Started in 1985 Semimonthly
ISSN 1005-0302
CN 21-1315/TG
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Synthesis and photocatalytic performance of ZnO with flower-like structure from zinc oxide ore
Xiaoyi Shen, Hongmei Shao, Yan Liu, Yuchun Zhai
J. Mater. Sci. Technol.    2020, 51 (0): 1-7.   doi:10.1016/j.jmst.2020.01.062
Abstract170)   HTML14)    PDF (2989KB)(98)      

AAAAAEmploying zinc sulfate solution obtained from zinc oxide ore as raw material, sodium hydroxide as precipitant and PEG20000 as dispersant, ultrafine ZnO powders with different morphologies were successfully synthesized through hydrothermal method. The influences of the dosage of PEG20000 solution, molar ratio of OH -/Zn 2+, reaction temperature, reaction time and Zn 2+ concentration on the structures and morphologies of the ZnO powders were discussed in detail. The reaction conditions of synthesizing ZnO powders with flower-like structure were obtained as below: dosage of PEG20000 with 10% mass fraction 5 mL, molar ratio of OH - to Zn 2+ 5, reaction temperature 150 °C, reaction time 8 h at Zn 2+ concentration 1 mol L -1. The growth mechanism of ZnO particles with different morphologies was proposed. The ZnO powder with flower-like structure are composed of multiple micro-rods with hexagon morphology and has good photocatalytic degradation ability to degrade RhB. 20 mL RhB solution with 15 mg L -1 could be completely degraded over flower-like ZnO powder 300 mg within 3 h.

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Cellular automaton modeling of austenite formation from ferrite plus pearlite microstructures during intercritical annealing of a C-Mn steel
Chunni Jia, Chengwu Zheng, Dianzhong Li
J. Mater. Sci. Technol.    2020, 47 (0): 1-9.   doi:10.1016/j.jmst.2020.02.002
Abstract167)   HTML11)    PDF (4092KB)(45)      

A mesoscopic cellular automaton model was developed to study the microstructure evolution and solute redistribution of austenization during intercritical annealing of a C-Mn steel. This model enables a depiction of three-stage kinetics of the transformation combined with the thermodynamic analysis: (1) the rapid austenite growth accompanied with pearlite degeneration until the pearlite dissolves completely; (2) the slower austenite growth into ferrite with a rate limiting factor of carbon diffusion in austenite; and (3) the slow austenite growth in control of the manganese diffusion until the final equilibrium reached for ferrite and austenite. The effect of the annealing temperature on the transformation kinetics and solute partition is also quantitatively rationalized using this model.

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Effects of rare earth on microstructure and impact toughness of low alloy Cr-Mo-V steels for hydrogenation reactor vessels
Zhonghua Jiang, Pei Wang, Dianzhong Li, Yiyi Li
J. Mater. Sci. Technol.    2020, 45 (0): 1-14.   doi:10.1016/j.jmst.2019.03.012
Abstract145)   HTML5)    PDF (6541KB)(61)      

The effects of rare earth (RE) on the microstructure and impact toughness of low alloy Cr-Mo-V bainitic steels have been investigated where the steels have RE content of 0 to 0.048 wt.%. The results indicate that the normalized microstructures of the steels are typical granular bainite (GB) composed primarily of bainitic ferrite and martensite and/or austenite (M-A) constituents. The M-A constituents are transformed into ferrite and carbides and/or agglomerated carbides after tempering at 700 °C for 4 h. The addition of RE decreases the onset temperature of bainitic transformation and results in the formation of finer bainitic ferrite, and reduces the amount of carbon-rich M-A constituents. For the normalized and tempered samples, the ductile-to-brittle transition temperature (DBTT) decreases with increasing RE content to a critical value of 0.012 wt.%. Lower DBTT and higher upper shelf energy are attributed to the decreased effective grain size and lower amount of coarse agglomerated carbides from the decomposition of massive M-A constituents. However, the addition of RE in excess of 0.012 wt.% leads to a substantial increase in the volume fraction of large-sized inclusions, which are extremely detrimental to the impact toughness.

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Effects of ultrasonic assisted friction stir welding on flow behavior, microstructure and mechanical properties of 7N01-T4 aluminum alloy joints
Zhiqiang Zhang, Changshu He, Ying Li, Lei Yu, Su Zhao, Xiang Zhao
J. Mater. Sci. Technol.    2020, 43 (0): 1-13.   doi:10.1016/j.jmst.2019.12.007
Abstract133)   HTML5)    PDF (10012KB)(45)      

