Started in 1985 Semimonthly
ISSN 1005-0302
CN 21-1315/TG
Impact factor:6.155

The journal has been awarded the excellent periodical in China, and its articles are covered by SCI, EI, CA, SA, JST, RJ, CSA, MA, EMA, AIA etc., PASCAL web. ISI web of Science,SCOPUS.

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      01 April 2020, Volume 42 Issue 0 Previous Issue    Next Issue
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    Orginal Article
    Hierarchical microstructure of a titanium alloy fabricated by electron beam selective melting
    Jixin Yang, Yiqiang Chen, Yongjiang Huang, Zhiliang Ning, Baokun Liu, Chao Guo, Jianfei Sun
    J. Mater. Sci. Technol., 2020, 42 (0): 1-9.  DOI: 10.1016/j.jmst.2019.09.015
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    Here, a near alpha-type Ti6.5Al2Zr1Mo1V alloy has been fabricated by electron beam selective melting (EBSM). Near-equiaxed grains existed in the first few layers, whereas elongated columnar prior β grains almost parallel to the building direction formed in the subsequent built layers. Interspacing of β phase gradually decreased as the build height increased. Martensite α′ with twins and dislocations emerged and microhardness value reached the maximum in the top region, whereas only α/β phase appeared in other regions in the EBSMed sample. Multiple phase transformations can be observed with the change of peak temperatures during each thermal cycle. With a sufficient dwell time, martensite α′ in the middle and bottom regions in-situ decomposed into α + β and coarsened by the heat conduction from the subsequent layers. Fine β precipitates nucleated heterogeneously inside α′ plates and at plate-plate interfaces during the subsequent EBSM process. Considering the phase transformation during the heating process and the cooling process, the existence time of different phases was combined with cycle heating and cooling to clarify the dynamic evolution of microstructure under complex thermal history of EBSM, favoring the fabrication of high-performance titanium alloy components.

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    In-situ formed NiS/Ni coupled interface for efficient oxygen evolution and hydrogen evolution
    Chaoyi Yan, Jianwen Huang, Chunyang Wu, Yaoyao Li, Yuchuan Tan, Luying Zhang, Yinghui Sun, Xiaona Huang, Jie Xiong
    J. Mater. Sci. Technol., 2020, 42 (0): 10-16.  DOI: 10.1016/j.jmst.2019.08.042
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    High-performance electrocatalysts for water splitting are desired due to the urgent requirement of clean and sustainable hydrogen production. To reduce the energy barrier, herein, we adopt a facile in-situ surface modification strategy to develop a low-cost and efficient electrocatalyst for water splitting. The synthesized mulberry-like NiS/Ni nanoparticles exhibit excellent catalytic performance for water splitting. Small overpotentials of 301 and 161 mV are needed to drive the current density of 10 mA cm-2 accompanying with remarkably low Tafel slopes of 46 and 74 mV dec-1 for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. Meanwhile, a robust electrochemical stability is demonstrated. Further high-resolution X-ray photoelectron spectroscopy analyses reveal that the intrinsic HER activity improvement is attributed to the electron-enriched S on the strongly coupled NiS and Ni interface, which simultaneously facilitates the important electron transfer, consistent with the electrochemical impedance results. The post characterizations demonstrate that surface reconstructed oxyhydroxide contributes to the OER activity and NiS/Ni is an OER precatalyst. This structure construction with in-situ formation of active interface provides an effective way to design efficient electrocatalysts for energy conversion.

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    Microstructural evolution and deformation behavior of copper alloy during rheoforging process
    Miao Cao, Qi Zhang, Ke Huang, Xinjian Wang, Botao Chang, Lei Cai
    J. Mater. Sci. Technol., 2020, 42 (0): 17-27.  DOI: 10.1016/j.jmst.2019.09.036
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    A complete rheo-forming process was carried out to investigate the rheoforging process of C3771 lead brass valve, starting from the semi-solid billet preparation to rheoforging experiments and material performance tests. The near-spherical micro-grains with mean equivalent diameter of 56.3 μm, shape factor of 0.78 were obtained when the raw C3771 lead brass were rotary swaged to a radial strain of 0.22 and then heated to 895 °C for 5 min. The Forge 3D software was used to analyze the temperature, strain and strain rate distribution of copper valve for obtain the reasonable process parameters during the subsequent rheoforging process. The experiment results showed that near-spherical micro-grains were stretched and refined to about 35.7-43.4 μm in different positions due to the dynamic recrystallization during the rheoforging process. The cap thread and nut thread failure torque of the so-produced valve are also discovered to be higher than the traditionally forged copper valve with dendrite micro-grains, with an enhancement of the cap and thread failure torque of 42.2 % and 28 %, respectively.

