved respectively at 2 mM. Both tetrazole inhibitor films follow Langmuir model concerning both physical and chemical adsorption, which can be verified by X-ray photoelectronic spectroscopy (XPS) analysis. Besides, the negative value of adsorption free energy infers a spontaneous adsorption process of these tetrazole compounds on Cu surface. Molecular dynamics (MD) simulation reveals stronger multiple anchor adsorption of BTTA molecules than BTA because of the existence of S atom.
 Select Microstructure and mechanical properties of large-scale Mg-Gd-Y-Zn-Mn alloys prepared through semi-continuous casting Kui Wang, Jingfeng Wang, Xiaoxu Dou, Yuanding Huang, Norbert Hort, Sarkis Gavras, Shijie Liu, Yanwu Cai, Jinxing Wang, Fusheng Pan J. Mater. Sci. Technol., 2020, 52 (0): 72-82.  DOI: 10.1016/j.jmst.2020.04.013 Large-scale Mg-8Gd-4Y-1Zn-Mn (wt.%) alloy ingot with a diameter of 315 mm and a length of 2410 mm was prepared through semi-continuous casting. Chemical composition, microstructure and mechanical properties at different locations of the samples with as-cast, T4 and T6 heat-treated states, respectively, were investigated. No obvious macro segregation has been detected in the high-quality alloy ingot. The main eutectic structures at all different locations are composed of α-Mg, Mg3RE-type, Mg5RE-type and LPSO phases. At the edge of ingot, the unusual casting twins including $\text{ }\!\!\{\!\!\text{ 10}\bar{1}\text{2 }\!\!\}\!\!\text{ }$ extension twins and $\text{ }\!\!\{\!\!\text{ 10}\bar{1}\text{1 }\!\!\}\!\!\text{ }$ compression twins were observed due to the intensive internal stress. In T4 heat-treated alloy, the micro segregation was eliminated. The remained phases were α-Mg and LPSO phase. Combined with the remarkable age-hardening response, T6 samples exhibits improved mechanical properties at ambient temperature, which derives from the dense prismatic β' precipitates and profuse basal γ' precipitates.
 Select In vitro crevice corrosion of biodegradable magnesium in different solutions Bowei Chen, Hongliu Wu, Ruibang Yi, Wenhui Wang, Haidong Xu, Shaoxiang Zhang, Hongzhou Peng, Junwei Ma, Haomiao Jiang, Rui Zan, Shuang Qiao, Yu Sun, Peng Hou, Pei Han, Jiahua Ni, Xiaonong Zhang J. Mater. Sci. Technol., 2020, 52 (0): 83-88.  DOI: 10.1016/j.jmst.2020.04.014 Magnesium (Mg) is a promising biomedical metal because of its biodegradability. The crevice between tissue and Mg implant can not be neglected in some implantation sites due to inducing crevice corrosion of Mg. In this paper, a new single mold was designed to build the in vitro experimental setup and four kinds of solutions, i.e. the deionized water (DW), the 0.9 wt.% sodium chloride solution (NaCl), the phosphate buffer saline (PBS) and the modified simulated body fluid (m-SBF) were used to explore necessary factors of crevice corrosion in Mg. It was observed that crevice corrosion in Mg sheets would occur in NaCl and PBS solution under 0.2, 0.5 and 0.8 mm crevice thickness. And it was found that there were two necessary factors, i.e. chloride ion and crevice dimension, in crevice corrosion. For the high-purity Mg cannulated screws, crevice corrosion could occur inside tunnel when immersed in PBS.
 Select Microstructure and texture evolution of the β-Mg17A12 phase in a Mg alloy with an ultra-high Al content Changjian Yan, Yunchang Xin, Ce Wang, Huan Liu, Qing Liu J. Mater. Sci. Technol., 2020, 52 (0): 89-99.  DOI: 10.1016/j.jmst.2020.04.021 In the present study, the effects of equal channel angular pressing (ECAP) on the microstructure and mechanical property of the Mg-20Al alloy were systematically investigated. For the first time, the texture of Mg17Al12 phase and its evolution with ECAP conditions were reported. The results show that increasing the processing temperature and passes generates more uniform distribution and finer size of β-Mg17Al12 phases. The large pieces of β-Mg17Al12 phases are composed of many fine grains with different crystallographic orientations. For the β-Mg17Al12 phase, a preferred distribution of (001) appears at 523 K and 573 K, and hardly varies with temperature. Nevertheless, a random texture is observed at 623 K. The (0002) poles exhibit a preferred distribution at 473 K, but this preferred distribution varies with temperature. A random distribution of (0002) poles is observed when processed at 623 K. Many types of crystallographic planar relationship between β-Mg17Al12 phase and α-Mg matrix are observed and the relationships of {11$\bar{2}$3}//{100} or {110} or {111} and {12$\bar{1}$1}//{100} or //{110} or {111} have a relatively higher frequency than others. The texture of α-Mg matrix is much different from that of the ECAPed Mg alloys with a relative low Al content, in which a texture with basal poles inclining approximately 45° away from the extrusion direction often develops. The mechanical properties of Mg-20Al alloy are closely related to the temperature and passes of ECAP. A higher temperature often decreases the yield strength, but hardly alters the maximum strength. There is a low plasticity for all the samples and increasing processing temperature slightly enhances the plasticity. The corresponding mechanisms were deeply discussed.