Conventional friction stir welding (FSW) and ultrasonic assisted friction stir welding (UAFSW) were employed to weld 6-mm thick 7N01-T4 aluminum alloy plates. Weld forming characteristics and material flow behavior in these two different welding processes were studied and compared. Ultrasonic vibration was applied directly on the weld in axial direction through the welding tool. Metal flow behavior, microstructure characteristics in the nugget zone (NZ) and evolution of the mechanical properties of naturally aged joints were studied. Results show that the ultrasonic vibration can significantly increase the welding speed of defect-free welded joint. At the rotation speed of 1200 rpm, the UAFSW can produce defect-free welded joints at a welding speed that is 50% higher than that of the conventional FSW. Ultrasonic vibrations can also improve surface quality of the joints and reduce axial force by 9%. Moreover, ultrasonic vibrations significantly increase the volume of the pin-driven zone (PDZ) and decrease the thickness of the transition zone (TZ). The number of subgrains and deformed grains resulting from the UAFSW is higher than that from the FSW. By increase the strain level and strain gradient in the NZ, the ultrasonic vibrations can refine the grains. Ultrasonic energy is the most at the top of the NZ, and gradually reduces along the thickness of the plate. The difference in strengths between the FSW and the UAFSW joints after post-weld natural aging (PWNA) is small. However, the elongation of the UAFSW is 8.8% higher than that of the FSW (PWNA for 4320 h). Fracture surface observation demonstrates that all the specimens fail by ductile fracture, and the fracture position of the UAFSW joint changes from HAZ (PWNA for 120 h) to NZ (PWNA for 720 and 4320 h).

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Phase-field simulation of early-stage kinetics evolution of γ' phase in medium supersaturation Co-Al-W alloy
Shujing Shi, Zhengwei Yan, Yongsheng Li, Suleman Muhammad, Dong Wang, Shi Chen, Shengshun Jin
J. Mater. Sci. Technol.    2020, 53 (0): 1-12.   doi:10.1016/j.jmst.2020.02.038
Abstract126)   HTML8)    PDF (6244KB)(53)      

The early precipitation of γ'-Co3(Al, W) phase affects the spatial distribution and kinetic evolution of precipitates for the morphology transmission effect, but the nucleation and concomitant growth are not studied still by aging experiments due to the expeditious precipitation of γ' phase in Co-Al-W alloy. By using the phase-field simulation with sublattice free energy, the early-stage kinetics evolution of γ'-Co3(Al, W) phase in a medium supersaturation Co-9Al-8W (at.%) alloy aged from 1023 K to 1173 K is investigated. The influences of aging temperature on the evolution of morphology and composition of γ' phase, and the kinetics of nucleation and growth to coarsening are clarified. It is found that the rates of composition evolution of W in γ phase are two or three times that of γ' phase, and the W compositions in γ and γ' phases show a linear relationship with time t-1/3, which means that the coarsening takes place earlier at high temperature. In addition, the equilibrium partitioning ratios indicate Al and W partition into the γ' phase and the ratios decrease with elevated temperature. The compositional variations across the γ/γ' phase interfaces suggest that low aging temperature makes the stoichiometric ratio closer to 3:1. Moreover, the precipitation evolutions from early nucleation to growth and coarsening in Co-Al-W alloy are distinguished, and the rate constants of square and cube of average particles radius increase with temperature. In later growth stage, the relationship of the square of average particles radius and time is obeyed, while the steady-state coarsening stage follows the cube law. The time exponents of particles number density at the coarsening stage are close to -1 of Kuehmann-Voorhees (KV) theory. The study demonstrates that the early-stage evolution of γ' phase which is undiscovered in the experiment can be captured by the phase-field simulation, and the resultant kinetics laws agree well with the experimental and theoretical results.

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Resistive switching performance improvement of InGaZnO-based memory device by nitrogen plasma treatment
Li Zhang, Zhong Xu, Jia Han, Lei Liu, Cong Ye, Yi Zhou, Wen Xiong, Yanxin Liu, Gang He
J. Mater. Sci. Technol.    2020, 49 (0): 1-6.   doi:10.1016/j.jmst.2020.01.049
Abstract121)   HTML10)    PDF (2441KB)(25)      

With the demand of flat panel display development, utilizing the non-volatile memory devices based on indium-gallium-zinc-oxide (IGZO) film may be integrated with IGZO thin film transistors (TFTs) to accomplish system-on-panel applications. In this work, 1 × 1 μm2 via hole structure IGZO based memory device was fabricated and the resistive switching (RS) behavior was investigated. By inserting a nitrogen doping layer IGZO:N by plasma treatment in Pt/IGZO/TiN device, highly improved RS performance including lower forming voltage, remarkable uniformity, large memory window of 102, retention property of 104 s at 125 °C, excellent pulse endurance of 107 cycles were achieved. The X-ray photoelectron spectroscopy analysis indicates that plasma doping method can evenly dope nitrogen and induce more non-lattice oxygen in the IGZO film. It is deduced that the N atoms of the inserting layer can influence the random formation of oxygen vacancy type conducting filaments, which results in more stable and uniform performance.

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Inhibition effects of benzalkonium chloride on Chlorella vulgaris induced corrosion of carbon steel
Junlei Wang, Tiansui Zhang, Xinxin Zhang, Muhammed Asif, Lipei Jiang, Shuang Dong, Tingyue Gu, Hongfang Liu
J. Mater. Sci. Technol.    2020, 43 (0): 14-20.   doi:10.1016/j.jmst.2020.01.012
Abstract90)   HTML2)    PDF (2654KB)(27)      

In this work, a surfactant, benzalkonium chloride (BAC), was used to study its effects on both the growth of Chlorella vulgaris and the corrosion caused by its biofilm. Experimental results indicated that BAC at a low concentration of 3 mg/L suppressed C. vulgaris growth and achieved 81 % corrosion inhibition based on weight loss reduction. The inhibition effects increased when the BAC dosage was increased. At 30 mg/L, the corrosion inhibition increased to 95 %. Electrochemical results supported surface pitting analysis, weight loss results data and confirmed the corrosion inhibition.