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    Aluminum doping for optimization of ultrathin and high-k dielectric layer based on SrTiO3
    Ji-Ye Baek, Duy Le Thai, Lee Sang Yeon, Hyungtak Seo
    J. Mater. Sci. Technol., 2020, 42 (0): 28-37.  DOI: 10.1016/j.jmst.2019.12.006
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    An ultrathin SrTiO3 dielectric layer is optimized through Al doping to solve the problems existing in development of ultra-high-k oxide MOS capacitors. Through post-deposition annealing, Al doping induces changes in the electronic structure of SrTiO3, thereby effectively reducing leakage current to <10-8 A/cm2 at 0.5 MV/cm but maintains good capacitance values (ε > 80) of ultrathin SrTiO3 MOS capacitors.
    Strontium titanate (SrTiO3) is a high-k material but its bandgap is smaller than that of other oxide dielectrics (e.g., SiO2, Al2O3). Consequently, an ultrathin SrTiO3 film may have a high tunneling leakage current, which is not suitable for capacitor-based applications. To improve the performance of metal-oxide-semiconductor (MOS) capacitors using SrTiO3, an approach based on homogenous and uniform aluminum doping to SrTiO3 through co-sputtering is introduced. The bandgap of a pristine SrTiO3 film showed an increase of 0.5 eV after Al doping. Furthermore, Al doping decreased the leakage current of SrTiO3/Si-based MOS capacitors by more than five orders of magnitude (at the level of nanoampere per square centimeter). Importantly, a dielectric constant of 81.3 and equivalent oxide thickness less than 5 Å were achieved in an 8-nm-thick Al-doped SrTiO3 film owing to changes in its crystal structure and conduction band edge electronic structure. Thus, the obtained data show the effectiveness of the proposed approach for solving the problems existing in the development of ultra-high-k oxide MOS capacitors.

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    Room-temperature synthesis of ZrSnO4 nanoparticles for electron transport layer in efficient planar hetrojunction perovskite solar cells
    Noh Young Wook, Jin In Su, Park Sang Hyun, Jung Jae Woong
    J. Mater. Sci. Technol., 2020, 42 (0): 38-45.  DOI: 10.1016/j.jmst.2019.11.008
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    The interface engineering plays a key role in controlled optoelectronic properties of perovskite photovoltaic devices, and thus the electron transport layer (ETL) material with tailored optoelectronic properties remains a challenge for achieving high photovoltaic performance of planar perovskite solar cells (PSCs). Here, the fine and crystalline zirconium stanate (ZrSnO4) nanoparticles (NPs) was synthesized at low temperature, and its optoelectronic properties are systematically investigated. Benefiting from the favorable electronic structure of ZrSnO4 NPs for applications in ETL, efficient electron transport and extraction with suppressed charge recombination are achieved at the interface of perovskite layer. As a result, the optimized ZrSnO4 NPs synthesized at room-temperature deliver the optimized power conversion efficiency up to 16.76 % with acceptable stability. This work opens up a new class of ternary metal oxide for the use in ETL of the planar PSCs and should pave the way toward designing new interfacial materials for practical optoelectronic devices.

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    High-performance carbon fiber/gold/copper composite wires for lightweight electrical cables
    Tran Thang Q., Yoong Lee Jeremy Kong, Amutha Chinnappan, Loc Nguyen Huu, Tran T. Long, Dongxiao Ji, W.A.D.M. Jayathilaka, Kumar Vishnu Vijay, Seeram Ramakrishna
    J. Mater. Sci. Technol., 2020, 42 (0): 46-53.  DOI: 10.1016/j.jmst.2019.08.057
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    In this study, we synthesized high-performance Carbon Fiber/ Gold/ Copper (CF/Au/Cu) composite wires by using a 2-step deposition method via sputtering and electrodeposition. After Au was sputtered on PAN-based CFs as a pre-treatment, the wettability and surface reactivity of the CFs were improved, resulting in a homogeneous deposition of Cu on their surface. At different Cu electrodeposition time, the resulting CF/Au/Cu composite wires could possess a high strength of up to 3.27 GPa (~ 10 times stronger than copper wires) while their electrical conductivity could be as high as 4.4×105 S/cm (~ 75 % of that for copper). More importantly, since the composite wires were lightweight (up to 70 % lower than Cu mass density), they are a promising candidate to substitute conventional heavy metal wires in the future electrical applications.