 Select Superhydrophobic coatings for corrosion protection of magnesium alloys Wenhui Yao, Liang Wu, Guangsheng Huang, Bin Jiang, Andrej Atrens, Fusheng Pan J. Mater. Sci. Technol., 2020, 52 (0): 100-118.  DOI: 10.1016/j.jmst.2020.02.055 Magnesium (Mg) alloys show great potential to be extensively applied in practice owing to their superior properties, while the poor corrosion resistance does undoubtedly restrict their applications. Superhydrophobic coatings with good repellency to corrosive solutions can significantly decrease the interaction between the corrosive species and the substrate, so that they are receiving a lot of attention to improve the corrosion resistance of Mg alloys. Various strategies have been introduced to develop a superhydrophobic coating on Mg alloys, which were reviewed to elucidate the current research status to provide a clue or thinking for beginning researchers. Further, the existing issues of superhydrophobic coating were discussed, especially for their real applications in practice, mainly owing to their poor mechanical stability. Based on the existing issues, the future study was discussed to improve the stability of hierarchical structures and entrapped air pockets, impart the superhydrophobic coating self-healing property to repair the damaged area during service, provide double protection by incorporation of corrosion inhibitors, or even introduce slippery liquid-infused porous surfaces with lubricant layer to provide better corrosion protection for Mg alloys.
 Select Lightweight and robust rGO/sugarcane derived hybrid carbon foams with outstanding EMI shielding performance Lei Wang, Xuetao Shi, Junliang Zhang, Yali Zhang, Junwei Gu J. Mater. Sci. Technol., 2020, 52 (0): 119-126.  DOI: 10.1016/j.jmst.2020.03.029 Increasingly severe electromagnetic pollution is now in urgent need of materials with lightweight, excellent flame retardancy, and outstanding electromagnetic interference shielding effectiveness (EMI SE). Renewable source-derived carbon foams and graphene have attracted extensive attention due to their 3D porous structure and remarkable electrical conductivity (σ). In this work, annealed sugarcane (ASC) was prepared by removal of lignin from sugarcane via hydrothermal reaction, followed by annealing treatment. Then graphene oxide (GO) was filled by vacuum-assisted impregnation process and thermally annealed to obtain the ASC/reduced graphene oxide (rGO) hybrid foams. When the loading of rGO is 17 wt.%, the ASC/rGO hybrid foam (density, ρ of 0.047 g/cm 3) exhibits the optimal σ of 6.0 S/cm, EMI SE of 53 dB, specific SE (SSE = SE/ρ)/thickness (t) of 3830 dB·cm 2/g, and compressive strength of 1.33 MPa, which is 76%, 36%, 13% and 6% higher than those of ASC, respectively. Moreover, ASC/rGO presents excellent flame retardancy, thermal stability, and heat insulation, which remains constant under burning on an alcohol lamp and presents low thermal conductivity of 115.19?mW(m·K), close to the requirement for heat insulation. Synergistic effect of ASC and rGO not only significantly increase σ of ASC/rGO, but fully utilizes the capability of ASC and rGO to attenuate electromagnetic waves by virtue of unique porous structures and abundant interfaces. Such kind of lightweight EMI materials with excellent mechanical property, shielding performance, flame retardancy, and heat insulation is expected to tackle the key scientific and technical bottleneck problems of EMI materials, and will greatly expand the application of carbon nanomaterials in the field of aerospace industry.