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Design and development of a high-performance Ni-based superalloy WSU 150 for additive manufacturing
Praveen Sreeramagiri, Ajay Bhagavatam, Abhishek Ramakrishnan, Husam Alrehaili, Guru Prasad Dinda
J. Mater. Sci. Technol.    2020, 47 (0): 20-28.   doi:10.1016/j.jmst.2020.01.041
Abstract85)   HTML5)    PDF (4460KB)(28)      

This research proposes a design and development strategy of a new nickel-based superalloy for additive manufacturing. A new Ni-based superalloy has been developed by the application of the combinatorial alloy development technique coupled with CALPHAD based solidification modeling by effectively suppressing the precipitation kinetics. The suppression of precipitation during processing paved a way for prevention of cracks during deposition. The new alloy “WSU 150″ revealed excellent room temperature mechanical properties with a yield strength of 867 MPa, an ultimate tensile strength of 1188 MPa, and an elongation of 27.9% in the as-deposited condition. The mechanical properties of the heat-treated alloy were improved significantly to 1114 MPa yield strength, 1396 MPa ultimate tensile strength, and an elongation of 16.1%. Improvement in the mechanical properties is attributed to the additional precipitation and coarsening of γ' and carbides during heat-treatment. Microstructural investigation of the alloy revealed spherical γ' with a rippled size distribution from the center to the interdendritic region. The average size of the γ' particles in the as-deposited condition was found to be around 48 nm in the interdendritic region. Heat-treatment promoted the coarsening of γ' which is explained in the paper.

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Microbiologically influenced corrosion of Cu by nitrate reducing marine bacterium Pseudomonas aeruginosa
Yanan Pu, Wenwen Dou, Tingyue Gu, Shiya Tang, Xiaomei Han, Shougang Chen
J. Mater. Sci. Technol.    2020, 47 (0): 10-19.   doi:10.1016/j.jmst.2020.02.008
Abstract77)   HTML5)    PDF (4583KB)(22)      

The microbiologically influenced corrosion (MIC) mechanisms of copper by Pseudomonas aeruginosa as a typical strain of nitrate reducing bacteria (NRB) was investigated in this lab study. Cu was immersed in deoxygenated LB-NO3 seawater inoculated with P. aeruginosa and incubated for 2 weeks. Results showed that this NRB caused pitting and uniform corrosion. The maximum pit depths after 7 d and 14 d in 125 mL anaerobic vials with 50 mL broth were 5.1 μm and 9.1 μm, accompanied by specific weight losses of 1.3 mg/cm2 (7 d) and 1.7 mg/cm2 (14 d), respectively. Electrochemical measurements corroborated weight loss and pit depth data trends. Experimental results indicated that extracellular electron transfer for nitrate reduction was the main MIC mechanism and ammonia secreted by P. aeruginosa could also play a role in the overall Cu corrosion process.

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Zwitterionic glycine modified Fe/Mg-layered double hydroxides for highly selective and efficient removal of oxyanions from polluted water
Xiaofeng Shi, Chao Wang, Jiaoxia Zhang, Li Guo, Jing Lin, Duo Pan, Juying Zhou, Jincheng Fan, Tao Ding, Zhanhu Guo
J. Mater. Sci. Technol.    2020, 51 (0): 8-15.   doi:10.1016/j.jmst.2019.12.034
Abstract76)   HTML6)    PDF (2345KB)(30)      

Zwitterionic glycine was employed to modify Fe/Mg-layered double hydroxides (LDH) to realize an G-Fe/Mg-LDH adsorbent with high adsorption capacities of oxygen-containing anions including As(V), P(V) and Cr(VI). When the Fe/Mg mole ratio was 0.02 mol/0.02 mol, the G-Fe/Mg-LDH has a good adsorption performance. The optimum adsorption pH value of G-Fe/Mg-LDH for oxygen-containing anions was 6. The selectivity of three oxygen-containing anions was Cr(VI)<P(V)<As(V), and the maximum adsorption capacity of As(V) reached as high as 830 mg g -1, outperforming most previously reported efficient adsorbents for As(V). The adsorption process followed Freundlich isotherm and pseudo-second-order kinetic model, suggesting the heterogeneous adsorption and chemical adsorption of the G-Fe/Mg-LDH. When the initial concentration of As(V) was 200 mg L -1, the adsorption efficiency of G-Fe/Mg-LDH was 82.5% within 30 min. This study provides a way to modify the LDHs for environmental remediation.

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Portevin-Le Châtelier effect in wrought Ni-based superalloys: Experiments and mechanisms
Chuanyong Cui, Rui Zhang, Yizhou Zhou, Xiaofeng Sun
J. Mater. Sci. Technol.    2020, 51 (0): 16-31.   doi:10.1016/j.jmst.2020.03.023
Abstract76)   HTML8)    PDF (9168KB)(45)      

The Portevin-Le Chatelier (PLC) effect is a plastic instability in alloys at certain strain rates and deformation temperatures. This plastic instability exhibits serrated yielding in the temporal domain and strain localization in the spatial domain. Wrought Ni-based superalloys often exhibit the PLC effect. To guarantee the safe and stable operation of equipment, it is important to study the PLC effect in wrought Ni-based superalloys. This paper provides a review of various experimental phenomena and micromechanisms related to the PLC effect in wrought Ni-based superalloys, which have been reported in various publications in recent years and include work from our own group. The influences of stacking fault energy and γ′ precipitates on the PLC effect in wrought Ni-based superalloys are also discussed in detail. Additionally, several suggestions for the future study of the PLC effect in wrought Ni-based superalloys are provided.