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    Improved electron capture capability of field-assisted exponential-doping GaN nanowire array photocathode
    Lei Liu, Feifei Lu, Sihao Xia, Yu Diao, Jian Tian
    J. Mater. Sci. Technol., 2020, 42 (0): 54-62.  DOI: 10.1016/j.jmst.2019.10.014
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    The exponential-doping GaN nanowire arrays (GaN NWAs) photocathode has a “light-trapping effect”, and the built-in electric field can promote the concentration of the photogenerated carrier center to the top surface of the nanowire. However, in the preparation of actual NWAs photocathodes, the problem that photons emitted from the sides of the nanowires cannot be effectively collected has been encountered. Our proposed field-assisted exponential-doping GaN NWAs can bend the motion trajectory of the emitted electrons toward the collecting side. In this study, the quantum efficiency (QE) and collection efficiency (CE) of the external field-assisted exponential-doping GaN NWAs photocathode are derived based on the two-dimensional carrier diffusion equation and the initial energy and angular distribution, respectively. For a field-assisted exponential-doping GaN NWAs with a width d = 200 nm and a height H = 400 nm, the optimal structural parameters are obtained: the incident angle θ = 50° and the nanowire spacing is L = 335.6 nm. On this basis, the field intensity of 0.5 V/μm can maximize the CE of the NWAs. All the results show that the field-assisted approach does contribute to the collection of emitted electrons, which can provide theoretical guidance for high-performance electron sources based on exponential-doping GaN NWAs photocathodes. And field-assisted exponential-doping GaN NWAs cathode is expected to be verified by the experimental results in the future.

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    Microstructure and fracture toughness of the Bridgman directionally solidified Fe-Al-Ta eutectic at different solidification rates
    Chunjuan Cui, Cong Wang, Pei Wang, Wei Liu, Yuanyuan Lai, Li Deng, Haijun Su
    J. Mater. Sci. Technol., 2020, 42 (0): 63-74.  DOI: 10.1016/j.jmst.2019.09.041
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    Fe-Al-Ta eutectic composites were obtained by a modified Bridgman directional solidification technique at different solidification rates. Solidification microstructure transforms from regular eutectic to eutectic colony with the increase of the solidification rate. The solid/liquid interface of Fe-Al-Ta eutectic evolves from planar interface to cellular interface with the increase of the solidification rate. In addition, three-point bending method was adopted to study the room-temperature fracture toughness of the as-cast Fe-Al-Ta eutectic alloy and the Fe-Al-Ta eutectic composites. Moreover, the fracture morphologies, the crack propagation path and the strengthening mechanism of Fe-Al-Ta eutectic were discussed.

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    Visualization of microstructural factors resisting the crack propagation in mesosegregated high-strength low-alloy steel
    Shuxia Wang, Chuanwei Li, Lizhan Han, Haozhang Zhong, Jianfeng Gu
    J. Mater. Sci. Technol., 2020, 42 (0): 75-84.  DOI: 10.1016/j.jmst.2019.05.075
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    While relationship between fracture mechanism and homogeneous microstructures has been fully understood, relationship between fracture mechanism and inhomogeneous microstructures such as the mesosegregation receives less attention as it deserves. Fracture mechanism of the high-strength low-alloy (HSLA) steel considering the mesosegregation was investigated and its corresponding microstructure was characterized in this paper. Mesosegregation refers to the inhomogeneous distribution of alloy elements during casting solidification, and leads to the formation of positive segregation zones (PSZ) and negative segregation zones (NSZ) in ingots. The fracture surface of impact sample exhibits the quasi-cleavage fracture at -21 °C, and is divided into ductile and brittle fracture zone. Meanwhile, the PSZ and NSZ spread across ductile and brittle fracture zone randomly. In ductile fracture zone, micro-voids fracture mechanism covers the PSZ and NSZ, and higher deformation degree is shown in the PSZ. In brittle fracture zone, secondary cleavage cracks are observed in both PSZ and NSZ, but present bigger size and higher quantity in the NSZ. However, some regions of the PSZ still present micro-voids fracture mechanism in brittle fracture zone. It reveals that the microstructures in the PSZ exhibit a higher resistance ability to crack propagation than that in the NSZ. All observations above provide a better visualization of the microstructural factors that resist the crack propagation. It is important to map all information regarding the fracture mechanism and mesosegregation to allow for further acceptance and industrial use.

