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CN 21-1315/TG
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Current Issue
 20 July 2019, Volume 35 Issue 7 Previous Issue    Next Issue
Orginal Article
 Select Microstructure, mechanical properties and deformation mechanisms of an as-cast Mg-Zn-Y-Nd-Zr alloy for stent applications Jianfeng Wang, Hongbo Zhou, Liguo Wang, Shijie Zhu, Shaokang Guan J. Mater. Sci. Technol., 2019, 35 (7): 1211-1217.  DOI: 10.1016/j.jmst.2019.01.007 A new Mg-2Zn-0.2Y-0.5Nd-0.4 Zr (wt%) alloy designed specially for stent applications has been developed. The as-cast alloy is featured with equiaxed grains with a mean size of about 40 μm and a small amount of second phase (T phase) distributed discontinuously either at the grain boundaries or inside the grains. This alloy exhibits a tensile elongation of up to 35%, which is much larger than that of most reported other as-cast Mg alloys. The tensile deformation mechanisms have also been investigated. The results show that, besides basal slip, {10 - 12} extension twining and non-basal pyramidal slips can also be observed at initial stage and later stage during tensile deformation, respectively, which are responsible for the good room-temperature ductility.
 Select Optimizing the low-pressure carburizing process of 16Cr3NiWMoVNbE gear steel Haojie Wang, Bin Wang, Zhaodong Wang, Yong Tian, R.D.K. Misra J. Mater. Sci. Technol., 2019, 35 (7): 1218-1227.  DOI: 10.1016/j.jmst.2019.02.001 Compared with the traditional atmospheric carburization, low-pressure carburization has the benefits of producing no surface oxidation and leaving fine, uniformly dispersed carbides in the carburized layer. However, the process parameters for low-pressure carburization of 16Cr3NiWMoVNbE steel have yet to be optimized. Thus, we use the saturation-value method to optimize these parameters for aviation-gear materials. Toward this end, the microstructure and properties of 16Cr3NiWMoVNbE steel after different carburization processes are studied by optical microscopy, scanning electron microscopy, transmission electron microscopy, and electron probe microanalysis. Considering the saturated austenite carbon concentration, we propose a model of carbon flux and an alloy coefficient for low-pressure carburization to reduce the carbon concentration in austenite and avoid the surface carbide network. At the early stage of carburization ($\widetilde{3}$0 s), the gas-solid interface has a higher concentration gradient. The averaging method is not ideal in practical applications, but the carbon flux measured by using the segmented average method is 2.5 times that measured by the overall average method, which is ideal in practical applications. The corresponding carburization time is reduced by 60%. By using the integral average method, the actual carburization time increases, which leads to the rapid formation of carbide on the surface and affects the entire carburization process. Nb and W combine with C to form carbides, which hinders carbon diffusion and consumes carbon, resulting in a sharp decrease in the rate of C diffusion in austenite (the diffusion rate is reduced by $\widetilde{5}$2% for 16Cr3NiWMoVNbE steel). By changing the diffusion coefficient model and comparing the hardness gradient of different processes, the depth of the actual layer is found to be very similar to the design depth.
 Select Effect of tin addition on corrosion behavior of a low-alloy steel in simulated costal-industrial atmosphere Bo Liu, Xin Mu, Ying Yang, Long Hao, Xueyong Ding, Junhua Dong, Zhe Zhang, Huaxing Hou, Wei Ke J. Mater. Sci. Technol., 2019, 35 (7): 1228-1239.  DOI: 10.1016/j.jmst.2019.01.008 The effect of tin addition on the atmospheric corrosion behavior of a low-alloy steel in simulated coastal-industrial atmosphere has been investigated by indoor wet/dry cyclic corrosion test (CCT). The results indicate that tin addition can obviously make the steel substrate more resistant to atmospheric corrosion by suppressing the cathodic H+ reduction reaction, and but tin addition is not of obvious beneficial effect when the steel is covered with a thicker rust layer during long-term corrosion process. The reason lies in the fact that the presence of un-reduced H+ can lower the electrolyte pH value and lead to a loose and porous rust layer on tin-containing steel sample than that on tin-free steel sample. In addition, the 120 CCT cycles corrosion process of the two steels can be divided into three stages. Both the tin-free and tin-containing steels show an increasing corrosion rate during the initial corrosion stage and then exhibit a decreasing corrosion rate during the second and third corrosion stages. Moreover, tin addition makes the tin-containing steel rust layer have a higher amount of α-FeOOH and lower amount of γ-FeOOH and Fe3O4 than the tin-free steel rust layer.