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Microstructure and tensile properties of DD32 single crystal Ni-base superalloy repaired by laser metal forming
Shiwei Ci, Jingjing Liang, Jinguo Li, Yizhou Zhou, Xiaofeng Sun
J. Mater. Sci. Technol.    2020, 45 (0): 23-34.   doi:10.1016/j.jmst.2020.01.003
Abstract75)   HTML5)    PDF (7715KB)(27)      

In this work, the microstructure and tensile properties of DD32 single-crystal (SC) superalloy repaired by laser metal forming (LMF) using pulsed laser have been studied in detail. The microstructures of the deposited samples and the tensile-ruptured samples were characterized by optical microscopy (OM), transmission electron microscope (TEM) and scanning electron microscope (SEM). Due to high cooling rate, the primary dendrite spacing in the deposited area (17.2 μm) was apparently smaller than that in the substrate area (307 μm), and the carbides in the deposited samples were also smaller compared with that in the substrate area. The formation of (γ+γ′) eutectic in the initial layer of repaired SC was inhibited because of the high cooling rate. As the deposition proceeded, the cooling rate decreased, and the (γ+γ′) eutectic increased gradually. The (γ+γ′) eutectic at heat-affected zone (HAZ) in the molten pool dissolved partly because of the high temperature at HAZ, but there were still residual eutectics. Tensile test results showed that tensile behavior of repaired SC at different temperatures was closely related to the MC carbides, solidification porosity, γ′ phase, and (γ+γ′) eutectic. At moderate temperature, the samples tested fractured preferentially at the substrate area due to the fragmentation of the coarse MC carbide in the substrate area. At elevated temperature, the (γ+γ′) eutectic and solidification porosity in the deposited area became the source of cracks, which deteriorated the high-temperature properties and made the samples rupture at the deposited area preferentially.

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Superhydrophobic diamond-coated Si nanowires for application of anti-biofouling’
Wenjing Long, Haining Li, Bing Yang, Nan Huang, Lusheng Liu, Zhigang Gai, Xin Jiang
J. Mater. Sci. Technol.    2020, 48 (0): 1-8.   doi:10.1016/j.jmst.2019.10.040
Abstract75)   HTML2)    PDF (3956KB)(18)      

The effect of the surface wettability of plasma-modified vertical Si nanowire array on the bio-fouling performance has been investigated. The Si nanowires prepared by a metal-assisted chemical etching technique exhibit a super-hydrophilic surface. The treatment in CH4/H2 gas plasma environment leads to the decoration of graphite and diamond nanoparticles around Si nanowires. The detailed interface between graphite/diamond and Si nanowire was characterized by HRTEM technique. These surface-modified nanowire samples show an increased water contact angle with ultrananocrystalline diamond decorated ones being superhydrophobic. The immersion test in chlorella solution reveals that the diamond-coated Si nanowires possess the least attachment of chlorella in comparison with other Si nanowires. This result confirms that the coating of Si nanowires with diamond nanoparticles shows the best behavior in anti-biofouling. Importantly, this work provides a method fabricated super-hydrophobic surface for the application of biofouling prevention.

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New FeNiCrMo(P, C, B) high-entropy bulk metallic glasses with unusual thermal stability and corrosion resistance
Yanhui Li, Siwen Wang, Xuewei Wang, Meiling Yin, Wei Zhang
J. Mater. Sci. Technol.    2020, 43 (0): 32-39.   doi:10.1016/j.jmst.2020.01.020
Abstract74)   HTML0)    PDF (5137KB)(22)      

New Fe20-35Ni20Cr20-30Mo5-15(P0.6C0.2B0.2)20 bulk metallic glasses with excellent thermal stability, strength, and corrosion resistance have been developed through the high-entropy alloy design strategy. The high-entropy bulk metallic glasses (HE-BMGs) possess larger supercooled liquid regions of ~69 K, higher crystallization onset temperatures of ~852 K, larger undercoolings of ~109 K, and more sluggish crystallization process upon heating than the conventional metallic glass benefited from the high mixing entropy effect. The HE-BMGs also exhibit ultrahigh strength of ~3.4 GPa, Vickers hardness of ~1107, and superior corrosion resistance in acids and NaCl solutions by formation of highly stable Cr- and Mo-enriched passive films. The new metal-metalloid HE-BMG system and exceptional properties give the alloys good promise for both scientific and engineering applications.