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    Effect of environments and normal loads on tribological properties of nitrided Ni45(FeCoCr)40(AlTi)15 high-entropy alloys
    L.W. Lan, X.J. Wang, R.P. Guo, H.J. Yang, J.W. Qiao
    J. Mater. Sci. Technol., 2020, 42 (0): 85-96.  DOI: 10.1016/j.jmst.2019.08.051
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    The tribological properties of nitrided Ni45(FeCoCr)40(AlTi)15 high-entropy alloys (HEAs) were investigated in air and simulated acid rain under different normal loads (5, 7, 10, and 12 N) at ambient temperature. The results revealed that as-cast HEAs were only composed of FCC phase, while the volume fraction of FCC phase in the nitrided alloys was significantly reduced. Moreover, the hard phases of AlN, CrN, Fe4N, and TiN phases were formed in the nitrided alloys. The thickness of the nitriding layer was about 8.4 μm. The hardness increased from 8.7 GPa in as-cast alloys to 14.5 GPa in the nitrided alloys. In addition, under the same conditions, the friction coefficient of the nitrided alloys was higher than that of as-cast alloys, but the wear rate was generally lower than that of as-cast alloys. Furthermore, the wear rate of the nitrided alloys was the lowest in acid rain due to the lubrication, cleaning, and cooling in the liquid environment. In air, dominating wear mechanisms in as-cast and nitrided alloys were abrasive, delamination, and adhesive wears. And, the wear mechanism of as-cast and nitrided alloys in acid rain was mainly abrasive and corrosion wears.

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    Oxide dispersion strengthened stainless steel 316L with superior strength and ductility by selective laser melting
    Yuan Zhong, Leifeng Liu, Ji Zou, Xiaodong Li, Daqing Cui, Zhijian Shen
    J. Mater. Sci. Technol., 2020, 42 (0): 97-105.  DOI: 10.1016/j.jmst.2019.11.004
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    Dense oxide dispersion strengthened (ODS) 316 L steels with different amount of Y2O3 additions were successfully fabricated by selective laser melting (SLM) even though part of the added Y2O3 got lost during the process. The microstructure was characterized in details and the mechanical properties were tested at room temperature, 250 °C and 400 °C, respectively. The effect of the scanning speed on agglomeration of nanoparticles during SLM process was discussed. Superior properties, e.g., yield strength of 574 MPa and elongation of 91 %, were achieved at room temperature in SLM ODS 316 L with additional 1 % of Y2O3. At elevated temperatures, the strength kept high but the elongations dropped dramatically. It was observed that nano-voids nucleated throughout the whole gauge section at the sites where nanoinclusions located. The growth and coalescence of these voids were suppressed by the formation of an element segregation network before necking, which relieved local stress concentration and thus delayed necking. This unusual necking behavior was studied and compared to the previous theory. It appeared that the strong convection presented in the melt pool can evenly redistribute the short-time milled coarse Y2O3 precursor powder during SLM process. These findings can not only solve the problems encountered during the fabrication of ODS components but also replenish the strengthening mechanism of SLM 316 L thus pave a way for further improving of mechanical properties.

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    Structure and magnetic properties of YCo5 compound at high pressures
    E. Burzo, P. Vlaic, D.P. Kozlenko, N.O. Golosova, S.E. Kichanov, B.N. Savenko, A. Ostlin, L. Chioncel
    J. Mater. Sci. Technol., 2020, 42 (0): 106-112.  DOI: 10.1016/j.jmst.2019.12.001
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    The crystal structure and magnetic properties of YCo5 compound have been studied by neutron diffraction, in the pressure range 0 ≤ p ≤ 7.2 GPa. The cobalt moments decrease with pressure, parallelly with anisotropic changes of lattice parameters. The experimental data are analyzed together with results from the combined Density Functional and Dynamical Mean-Field Theory. A rather good agreement between the experimentally determined and calculated values of cobalt moments is shown. Our scenario for the behavior of YCo5 under pressure, is the combined action of the Lifshitz transition with a strong local electron-electron interaction.

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    Microstructure evolution and superelasticity behavior of Ti-Ni-Hf shape memory alloy composite with multi-scale and heterogeneous reinforcements
    Xiaoyang Yi, Bin Sun, Weihong Gao, Xianglong Meng, Zhiyong Gao, Wei Cai, Liancheng Zhao
    J. Mater. Sci. Technol., 2020, 42 (0): 113-121.  DOI: 10.1016/j.jmst.2019.09.027
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    In the present study, the in-situ TiB whisker was introduced into the Ti-Ni-Hf shape memory alloy composite by the in-situ reaction of the Ti-Ni-Hf alloy powder and TiB2 powders. The (Ti,Hf)2Ni phase also precipitated, accompanied with the formation of TiB phase. Moreover, the residual TiB2 particles can be observed, as the TiB2 content was higher than 0.7 wt%. Thereinto, the larger scale reinforcements constituted the quasi-continuous network structure. The smaller scale reinforcements distributed in the interior of the network structure. The two-scale reinforcements showed the uniform distribution at macroscopic level and inhomogeneous distribution at microscopic level. The single stage B19′↔B2 martensitic transformation occurred in the Ti-Ni-Hf composites. In addition, the martensitic transformation temperatures continuously decreased with the increased TiB2 content owing to the compositional and mechanical effect. The moderate TiB2 addition not noly enhanced the matrix strength, but also significantly improved the superelasticity. The excellent superelaticity with the completely recoverable strain of 4 % can be obtained in the Ti-Ni-Hf composite containing 0.7 wt% TiB2.