 Select Effect of tempering temperature on the microstructure and properties of ultrahigh-strength stainless steel Yangpeng Zhang, Dongping Zhan, Xiwei Qi, Zhouhua Jiang J. Mater. Sci. Technol., 2019, 35 (7): 1240-1249.  DOI: 10.1016/j.jmst.2019.01.009 The microstructure, precipitation and mechanical properties of Ferrium S53 steel, a secondary hardening ultrahigh-strength stainless steel with 10% Cr developed by QuesTek Innovations LLC, upon tempering were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and tensile and impact tests. Based on these results, the influence of the tempering temperature on the microstructure and properties was discussed. The results show that decomposition occurred when the retained austenite was tempered above 440 °C and that the hardening peak at 482 °C was caused by the joint strengthening of the precipitates and martensite transformation. Due to the high Cr content, the trigonal M7C3 carbide precipitated when the steel was tempered at 400 °C, and M7C3 and M2C (5-10 nm in size) coexisted when it was tempered at 482 °C. When the steel was tempered at 630 °C, M2C and M23C6 carbides precipitated, and the sizes were greater than 50 nm and 500 nm, respectively, but no M7C3 carbide formed. When the tempering temperature was above 540 °C, austenitization and large-size precipitates were the main factors affecting the strength and toughness.
 Select Triple effects of Sn-substitution on Na0.67Ni0.33Mn0.67O2 Xiaohui Rong, Fei Gao, Feixiang Ding, Yaxiang Lu, Kai Yang, Hong Li, Xuejie Huang, Liquan Chen, Yong-Sheng Hu J. Mater. Sci. Technol., 2019, 35 (7): 1250-1254.  DOI: 10.1016/j.jmst.2019.01.010 Layered oxides are one of the most promising cathode materials for sodium ion batteries (NIBs), however, the relatively low working voltage hinders the increase of energy density thus limiting the application scenarios of NIBs. Here we prepared and investigated a series of Sn4+ substituted Na0.67Ni0.33Mn0.67-xSnxO2 (x = 0.10, 0.20, 0.30, 0.33) and found that Sn-substitution can induce three effects: promoting O3-stack formation, smoothing the voltage profile and increasing the working voltage to ～3.6 V. This study would enrich the knowledge of Sn-substitution and give guide to the better design of high-voltage cathode materials for NIBs.
 Select Preparation and properties of a new porous ceramic material used in clean energy field Shuming Wang, Xiaofang Zhang, Fenghua Kuang, Jiangshan Li, Yanxin Wang, Ruiping Wang, Yanru Wang, Xin Lin, Jianming Li J. Mater. Sci. Technol., 2019, 35 (7): 1255-1260.  DOI: 10.1016/j.jmst.2019.03.038 At high temperature, the oxide redox reactions of ceria can split H2O and CO2 to produce H2 and CO, so porous ceria with high temperature resistance and high specific surface area has an important foreground in clean energy applications. In this work, a reticulated porous ceria ceramic material with interconnected porous structure was prepared by the impregnation technique using organic polyurethane sponges as template. The influences of pretreated sponge, dipping time length, pore size and sintering temperature on the porosity and strength of the porous ceria ceramics were systematically studied. With the increasing sintering temperature, the glass phase occurred and led to an increase in strength, but an decrease in porosity. Eventually, we analyzed the relationships between porosity and strength of these porous materials, aiming to provide theoretical and practical references for its application in clean-energy field.
 Select Joint formation mechanism of high depth-to-width ratio friction stir welding Yongxian Huang, Yuming Xie, Xiangchen Meng, Junchen Li, Li Zhou J. Mater. Sci. Technol., 2019, 35 (7): 1261-1269.  DOI: 10.1016/j.jmst.2019.01.016 High depth-to-width ratio friction stir welding is an attractive method for the joining demands of aluminum profiles, which is sparked with its extremely low heat input and high mechanical performance. In this study, the joint formation mechanism was studied by a numerical model of plastic flow combined with experimental approaches. A fluid-solid-interaction algorithm was proposed to establish the coupling model, and the material to be welded was treated as non-Newtonian fluid. The thread structure and the milling facets on tool pin promoted drastic turbulence of material. The thread structure converged the plasticized material by its inclined plane, and then drove the attached material to refill the welds. The milling facets brought about the periodic dynamic material flow. The thread structure and the milling facets increased the strain rate greatly under the extremely low heat input, which avoided the welding defects. The condition of the peak temperature of 648 K and the strain rate of 151 s-1 attributed to the lowest coarsening degree of precipitate. The tensile strength of the joint reached 265 MPa, equivalent to 86% of base material. The amelioration via the material flow model inhibits the welding defects and optimizes the parameter intervals, providing references to extracting process-structure-property linkages for friction stir welding.