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Microstructure evolution, Cu segregation and tensile properties of CoCrFeNiCu high entropy alloy during directional solidification
Huiting Zheng, Ruirun Chen, Gang Qin, Xinzhong Li, Yanqing Su, Hongsheng Ding, Jingjie Guo, Hengzhi Fu
J. Mater. Sci. Technol.    2020, 38 (0): 19-27.   doi:10.1016/j.jmst.2019.08.019
Abstract74)   HTML5)    PDF (6650KB)(21)      

CoCrFeNiCu (equiatomic ratio) samples (ø 8 mm) were directionally solidified at different velocities (10, 30, 60 and 100 μm/s) to investigate the relationship between solidification velocity and microstructure formation, Cu micro-segregation as well as tensile properties. The results indicate that the morphology of the solid-liquid (S-L) interface evolves from convex to planar and then to concave with the increase of solidification velocity. Meanwhile, the primary and the secondary dendritic arm spacings decrease from 100 μm to 10 μm and from 20 μm to 5 μm, respectively. They are mainly influenced by the axial heat transfer and grain competition growth. During directional solidification, element Cu is repelled from the FCC phase and accumulates in the liquid owe to its positive mixing enthalpy with other elements. Tensile testing results show that the ultimate tensile strength (UTS) gradually increases from 400 MPa to 450 MPa, and the strain of the specimen prepared at the velocity of 60 μm/s is higher than those of others. The fracture mode of all specimens is the mixed fracture containing both ductile fracture and brittle fracture, in which ductile fracture plays a fundamental role. In addition, the brittle fracture is induced by Cu segregation. The improvement of UTS is resulted from columnar grain boundary strengthening.

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Comparative study of performance comparison of AlSi10Mg alloy prepared by selective laser melting and casting
Qian Yan, Bo Song, Yusheng Shi
J. Mater. Sci. Technol.    2020, 41 (0): 199-208.   doi:10.1016/j.jmst.2019.08.049
Abstract73)   HTML3)    PDF (4987KB)(23)      

The influence of the microstructure on mechanical properties of AlSi10Mg fabricated by casting and selective laser melting (SLM) were investigated and contrasted in this work, with an emphasis on understanding the forming mechanism. The microstructure, phase structure and mechanical properties were characterized by scanning electron microscopy/field-emission Transmission Electron Microscopy (SEM/TEM), X-Ray Diffraction (XRD), tensile and fatigue tests. The results indicated that the SLM AlSi10Mg exhibited a supersaturated Si network structure precipitated along α-Al cell. Brittle β-Al5FeSi and π-Al8FeMg3Si6 phases were found in the as-cast and SLM AlSi10Mg respectively due to different thermal histories during processing. The SLM AlSi10Mg showed higher tensile strength but lower elongation than the casting, as the result of grain refinement and tortuous crack path. The fatigue results revealed that unmelted powder, oxide inclusion and pores can considerably degrade the fatigue properties for the SLM AlSi10Mg. The SLM process offered a new method for material processing that would avoid harmful Fe-bearing intermetallic compounds and refine the microstructures for enhancing strength.

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(Y0.25Yb0.25Er0.25Lu0.25)2(Zr0.5Hf0.5)2O7: A defective fluorite structured high entropy ceramic with low thermal conductivity and close thermal expansion coefficient to Al2O3
Zifan Zhao, Heng Chen, Huimin Xiang, Fu-Zhi Dai, Xiaohui Wang, Wei Xu, Kuang Sun, Zhijian Peng, Yanchun Zhou
J. Mater. Sci. Technol.    2020, 39 (0): 167-172.   doi:10.1016/j.jmst.2019.08.018
Abstract72)   HTML3)    PDF (2590KB)(49)      
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Microstructure and mechanical properties of (TiZrNbTaMo)C high-entropy ceramic
Kai Wang, Lei Chen, Chenguang Xu, Wen Zhang, Zhanguo Liu, Yujin Wang, Jiahu Ouyang, Xinghong Zhang, Yudong Fu, Yu Zhou
J. Mater. Sci. Technol.    2020, 39 (0): 99-105.   doi:10.1016/j.jmst.2019.07.056
Abstract70)   HTML0)    PDF (3451KB)(93)      

A high-entropy (TiZrNbTaMo)C ceramic has been successfully fabricated by hot pressing the newly-synthesized quinary carbide powder to investigate its microstructure and mechanical properties. The carbothermal reduction process of equimolar quinary metallic oxides at 1500 ℃ for 1 h generates a carbide powder mixture, which consists mainly of TaC- and ZrC-based solid solutions. The as-synthesized powder was then sintered to form a single-phase high-entropy ceramic by a two-step hot pressing at 1850 ℃ for 1 h and 2100 ℃ for 0.5 h, respectively. The high-entropy ceramic exhibits a fine grain size of about 8.8 μm, a high compositional uniformity and a high relative density of 98.6% by adding Mo as the strategic main component. The measured nanohardness values of (TiZrNbTaMo)C ceramic are 25.3 GPa at 9.8 N and 31.3 GPa at 100 mN, respectively, which are clearly higher than those of other available high-entropy carbide ceramics.