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    Effect of cooling rate upon the microstructure and mechanical properties of in-situ TiC reinforced high entropy alloy CoCrFeNi
    Jifeng Zhang, Ting Jia, Huan Qiu, Heguo Zhu, Zonghan Xie
    J. Mater. Sci. Technol., 2020, 42 (0): 122-129.  DOI: 10.1016/j.jmst.2019.12.002
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    Three types of in-situ TiC (5 vol%, 10 vol% and 15 vol%) reinforced high entropy alloy CoCrFeNi matrix composites were produced by vacuum induction smelting. The effect of two extreme cooling conditions (i.e., slow cooling in furnace and rapid cooling in copper crucible) upon the microstructure and mechanical properties was examined. In the case of slow cooling in the furnace, TiC was found to form mostly along the grain boundaries for the 5 vol% samples. With the increase of TiC reinforcements, fibrous TiC appeared and extended into the matrix, leading to an increase in hardness. The ultimate tensile strength of the composites shows a marked variation with increasing TiC content; that is, 425.6 MPa (matrix), 372.8 MPa (5 vol%), 550.4 MPa (10 vol%) and 334.3 MPa (15 vol%), while the elongation-to-failure (i.e., ductility) decreases. The fracture pattern was found to transit from the ductile to cleavage fracture, as the TiC content increased. When the samples cooled rapidly in copper crucible, the TiC particles formed both along the grain boundaries and within the grains. With the increase of TiC volume fraction, both the hardness and ultimate tensile strength of the resulting composites improved steadily while the elongation-to-failure declined. Therefore, the fast cooling can be used to drastically improve the strength of in-situ TiC reinforced CoCrFeNi. For example, for the 15 vol% TiC/CoCrFeNi composite cooled in the copper crucible, the hardness and ultimate tensile strength can reach as high as 595 HV and 941.7 MPa, respectively.

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    Modification of Mn on corrosion and mechanical behavior of biodegradable Mg88Y4Zn2Li5 alloy with long-period stacking ordered structure
    Jiaxin Zhang, Jinshan Zhang, Fuyin Han, Wei Liu, Longlong Zhang, Rui Zhao, Chunxiang Xu, Jing Dou
    J. Mater. Sci. Technol., 2020, 42 (0): 130-142.  DOI: 10.1016/j.jmst.2019.09.038
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    The biological corrosion behavior and mechanical properties of Mg89-xY4Zn2Li5Mnx (x = 0, 0.5, 1, 1.5 and 2 at.%) alloy with long-period stacking ordered (LPSO) structure were investigated in this work. The magnesium matrix and the eutectic phase of Mg88Y4Zn2Li5Mn1 alloy are effectively refined by the grain boundary segregation of Mn, and the average size of matrix and the eutectic phase decreased by 66 % and 74 %, respectively. The ultimate tensile strength (UTS) and elongation enhanced by 36 % and 55 %, respectively. The corrosion rates obtained by weight loss and hydrogen evolution of Mg88Y4Zn2Li5Mn1 alloy were 79 % and 84 % lower than that of Mg88Y4Zn2Li5 alloy. Additionally, Mg88Y4Zn2Li5Mn1 alloy also presents superior corrosion behavior in electrochemical test. It is verified that Mn plays a positive role in both corrosion and mechanical properties of the Mg88Y4Zn2Li5Mn1 alloy, which provides a reference for further experimental work.