 Select Effect of Cu on Martensite Transformation of CoCrMo alloy for biomedical application Ruoxian Wang, Gaowu Qin, Erlin Zhang J. Mater. Sci. Technol., 2020, 52 (0): 127-135.  DOI: 10.1016/j.jmst.2020.04.012 The martensite transformation of Co-29Cr-6Mo-xCu (Co-xCu, x=0,1.5,2,4 , wt%) alloys was investigated in order to explore ductile Co-based alloy without Ni for biomedical application. The effect of Cu on martensite transformation of Co-29Cr-6Mo alloy was investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-Ray diffraction (XRD) and electron backscatter diffraction (EBSD) analysis. EBSD results revealed that the fraction of γ-phase was increasing with increasing of copper content. In detail, the fraction of γ-phase of aged Co-1.5Cu alloy was 4.72% and no γ-phase was found in aged Co-0Cu alloy. Furthermore, the fraction of γ-phase of aged Co-2Cu alloy and Co-4Cu alloy was 51.68% and 46.17%, respectively. This demonstrated that the minimum Cu content which could inhibit martensite transformation in this alloy system was 2 wt%. Calculated phase diagram revealed that increasing the copper content of this alloy system could enlarge γ-phase zone, which means Cu could inhibit the formation of ε-phase and consequently stabilize γ-phase. Randomly distributed Cu-rich phase was identified in aged Co-4Cu alloy. The possible reason for the inhibition of martensite transformation by Cu addition is that alloying with Cu atom might decrease charge accumulations and increase atomic bonds, which increase the stacking fault energy ultimately.
 Select Excellent Terahertz shielding performance of ultrathin flexible Cu/graphene nanolayered composites with high stability Shengyue Hou, Wenle Ma, Guanghao Li, Yi Zhang, Yunyun Ji, Fei Fan, Yi Huang J. Mater. Sci. Technol., 2020, 52 (0): 136-144.  DOI: 10.1016/j.jmst.2020.04.007 Electromagnetic interference (EMI) shielding at Terahertz (THz) frequency range attracts increasing attention due to the rapid development of THz science and technologies. EMI shielding materials with small thickness, high shielding effectiveness (SE), good flexibility and stability are highly desirable. Herein, an ultrathin flexible copper/graphene (Cu/Gr) nanolayered composite are prepared, which can reach the average EMI SE of 60.95 dB at 0.1-1.0 THz with a thickness of only 160 nm, indicating that more than 99.9999% of the THz wave power can be shielded. Furthermore, the Cu/Gr nanolayered composite also exhibits excellent oxidation resistance, with a 93.09% maintenance rate for EMI SE value after heating at 120 °C for 3 h in air, far higher than that of the bare Cu film (62.15%). Besides, the Cu/Gr nanolayered composite exhibits good mechanical flexibility and flexural fatigue resistance. The EMI SE value of the Cu/Gr nanolayered composite shows a maintenance rate of 98.87% even after 1500 times bending cycles, obviously higher than that of multilayer Cu film (93.07%). These results demonstrate that the ultrathin flexible Cu/Gr nanolayered composites with excellent shielding performance and good stability have a broad application prospect in THz shielding for wearable devices and next generation mobile communication equipment.
 Select S-scheme photocatalyst Bi2O3/TiO2 nanofiber with improved photocatalytic performance Rongan He, Haijuan Liu, Huimin Liu, Difa Xu, Liuyang Zhang J. Mater. Sci. Technol., 2020, 52 (0): 145-151.  DOI: 10.1016/j.jmst.2020.03.027 In this study, a hierarchical Bi2O3/TiO2 fibrous composite was in-situ fabricated on an electrospun TiO2 nanofiber at ambient temperature. In the Bi2O3/TiO2 composite, S-scheme electron migration occurred between Bi2O3 and TiO2. In the photocatalytic degradation of phenol under simulated sunlight, the as-prepared Bi2O3/TiO2 nanofibers considerably outperformed Bi2O3 nanoparticles and TiO2 nanofibers. This improvement is contributed by maintaining and effectively utilizing the useful carriers and consuming the useless holes and electrons, realized by the S-scheme heterojunction and hierarchical structure. This study also provides an alternative design fashion for photocatalysts.