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Development of gradient microstructure in the lattice structure of AlSi10Mg alloy fabricated by selective laser melting
Mulin Liu, Naoki Takata, Asuka Suzuki, Makoto Kobashi
J. Mater. Sci. Technol.    2020, 36 (0): 106-117.   doi:10.1016/j.jmst.2019.06.015
Abstract70)   HTML2)    PDF (5822KB)(21)      

To identify the microstructural features of the lattice structures of Al alloys built via the selective laser melting (SLM) process, AlSi10Mg alloy with a body-centered cubic (BCC)-type lattice structure was prepared. Characteristic microstructures comprising melt pools with several columnar α-Al phases with <001 > orientations along the elongation direction and surrounded by eutectic Si particles were observed at all portions of the built lattice structure. In the node portions of the lattice structure, a gradient microstructure (continuous change in microstructure) was observed. The columnar α-Al phases were observed near the top surface of the node portion, whereas they became coarser and more equiaxed near the bottom surface, resulting in softening localized near the bottom surface. In the strut portions of the lattice structure, the columnar α-Al phases were elongated along the inclined direction of struts. This trend was more prevalent near the bottom surface. The α-Al phases became coarser and more equiaxed near the bottom surface as well. The aforementioned results were the basis of a discussion of the development of the gradient microstructure in lattice-structured Al alloys during the SLM process in terms of thermal conductivities at the boundaries between the manufactured (locally melted and rapidly solidified) portions and adjacent (unmelted) alloy powder.

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Cracking behavior and control of β-solidifying Ti-40Al-9V-0.5Y alloy produced by selective laser melting
Piao Gao, Wenpu Huang, Huihui Yang, Guanyi Jing, Qi Liu, Guoqing Wang, Zemin Wang, Xiaoyan Zeng
J. Mater. Sci. Technol.    2020, 39 (0): 144-154.   doi:10.1016/j.jmst.2019.08.026
Abstract68)   HTML2)    PDF (6254KB)(27)      

A β-solidifying Ti-40Al-9V-0.5Y (at.%) alloy with a high cracking sensitivity has been successfully fabricated by selective laser melting (SLM) in this study. The influence factors for cracking sensitivity, cracking behavior and crack inhibition mechanism were investigated. The results show that the effects of process parameters on cracking sensitivity strongly depend on the cooling rate in molten pool with different heat transfer modes. The conduction mode with higher cooling rates exhibits a higher cracking sensitivity in comparison to the keyhole mode. Microstructure characteristics and phase transformations controlled by cooling rate determine the inherent ductility of β-solidifying γ-TiAl alloys during SLM. On this basis, the formation and inhibition mechanism of solidification and cold cracking are proposed. Finally, the crack-free Ti-40Al-9V-0.5Y sample with fine equiaxed microstructures and favorable mechanical properties (microhardness of 542 ± 19 HV, yield strength of 1871 ± 12 MPa, ultimate strength of 2106 ± 13 MPa and ultimate compressive strain of 10.89 ± 0.57%) can be produced by SLM. The strengthening mechanism can be attributed to grain refinement and precipitation strengthening.

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Evaluation of the inhibition behavior of carbon dots on carbon steel in HCl and NaCl solutions
Yuwei Ye, Zilong Jiang, Yangjun Zou, Hao Chen, Shengda Guo, Qiumin Yang, Liyong Chen
J. Mater. Sci. Technol.    2020, 43 (0): 144-153.   doi:10.1016/j.jmst.2020.01.025
Abstract68)   HTML1)    PDF (5061KB)(24)      

An eco-friendly and effective corrosion inhibitor (N-CDs) was acquired by hydrothermal method in methacrylic acid and ethyl(methyl)amine precursors. Afterwards, the weight loss and electrochemistry measurement were chosen to appraise the corrosion inhibition behavior of as-prepared N-CDs for Q235 steel in Cl- contained solutions. The change rules of EIS and Tafel data displayed that the as-prepared N-CDs revealed a high-efficiency protection for steel in all test environments. Meanwhile, the inhibition efficiency of steel reached up to 93.93 % (1 M HCl) and 88.96 % (3.5 wt% NaCl) at 200 mg/L of N-CDs. Furthermore, the N-CDs could form the adsorption film on steel surface to avoid the strong attack of Cl-. By analysis, the adsorption mechanism of as-prepared N-CDs on steel surface was physicochemical interaction, which strictly complied with the Langmuir adsorption model in both solutions.

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Transfer-free CVD graphene for highly sensitive glucose sensors
Shijing Wei, Yabin Hao, Zhe Ying, Chuan Xu, Qinwei Wei, Sen Xue, Hui-Ming Cheng, Wencai Ren, Lai-Peng Ma, You Zeng
J. Mater. Sci. Technol.    2020, 37 (0): 71-76.   doi:10.1016/j.jmst.2019.07.039
Abstract68)   HTML2)    PDF (1683KB)(33)      

Chemical vapor deposition (CVD) graphene film is a promising electrode-modifying material for fabricating high-performance glucose sensor due to its high electrical conductivity and two-dimensional structure over large area. However, the use of typical metal-based CVD graphene suffers from the residue contamination of polymer transfer-support and heavy metal ions. In this work, we directly grew few-layer graphene on the SiO2/Si substrate without transfer process and then fabricated graphene-based glucose sensors by sequentially immobilizing glucose oxidase and depositing Nafion layer on its surface that was functionalized by oxygen-plasma treatment. Our transfer- and metal-free process shows distinct advantage over the common metal-CVD method in improving the electrochemical performance by eliminating the contamination of transfer-residue. Thus-obtained glucose sensor shows a high sensitivity (16.16 μA mM-1 cm-2) with a detection limit of 124.19 μM. This method is simple and promising for the development of highly sensitive glucose sensors.