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    Influence of N on precipitation behavior, associated corrosion and mechanical properties of super austenitic stainless steel S32654
    Shucai Zhang, Huabing Li, Zhouhua Jiang, Zhixing Li, Jingxi Wu, Binbin Zhang, Fei Duan, Hao Feng, Hongchun Zhu
    J. Mater. Sci. Technol., 2020, 42 (0): 143-155.  DOI: 10.1016/j.jmst.2019.10.011
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    The influence of N on the precipitation behavior, associated corrosion, and mechanical properties of S32654 were investigated by microstructural, electrochemical, and mechanical analyses. Increasing the N content results in several alterations: (1) grain refinement, which promotes intergranular precipitation; (2) a linear increase in the driving force for Cr2N and Mo activity, which accelerates the precipitation of intergranular Cr2N and π phase, respectively; (3) a linear decrease in the driving force for σ phase and Cr activity, which suppresses the formation of intragranular σ phase. The total amount of precipitates first decreased and then increased with the N content increasing. Furthermore, the intergranular corrosion susceptibility depended substantially on the total amount of precipitates and also first exhibited a decreasing and then an increasing trend as the N content increased. In addition, aging precipitation caused a considerable decrement in the ultimate tensile strength (UTS) and a remarkable increment in the yield strength (YS). Both the UTS and YS always increased with N content increasing throughout the solution and aging process. Whereas the elongation was considerably sensitive to the aging treatment, it exhibited marginal variation with the N content increasing.

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    One-dimensional Ag2S/ZnS/ZnO nanorod array films for photocathodic protection for 304 stainless steel
    Na Wei, Yuan Lin, Zhenkui Li, Wenxia Sun, Guosong Zhang, Mingliang Wang, Hongzhi Cui
    J. Mater. Sci. Technol., 2020, 42 (0): 156-162.  DOI: 10.1016/j.jmst.2019.09.035
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    Highly ordered Ag2S/ZnS/ZnO nanorod array film photoanodes were prepared on a Ti substrate for photocathodic cathodic protection. The results indicated that the photoresponse range of the Ag2S/ZnS/ZnO composite film was extended compared to those of the ZnO and ZnS/ZnO films, indicating its higher light absorption capacity. When the Ag2S/ZnS/ZnO composite film served as a photoanode, the film can provide the best effective photocathodic protection for 304 stainless steel in a 3.5 wt% NaCl solution under white light illumination compared to the ZnO and ZnS/ZnO films. Additionally, in comparison to pure ZnO film, the photocurrent for the ZnS/ZnO film remained the same without noticeable fluctuation after illumination for 1 h, indicating that the ZnS functionalization improved the stability by overcoming the photocorrosion effect of the ZnO photoanode under light irradiation.

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    Role of welding residual strain and ductility dip cracking on corrosion fatigue behavior of Alloy 52/52M dissimilar metal weld in borated and lithiated high-temperature water
    Jun Gao, Jibo Tan, Ming Jiao, Xinqiang Wu, Lichen Tang, Yifeng Huang
    J. Mater. Sci. Technol., 2020, 42 (0): 163-174.  DOI: 10.1016/j.jmst.2019.10.012
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    Corrosion fatigue behavior of Alloy 52/52M dissimilar metal weld (DMW) was investigated in borated and lithiated high-temperature water. The fatigue life of Alloy 52/52M DMW in high-temperature water decreased in comparison with that in air. The fatigue cracks initiated at Alloy 52M butt weld or at the interface of Alloy 52 buttering and Alloy 52M butt weld. The welding residual strain and ductility dip cracking in Alloy 52M butt weld promoted the initiation and propagation of fatigue cracks. The environmentally assisted fatigue damage in high-temperature water is discussed by taking account of microstructure defects.

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    The texture and its optimization in magnesium alloy
    Jialin Wu, Li Jin, Jie Dong, Fenghua Wang, Shuai Dong
    J. Mater. Sci. Technol., 2020, 42 (0): 175-189.  DOI: 10.1016/j.jmst.2019.10.010
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    he crystallographic orientations are generally non-random in wrought Mg alloy, which will lead to their macroscopic physical properties to be anisotropic. Understanding the texture evolution in processing of Mg alloy billets and its effect on mechanical properties is therefore an important project for all scientists and engineers in material area. This paper is concerned with the description of texture, with the mechanisms of texture evolution and with the interrelationships between texture and mechanical properties in Mg alloy. It is a full review of understanding of the basic mechanism on texture evolution, of texture altering by alloying or processing, and of the mechanism of texture weakening. Moreover, it provides theories necessary and available techniques to develop high-performance Mg wrought with optimized texture in the field.