 Select Investigation of Portevin-Le Chatelier effect in rolled α-phase Mg-Li alloy during tensile and compressive deformation Xiaoqiang Li, Chunlong Cheng, Qichi Le, Lei Bao, Peipeng Jin, Ping Wang, Liang Ren, Hang Wang, Xiong Zhou, Chenglu Hu J. Mater. Sci. Technol., 2020, 52 (0): 152-161.  DOI: 10.1016/j.jmst.2020.04.022 Avoiding the Portevin-Le Chatelier (PLC) effect is very important concern for wrought Mg-Li alloys. In this study, the special PLC effect was found in rolled Mg-5Li-3Al-2Zn (LAZ532) alloy during tensile and compressive deformation. By observing microstructure evolution of the alloy during tensile and compressive deformation, it was found that prismatic and pyramidal slips were activated during tensile deformation, resulting in plenty of dislocation accumulation. In the deformation process after compressive yielding, the deformations in coarse grains and fine grains were dominated by {10 $\bar{1}$ 2} extension twinning and grain boundary slip, respectively. Based on experimental result analysis, the sudden appearance of PLC effect in the later stage of axial tensile deformation (along rolled direction) was caused by interaction between solute atoms and dislocations. In the process of axial compressive deformation (along rolled direction), PLC effect presented the complex and changeable phenomenon of appeared-disappeared-appeared, which was mainly caused by the continuous nucleation of twin in the material, the activation of grain boundary slip and the shear deformation of twin, respectively.
 Select Microstructure-dependent oxidation behavior of Ni-Al single-crystal alloys Jianlu Pei, Yefan Li, Chong Li, Zumin Wang, Yongchang Liu, Huijun Li J. Mater. Sci. Technol., 2020, 52 (0): 162-171.  DOI: 10.1016/j.jmst.2020.04.006 The effect of the γ′+γ two-phase structure on the oxidation behaviors of Ni-Al single-crystal alloys at 650 °C was investigated by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X-ray diffraction and Auger electron spectroscopy. In the initial oxidation stage, the oxidation behavior is primarily determined by the growth pattern of oxides in the γ channel. The outward convex NiO was formed in unprotected wide γ channels. And Ni-Al spinel oxide provides a great number of short-circuit paths, accelerating the inward diffusion of oxygen and outward diffusion of Ni. In the late stage of oxidation, the elongated internal oxide in the large γ′ phase contributes to the diffusion of oxygen along the oxide/metal interface. Consequently, the Ni-Al single-crystal alloy with wide γ channels and large γ′ precipitates exhibited poor oxidation performance.
 Select Ultrahigh electrical conductivities and low lattice thermal conductivities of La, Dy, and Nb Co-doped SrTiO3 thermoelectric materials with complex structures Daquan Liu, Yanxia Wang, Xue Jiang, Huijun Kang, Xiong Yang, Xiaoying Zhang, Tongmin Wang J. Mater. Sci. Technol., 2020, 52 (0): 172-179.  DOI: 10.1016/j.jmst.2020.02.065 Microstructural modifications and appropriate element doping are necessary to simultaneously enhance the electrical conductivities and reduce the lattice thermal conductivities of thermoelectric materials. Herein, we propose a strategy of multielement doping combined with a burial sintering process to promote thermoelectric properties. Three-element doped Sr0.9La0.05Dy0.05Ti1-xNbxO3 (x = 0, 0.05, 0.10, 0.15, and 0.20) powders were synthesized by high-energy ball milling, and corresponding bulk samples were prepared by carbon burial sintering. In the bulk samples, we obtained the desired microstructures composed of shell-vesicular architectures with dense dislocations and second phase particles. These materials had ultrahigh electrical conductivities (～5300 S cm-1 at 300 K), low lattice thermal conductivities (～1.6 W m-1 K-1 from 700 to 1100 K when x = 0.2) and low total thermal conductivities (minimum value of 2.95 W m-1 K-1 when x = 0.05 at 1100 K). The maximum zT values were 0.28 when x = 0.05 and 0.27 when x = 0.2 at 1100 K. This strategy provides a possible direction for improving the thermoelectric properties of SrTiO3 based materials.
 Select Fatigue properties of titanium alloy custom short stems fabricated by electron beam melting Liao Wang, Shujun Li, Mengning Yan, Yubo Cheng, Wentao Hou, Yiping Wang, Songtao Ai, Rui Yang, Kerong Dai J. Mater. Sci. Technol., 2020, 52 (0): 180-188.  DOI: 10.1016/j.jmst.2020.02.047 The fatigue properties of titanium alloy short-stems with four different lengths, manufactured by electron beam melting (EBM) technology, were investigated by in vitro test and finite element (FE) analysis. FE simulation results indicate that the maximum tensile stress concentrates at the lateral side of the stem body. The magnitude of the concentrated tensile stress increases and the corresponding area of the axial section decreases with increasing of stem length. Results from fatigue tests demonstrate that fatigue cracks mainly initiate from the rough surface of the stem where the maximum tensile stress concentrates. The fatigue strength decreases with the increase of stem length, which is attributed to the higher stress concentration on the longer stem surface. In addition, it is found that post EBM treatment via hot isostatic processing (HIP) is able to enhance the fatigue properties of the stems, since the pores generated during EBM are mostly closed during HIP. Our work also demonstrates that the stress concentration on the stem surface can be effectively mitigated and the corresponding fatigue properties of the EBM-fabricated titanium alloy short stem can be considerably improved by optimizing the design in the stem length.