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High strength and ductility Mg-8Gd-3Y-0.5Zr alloy with bimodal structure and nano-precipitates
Xiaoxiao Wei, Li Jin, Fenghua Wang, Jing Li, Nan Ye, Zhenyan Zhang, Jie Dong
J. Mater. Sci. Technol.    2020, 44 (0): 19-23.   doi:10.1016/j.jmst.2019.10.024
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To resolve the strength-ductility trade-off problem for high-strength Mg alloys, we prepared a high performance Mg-8Gd-3Y-0.5 Zr (wt%) alloy with yield strength of 371 MPa, ultimate tensile strength of 419 MPa and elongation of 15.8%. The processing route involves extrusion, pre-deformation and aging, which leads to a bimodal structure and nano-precipitates. Back-stress originated from the deformation-incompatibility in the bimodal-structure alloy can improve ductility. In addition, dislocation density in coarse grains increased during the pre-deformation strain of 2%, and the dislocations in coarse grains can promote the formation of chain-like nano-precipitates during aging treatment. The chain-like nano-precipitates can act as barriers for dislocations slip and the existing mobile dislocations enable good ductility.

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Theoretical prediction on thermal and mechanical properties of high entropy (Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)C by deep learning potential
Fu-Zhi Dai, Bo Wen, Yinjie Sun, Huimin Xiang, Yanchun Zhou
J. Mater. Sci. Technol.    2020, 43 (0): 168-174.   doi:10.1016/j.jmst.2020.01.005
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High entropy materials (HEMs, e.g. high entropy alloys, high entropy ceramics) have gained increasing interests due to the possibility that they can provide challenge properties unattainable by traditional materials. Though a large number of HEMs have emerged, there is still in lack of theoretical predictions and simulations on HEMs, which is probably caused by the chemical complexity of HEMs. In this work, we demonstrate that the machine learning potentials developed in recent years can overcome the complexity of HEMs, and serve as powerful theoretical tools to simulate HEMs. A deep learning potential (DLP) for high entropy (Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)C is fitted with the prediction error in energy and force being 9.4 meV/atom and 217 meV/Å, respectively. The reliability and generality of the DLP are affirmed, since it can accurately predict lattice parameters and elastic constants of mono-phase carbides TMC (TM = Ti, Zr, Hf, Nb and Ta). Lattice constants (increase from 4.5707 Å to 4.6727 Å), thermal expansion coefficients (increase from 7.85×10-6 K-1 to 10.58×10-6 K-1), phonon thermal conductivities (decrease from 2.02 W·m-1·K-1 to 0.95 W·m-1·K-1), and elastic properties of high entropy (Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)C in temperature ranging from 0 °C to 2400 °C are predicted by molecular dynamics simulations. The predicted room temperature properties agree well with experimental measurements, indicating the high accuracy of the DLP. With introducing of machine learning potentials, many problems that are intractable by traditional methods can be handled now. It is hopeful that deep insight into HEMs can be obtained in the future by such powerful methods.

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Large electric field-induced strain in the novel BNKTAN-BNBLTZ lead-free ceramics
Chao Wang, Qiang Li, Weiming Zhang, Huiqing Fan
J. Mater. Sci. Technol.    2020, 45 (0): 15-22.   doi:10.1016/j.jmst.2019.09.040
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(1-x)Bi0.5(Na0.82K0.18)0.5Ti0.96(Al0.5Nb0.5)0.04O3-xBi0.46Na0.46Ba0.5La0.02Ti0.97Zr0.03O3 lead-free ceramics (abbreviated as BNKTAN-100xBNBLTZ) was prepared by the conventional solid reaction. XRD patterns and EDS spectrums revealed that a stable solid solution had been formed between BNBLTZ and BNKTAN. With the introduction of BNBLTZ anti-ferroelectric content, BNKTAN relaxor ferroelectrics exhibited the excellent field-induced-strain for x = 0.04 corresponding to electric field-induced strain S ~ 0.505 % and normal strain d33* ~777 pm/V at 65 kV/cm. The large strain response was attributed to the emergence of PNRs in the relaxation process. Additionally, an excellent fatigue resistance performance was obtained within 105 cycles (S = 0.505 %-0.495 % and d33* = 777-758 pm/V, 65 kV/cm). It suggested that prepared ceramics had the great potential to strain sensor and actuators.

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High entropy (Yb0.25Y0.25Lu0.25Er0.25)2SiO5 with strong anisotropy in thermal expansion
Heng Chen, Huimin Xiang, Fu-Zhi Dai, Jiachen Liu, Yanchun Zhou
J. Mater. Sci. Technol.    2020, 36 (0): 134-139.   doi:10.1016/j.jmst.2019.07.022
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A novel high entropy (HE) rare earth monosilicate (Yb0.25Y0.25Lu0.25Er0.25)2SiO5 was synthesized by solid-state reaction method. X-ray diffraction and scanning electron microscopy analysis indicate that a single solid solution is formed with homogeneous distribution of rare-earth elements. HE (Yb0.25Y0.25Lu0.25Er0.25)2SiO5 exhibits excellent phase stability and anisotropy in thermal expansion. The coefficients of thermal expansion (CTEs) in three crystallographic directions are: αa = (2.57 ± 0.07) ×10-6 K-1, αb = (8.07 ± 0.13) ×10-6 K-1, αc = (9.98 ± 0.10) ×10-6 K-1. The strong anisotropy in thermal expansion is favorable in minimizing the coating/substrate mismatch if preferred orientation of HE (Yb0.25Y0.25Lu0.25Er0.25)2SiO5 is controlled on either metal or ceramic substrate.