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    Grain size and temperature effect on the tensile behavior and deformation mechanisms of non-equiatomic Fe41Mn25Ni24Co8Cr2 high entropy alloy
    H.T. Jeong, W.J. Kim
    J. Mater. Sci. Technol., 2020, 42 (0): 190-202.  DOI: 10.1016/j.jmst.2019.09.034
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    The effect of the grain size on the tensile properties and deformation mechanisms of a nonequiatomic Fe41Mn25Ni24Co8Cr2 high-entropy alloy was studied in the temperature range between 298 and 1173 K by preparing the samples with three different grain sizes through severe plastic deformation and subsequent annealing: ultrafine (sub)grain size (≤0.5 μm), 8.1 μm and 590.2 μm. In the temperature between 298 and 773 K, the material with the large grain size of 590.2 μm exhibited the largest tensile ductility (57 %-82 %) due to its high strain hardening associated with mechanical twinning, but it exhibited the lowest strength due to its large grain size. The material with the ultrafine (sub)grain size exhibited the lowest tensile ductility (3 %-7 %) due to a greatly reduced strain hardening ability after severe plastic deformation, but it exhibited the highest strength due to the dislocation strengthening and grain refinement strengthening. At tensile testing at temperatures above 973 K, recrystallization occurred in the material with the ultrafine (sub)grains during the sample heating and holding stage, leading to the formation of fine and equiaxed grains with the sizes of 6.8-13.5 μm. The deformation behavior of the Fe41Mn25Ni24Co8Cr2 with different grain sizes in the high temperature range between 973 and 1173 K, where pseudosteady-state flow was attained in the stress-strain curves, could be explained by considering the simultaneous contribution of grain boundary sliding and dislocation-climb creep to total plastic flow. The activation energies for plastic flow for the materials with different grain sizes were similar as ~199 kJ/mol. In predicting the deformation mechanism, it was important to consider the change in grain size by rapid grain growth or recrystallization during the sample heating and holding stage because grain boundary sliding is a grain-size-dependent deformation mechanism. The sample with the ultrafine (sub)grains exhibited the large tensile elongations of 30 %-85 % due to its high strain rate sensitivity, m (0.1-0.5) at temperatures of 973-1173 K. The material with the large grain size of 590.2 μm exhibited the very small elongations of 0.2 %-8 % due to its small m values (0.1-0.2) and occurrence of brittle intergranular fracture at the early stage of plastic deformation.

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    Enhanced crystallization resistance and thermal stability via suppressing the metastable superlattice phase in Ni-(Pd)-P metallic glasses
    Qing Du, Xiongjun Liu, Yihuan Cao, Yuren Wen, Dongdong Xiao, Yuan Wu, Hui Wang, Zhaoping Lu
    J. Mater. Sci. Technol., 2020, 42 (0): 203-211.  DOI: 10.1016/j.jmst.2019.11.005
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    Virtually, glass formation is to avoid crystallization during solidification, i.e., a consequence of the competition between the undercooled liquid and primary crystalline phases. It is found that the crystallization resistance of the binary Ni-P system was drastically enhanced with alloying of Pd and correspondingly, the critical size for glass formation increased significantly from the micrometer to millimeter scale. Thermodynamically, the introduction of Pd could effectively increase the atomic size mismatch and heat of mixing, which are beneficial to stabilize the supercooled liquid. Kinetically, the introduction of Pd not only successfully suppresses the formation of metastable superlattice phase, which is prone to nucleation and growth in the supercooled liquid state, but also changes the crystallization mechanism from the primary to eutectic mode. The current finding sheds light on understanding glass formation of the most studied Pd-Ni-P system and the glass-forming ability in general.

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    Composition dependent intrinsic defect structures in ASnO3 (A = Ca, Sr, Ba)
    Yuchen Liu, Yu Zhou, Dechang Jia, Juanli Zhao, Banghui Wang, Yuanyuan Cui, Qian Li, Bin Liu
    J. Mater. Sci. Technol., 2020, 42 (0): 212-219.  DOI: 10.1016/j.jmst.2019.10.015
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    Perovskite stannates are promising semiconductors that are widely used in optoelectronic devices. Here, the composition dependent intrinsic point defects of stannate perovskites ASnO3 (A = Ca, Sr, Ba) are studied by first-principles calculations. The preferences of defects under stoichiometric and nonstoichiometric conditions are unsealed, meanwhile the charge states of each intrinsic defect varying with the change of electron Fermi energy are clarified. For stoichiometric BaSnO3 and SrSnO3, the Schottky defect complexes are predicted as the most stable defect structure, while the antisite defect complexes are the most stable one in CaSnO3. In nonstoichiometric ASnO3, excessive AO is beneficial to the formation of oxygen vacancies and A-Sn antisite defects in all ASnO3; while the Ca interstitial is another major defect existing in CaSnO3. In the case of SnO2 excess, the predominant defects are the Sn-A antisite defects and A vacancies. Since the functionality of these perovskite oxides is closely related to the types and concentrations of their point defects, the present results are expected to guide the future experiments to optimize the function of the perovskite oxides by tailoring the intrinsic defects through controlling the composition of AO and SnO2.