 Select Effects of Mn content on recrystallization resistance of AA6082 aluminum alloys during post-deformation annealing Xiaoming Qian, Nick Parson, X.-Grant Chen J. Mater. Sci. Technol., 2020, 52 (0): 189-197.  DOI: 10.1016/j.jmst.2020.04.015 The microstructural evolutions under as-homogenized and as-deformed conditions and after the post-deformation annealing of AA6082 aluminum alloys with different Mn content (0.05 wt.%-1 wt.%) were studied by optical, scanning electron, and transmission electron microscopies. The results showed that the presence of a large amount of α-Al(Mn,Fe)Si dispersoids induced by Mn addition significantly improved the recrystallization resistance. In the base alloy free of Mn, static recrystallization occurred after 2 h of annealing, and grain growth commenced after 4 h of annealing, whereas in Mn-containing alloys, the recovered grain structure was well-retained after even 8 h of annealing. The alloy with 0.5% Mn exhibited the best recrystallization resistance, and a further increase of the Mn levels to 1% resulted in a gradual reduction of the recrystallization resistance, the reason for which was that recrystallization occurred only in the dispersoid-free zones (DFZs) and the increased DFZ fraction with Mn content led to an increase in the recrystallization fraction. The variation in the dispersoid number density and a coarsening of dispersoids during annealing have a limited influence on the static recrystallization in Mn-containing alloys.
 Select Inhibition of sulfate-reducing bacteria influenced corrosion on hydrophobic poly(dimethylsiloxane) coatings Innocent O. Arukalam, C.N. Njoku, Lihui Yang, Baorong Hou, Ying Li J. Mater. Sci. Technol., 2020, 52 (0): 198-206.  DOI: 10.1016/j.jmst.2019.06.027 Sulfate-reducing bacteria (SRB) has been pointed out as one of the causative agents of microbial induced corrosion in the marine environment. To address this problem, novel strategies are being experimented as against the earlier methods which have been banned due to their toxic effects on useful aquatic lives. Thus, the aim of this study was to investigate the effect of non-toxic perfluorodecyltrichlorosilane (PFDTS) on resistance of hydrophobic poly(dimethylsiloxane)/phosphoric acid-treated zinc oxide (PDMS/PA-treated ZnO) coatings to SRB-induced biofouling and corrosion. The surface features of the coatings before and after exposure to SRB/NaCl solution were analyzed by scanning electron microscopy (SEM). Wettability of the coatings before and after exposure was also measured. The interaction of SRB with the coatings was investigated by FTIR spectroscopy. The resistance performance of the modified coatings against SRB-induced corrosion was monitored by electrochemical impedance spectroscopy (EIS). The EIS measurements revealed that 0.20 g PFDTS-based coating displayed highest corrosion resistance with impedance modulus of 6.301 × 10 10 after 15 d of exposure to SRB/NaCl medium. The results were corroborated by surface and chemical interaction analyses, and thus, indicate that 0.20 g PFDTS-modified PDMS/PA-treated ZnO coating has potentials for excellent SRB-induced corrosion resistance and anti-biofouling performance.