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New para-magnetic (CoFeNi)50(CrMo)50-x(CB)x (x = 20, 25, 30) non-equiatomic high entropy metallic glasses with wide supercooled liquid region and excellent mechanical properties
Kim Jeong Tae, Hong Sung Hwan, Park Jin Man, Jürgen Eckert, Kim Ki Buem
J. Mater. Sci. Technol.    2020, 43 (0): 135-143.   doi:10.1016/j.jmst.2020.01.004
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In this study, high entropy metallic glasses (HEMGs) were developed through a combination of concepts for designing metallic glasses (main element + transition metal + metalloid element) and high-entropy alloys (more than five elements, each element having an atomic concentration between 5 at.% and 35 at.%). The developed metallic glass alloys are composed of Co-Fe-Ni main elements, transition metals (Cr, Mo) and metalloid elements (C, B). Moreover, the present work reports the thermal, mechanical and magnetic properties of (CoFeNi)50(CrMo)50-x(CB)x alloys with x = 20, 25, 30. The developed as-spun HEMGs exhibit typical paramagnetic properties even for a high amount of ferromagnetic elements (Co, Fe, and Ni) and have high elastic modulus (103-160 GPa) and hardness (14-27 GPa), thus possessing mechanical properties similar to well-known Co-based metallic glasses (Co-Cr-Mo-C-B system). In addition, some of the bulk samples prepared with a diameter of 2 mm form bulk metallic glasses with a high compressive strength around 3.5 GPa. The mechanisms determining the stability of the supercooled liquid, as well as the paramagnetic and mechanical properties for the developed non-equiatomic HEMGs, are discussed.

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Towards understanding twinning behavior near fracture surface in magnesium
Hao Li, Qinghui Zeng, Pengfei Yang, Qi Sun, Jianmin Wang, Jian Tu, Minhao Zhu
J. Mater. Sci. Technol.    2020, 43 (0): 230-237.   doi:10.1016/j.jmst.2020.01.007
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Deformation twin is one of the most important strain accommodation mechanisms and ultimately influences the mechanical properties for magnesium and its alloys. Especially, {10$\bar{1}$1} twin is usually thought to be closely related to the fracture or fatigue process of magnesium alloys. In the present work, the characteristics of microstructure near fracture region of deformed magnesium alloy have been investigated by a combination of electron back-scatter diffraction (EBSD) and transmission electron microscope (TEM). It has found that a large of deformation twins occur near fraction region, including {10$\bar{1}$2} and {10$\bar{1}$1} primary twins, {10$\bar{1}$1}-{10$\bar{1}$2} double twin and {10$\bar{1}$1}-{10$\bar{1}$2}-{10$\bar{1}$1}-{10$\bar{1}$2} quadruple twin. The actual boundaries of {10$\bar{1}$1} twins at atomic scale consist of {10$\bar{1}$1} coherent twinning boundaries (TBs) and parallel basal-pyramidal (BPy/PyB) planes. The tip of {10$\bar{1}$1} twin can even end up with BPy/PyB interfaces only. The experimental observations also reveal that when two {10$\bar{1}$1} twin variants sharing a common [11$\bar{2}$0] zone axis approach each other, the growth of one twin is usually hindered by the boundaries of the other twin. In addition, an apparent “crossing” phenomenon is also discovered when interaction of two {10$\bar{1}$1} twins takes place. According to these experimental observations, the possible underlying mechanisms behind such phenomena are proposed and discussed. These finding are expected to provide an insight into understanding the twinning behavior and the relationship between twin and fracture in magnesium and other materials with hexagonal structure.

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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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Heat transfer and fluid flow and their effects on the solidification microstructure in full-penetration laser welding of aluminum sheet
Shaoning Geng, Ping Jiang, Xinyu Shao, Lingyu Guo, Xuesong Gao
J. Mater. Sci. Technol.    2020, 46 (0): 50-63.   doi:10.1016/j.jmst.2019.10.027
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Understanding the behaviors of heat transfer and fluid flow in weld pool and their effects on the solidification microstructure are significant for performance improvement of laser welds. This paper develops a three-dimensional numerical model to understand the multi-physical processes such as heat transfer, melt convection and solidification behavior in full-penetration laser welding of thin 5083 aluminum sheet. Solidification parameters including temperature gradient G and solidification rate R, and their combined forms are evaluated to interpret solidification microstructure. The predicted weld dimensions and the microstructure morphology and scale agree well with experiments. Results indicate that heat conduction is the dominant mechanism of heat transfer in weld pool, and melt convection plays a critical role in microstructure scale. The mushy zone shape/size and solidification parameters can be modulated by changing process parameters. Dendritic structures form because of the low G/R value. The scale of dendritic structures can be reduced by increasing GR via decreasing heat input. The columnar to equiaxed transition is predicted quantitatively via the process related G3/R. These findings illustrate how heat transfer and fluid flow affect the solidification parameters and hence the microstructure, and show how to improve microstructure by optimizing the process.

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