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    Influencing mechanism of pre-existing nanoscale Al5Fe2 phase on Mg-Fe interface in friction stir spot welded Al-free ZK60-Q235 joint
    R.Z. Xu, Q. Yang, D.R. Ni, B.L. Xiao, C.Z. Liu, Z.Y. Ma
    J. Mater. Sci. Technol., 2020, 42 (0): 220-228.  DOI: 10.1016/j.jmst.2019.12.003
    Abstract   HTML   PDF

    Al-free ZK60 magnesium (Mg) alloy sheet was selected as substrate material of Mg-steel pinless friction stir spot welding (FSSW), avoiding the effect of the Al element in the substrate on the alloying reaction of Mg-iron (Fe) interface. The sound FSSW joint of ZK60 Mg alloy and Q235 steel with a hot-dipped aluminum (Al)-containing zinc (Zn) coating was successfully realized. The detailed microstructural examinations proved that Al5Fe2 phase at the Mg-Fe interface came from the pre-existing Al5Fe2 phase in the coating and acted as the transition layer for promoting the metallurgical bonding of Mg and Fe. The interfaces with well-matched lattice sites among Fe, Al5Fe2 and Mg were formed during FSSW. A low energy interface with good match of lattice sites ((002)Al5Fe2//(110)Fe, [110]Al5Fe2//[$\bar{1}$13]Fe) between Al5Fe2 and Fe was identified. For the interface between Al5Fe2 and Mg, an orientation relationship of (6$\bar{2}$2)Al5Fe2//(3$\overline{112}$)Mgand[1$\overline{58}$]Al5Fe2//[2$\bar{4}$23]Mg was observed. The tensile-shear load of the ZK60-steel joint could reach 4.6 kN. Moreover, the joint fracture occurred at the interface between the Al5Fe2 layer and the Mg alloy substrate, suggesting the brittle fracture characteristic.

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    CALTPP: A general program to calculate thermophysical properties
    Yuling Liu, Cong Zhang, Changfa Du, Yong Du, Zhoushun Zheng, Shuhong Liu, Lei Huang, Shiyi Wen, Youliang Jin, Huaqing Zhang, Fan Zhang, George Kaptay
    J. Mater. Sci. Technol., 2020, 42 (0): 229-240.  DOI: 10.1016/j.jmst.2019.12.005
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    A program CALTPP (CALculation of ThermoPhysical Properties) is developed in order to provide various thermophysical properties such as diffusion coefficient, interfacial energy, thermal conductivity, viscosity and molar volume mainly as function of temperature and composition. These thermophysical properties are very important inputs for microstructure simulations and mechanical property predictions. The general structure of CALTPP is briefly described, and the CALPHAD-type models for the description of these thermophysical properties are presented. The CALTPP program contains the input module, calculation and/or optimization modules and output module. A few case studies including (a) the calculation of diffusion coefficient and optimization of atomic mobility, (b) the calculation of solid/liquid, coherent solid/solid and liquid/liquid interfacial energies, (c) the calculation of thermal conductivity, (d) the calculation of viscosity, and (e) the establishment of molar volume database in binary and ternary alloys are demonstrated to show the features of CALTPP. It is expected that CALTPP will be an effective contribution in both scientific research and education.

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    Transition of dynamic recrystallization mechanism during hot deformation of Incoloy 028 alloy
    XiTing Zhong, Lei Wang, LinKe Huang, Feng Liu
    J. Mater. Sci. Technol., 2020, 42 (0): 241-253.  DOI: 10.1016/j.jmst.2019.08.058
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    Dynamic recrystallization (DRX) plays significant roles in manipulating of microstructures during hot deformation and the result mechanical properties; however, the underling mechanism leading to multi scale-microstructures remains poorly understood. Here, the DRX mechanism under wide processing conditions (i.e. 950-1200 °C, 0.001-10 s-1) in Incoloy 028 alloy was investigated, where the relationships among flow stress, Z parameter and grain size, as well as the evolution of characteristic microstructures (grain size, sub-grain boundaries, and high angle grain boundaries), are established. As the values of Z parameters decrease (corresponding to decreased flow stresses), three typical softening mechanisms successively occur, ranging from continuous DRX controlled by dislocation glide, discontinuous DRX dominated by dislocation motion (climb and cross/multiple slip) and grain boundary migration, to dynamic normal/abnormal grain growth resulting from grain boundary migration, with transition regions where two adjacent mechanisms occur simultaneously. Correspondingly, these above three softening mechanisms result in ultrafine, fine and coarse grains, respectively. The present findings demonstrate a comprehensive understanding of DRX mechanism over a wide range of processing conditions, and further provide a new guideline for preparing single crystals.

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CN: 21-1315/TG
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