 Select Melting behavior and globular microstructure formation in semi-solid CoCrCuxFeNi high-entropy alloys Kaio Niitsu Campo, Caio Chaussê de Freitas, Leonardo Fanton, Rubens Caram J. Mater. Sci. Technol., 2020, 52 (0): 207-217.  DOI: 10.1016/j.jmst.2020.04.009 High-entropy alloys can be compelling raw materials for semi-solid applications. In the present study, the influence of the Cu content on the melting behavior and semi-solid microstructure of CoCrCuxFeNi (x = 0, 1, 2, 3) alloys was investigated. Arc-melted samples were cross-rolled at room temperature and then isothermally treated at 1175 °C in the semi-solid state for 300 s. Microstructural characterization showed that the alloys containing Cu were formed by two fcc phases. Notably, the increase in Cu content also led to an increase in the volumetric fraction of the Cu-rich phase. During solidification, this phase, which is the last to form, nucleates and epitaxially grows on the Cu-lean phase. All the studied CoCrCuFeNi alloys exhibited the same melting behavior. The Cu-rich phase melts at approximately 1120 °C, whereas the Cu-lean phase melts at approximately 1350 °C, providing a suitable processing temperature range of more than 200 °C. The semi-solid microstructures were considerably refined and globular regardless of the alloy composition, being suitable for semi-solid processing. Furthermore, each fcc phase exhibited roughly the same composition under the different processing conditions. The Cu content in the Cu-lean phase was approximately 10 at.%, while Co, Cr, Fe, and Ni were in an approximately equiatomic ratio. Meanwhile, the Cu content was between 80 at.% and 86 at.% in the Cu-rich phase. The isothermal treatment of the CoCrCu3FeNi alloy at a higher temperature (1300 °C) only caused the globules to coarsen. In conclusion, this work showed that these alloys can be potential candidates for semi-solid processing.
 Select Nanostructured Ti29.7Ni50.3Hf20 high temperature shape memory alloy processed by high-pressure torsion A. Shuitcev, D.V. Gunderov, B. Sun, L. Li, R.Z. Valiev, Y.X. Tong J. Mater. Sci. Technol., 2020, 52 (0): 218-225.  DOI: 10.1016/j.jmst.2020.01.065 High-pressure torsion (HPT) processing under a pressure of 6.0 GPa was applied to Ti29.7Ni50.3Hf20 (at.%) alloy. Two types of structure were observed after HPT with 3 revolutions: first one is the mixture of amorphous phase and retained nanocrystalline; second is the alternating bands of amorphous phase and high defect density crystalline. As a result, post deformation annealing (PDA) at 500-700 °C leads to the non-uniform distribution of martensite and parent phase grains. The grains of martensite are twice larger compared to that of parent phase. The nanocrystalline and ultrafine grains form after annealing at 500-600 °C and 700 °C, respectively. The twinning mechanism does not change with the reduction of martensitic grains up to ～35 nm. The relationship between strength and grain size in Ti29.7Ni50.3Hf20 alloy obeys the classical Hall-Petch relationship with a coefficient of 10.80 ± 0.39 GPa nm 1/2.
 Select Enhanced interface strength in steel-nickel bimetallic component fabricated using wire arc additive manufacturing with interweaving deposition strategy Bintao Wu, Zhijun Qiu, Zengxi Pan, Kristin Carpenter, Tong Wang, Donghong Ding, Stephen Van Duin, Huijun Li J. Mater. Sci. Technol., 2020, 52 (0): 226-234.  DOI: 10.1016/j.jmst.2020.04.019 Realizing improved strength in composite metallic materials remains a challenge using conventional welding and joining systems due to the generation and development of brittle intermetallic compounds caused by complex thermal profiles during solidification. Here, wire arc additive manufacturing (WAAM) process was used to fabricate a steel-nickel structural component, whose average tensile strength of 634 MPa significantly exceeded that of feedstock materials (steel, 537 MPa and nickel, 455 MPa), which has not been reported previously. The as-fabricated sample exhibited hierarchically structural heterogeneity due to the interweaving deposition strategy. The improved mechanical response during tensile testing was due to the inter-locking microstructure forming a strong bond at the interface and solid solutions strengthening from the intermixing of the Fe and Ni increased the interface strength, beyond the sum of parts. The research offers a new route for producing high-quality steel-nickel dissimilar structures and widens the design opportunities of monolithic components, with site-specific properties, for specific structural or functional applications.
 Select The influence of solute atom ordering on the deformation behavior of hexagonal close packed Ti-Al alloys Hao Wu, Yunlei Xu, Zhihao Wang, Zhenhua Liu, Qinggang Li, Jinkai Li, Junyan Wu J. Mater. Sci. Technol., 2020, 52 (0): 235-242.  DOI: 10.1016/j.jmst.2020.02.064 A framework of compositionally graded Ti-Al alloys was proposed to elucidate the Al alloying dependent deformation mechanism at room temperature. Slip trace analysis demonstrated low-alloyed Ti-Al model materials were plastically deformed by prismatic slip, pyramidal slip, stacking faults, and deformation twins. Increasing Al concentration promoted chemical ordering, thus suppressing the dislocation motion and deformation twinning. The mechanism behind such a kind of composition-mediated deformation physics was discussed. Our findings are expected to be applicable in the design of next-generation high-performance structural materials through the tailoring of the chemical ordering of solute atoms in substitutional solid solution.
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