 Select Stress rupture properties and deformation mechanisms of K4750 alloy at the range of 650 °C to 800 °C Meiqiong Ou, Yingche Ma, Weiwei Xing, Xianchao Hao, Bo Chen, Leilei Ding, Kui Liu J. Mater. Sci. Technol., 2019, 35 (7): 1270-1277.  DOI: 10.1016/j.jmst.2019.03.002 The stress rupture properties and deformation mechanisms of K4750 alloy at 650 °C, 700 °C, 750 °C and 800 °C were investigated. As the decrease of temperature and stress, the stress rupture life gradually increased. A Larson-Miller Parameter (LMP) method was used for analyzing the stress rupture life under different conditions. The linear fitting formula between stress (σ) and LMP was derived as σ = 3166.455 - 119.969 × LMP and the fitting coefficient was 0.98. After testing, the dislocation configurations of all stress rupture samples were investigated by transmission electron microscopy (TEM). The temperature and stress had a significant impact on the deformation mechanism, thereby affected the stress rupture life of K4750 alloy. As the increasing stress at a given temperature, the deformation mechanism gradually transformed from Orowan looping to stacking fault shearing. Based on experimental results, the threshold stress at 650 °C, 700 °C, 750 °C and 800 °C for the transition of deformation mechanism was estimated to be about 650 MPa, 530 MPa, 430 MPa and 350 MPa, respectively. Below the threshold stress, γ' phase effectively hindered dislocation motion by Orowan looping mechanism, K4750 alloy had a long stress rupture life. Slightly above the threshold stress, Orowan looping combining stacking fault shearing was the dominant mechanism, the stress rupture life decreased. As the further increase of stress, stacking fault shearing acted as the dominant deformation mechanism, the resistance to dislocation motion decreased rapidly, so the stress rupture life reduced significantly.
 Select Effect of heat-input on pitting corrosion behavior of friction stir welded high nitrogen stainless steel H. Zhang, P. Xue, D. Wang, L.H. Wu, D.R. Ni, B.L. Xiao, Z.Y. Ma J. Mater. Sci. Technol., 2019, 35 (7): 1278-1283.  DOI: 10.1016/j.jmst.2019.01.011 In this study, different welding parameters were selected to investigate the effects of heat-input on the microstructure and corrosion resistance of the friction stir welded high nitrogen stainless steel joints. The results showed that, the welding speed had major influence on the duration at elevated temperature rather than the peak temperature. The hardness distribution and tensile properties of the nugget zones (NZs) for various joints were very similar while the pitting corrosion behavior of various NZs showed major differences. Large heat-input resulted in the ferrite bands being the pitting location, while tool wear bands were sensitive to pitting corrosion in the low heat-input joints. Cr diffusion and tool wear were the main reasons for pitting. The mechanisms of pitting corrosion in the NZs were analyzed in detail.
 Select Trabecular-like Ti-6Al-4V scaffolds for orthopedic: fabrication by selective laser melting and in vitro biocompatibility Huixin Liang, Youwen Yang, Deqiao Xie, Lan Li, Ning Mao, Changjiang Wang, Zongjun Tian, Qing Jiang, Lida Shen J. Mater. Sci. Technol., 2019, 35 (7): 1284-1297.  DOI: 10.1016/j.jmst.2019.01.012 Porous metal scaffolds play an important role in the orthopedic field, due to their wide applications in prostheses implantation. Some previous studies showed that the scaffolds with trabecular bone structure reconstructed via computed tomography had satisfactory biocompatibility. However, the reverse modeling scaffolds were inflexible for customized design. Therefore, a top-down designing biomimetic bone scaffold with favorable mechanical performances and cytocompatibility is urgently demanded for orthopedic implants. An emerging additive manufacturing technique, selective laser melting, was employed to fabricate the trabecular-like porous Ti-6Al-4 V scaffolds with varying irregularities (0.05-0.5) and porosities (48.83%-74.28%) designed through a novel Voronoi-Tessellation based method. Micro-computed tomography and scanning electron microscopy were used to characterize the scaffolds’ morphology. Quasi-static compression tests were performed to evaluate the scaffolds’ mechanical properties. The MG63 cells culture in vitro experiments, including adhesion, proliferation, and differentiation, were conducted to study the cytocompatibility of scaffolds. Compressive tests of scaffolds revealed an apparent elastic modulus range of 1.93-5.24 GPa and an ultimate strength ranging within 44.9-237.5 MPa, which were influenced by irregularity and porosity, and improved by heat treatment. Furthermore, the in vitro assay suggested that the original surface of the SLM-fabricated scaffolds was favorable for osteoblasts adhesion and migration because of micro scale pores and ravines. The trabecular-like porous scaffolds with full irregularity and higher porosity exhibited enhanced cells proliferation and osteoblast differentiation at earlier time, due to their preferable combination of small and large pores with various shapes. This study suggested that selective laser melting-derived Ti-6Al-4 V scaffold with the trabecular-like porous structure designed through Voronoi-Tessellation method, favorable mechanical performance, and good cytocompatibility was a potential biomaterial for orthopedic implants.
 Select Effects of rare earth elements on inclusions and impact toughness of high-carbon chromium bearing steel Chaoyun Yang, Yikun Luan, Dianzhong Li, Yiyi Li J. Mater. Sci. Technol., 2019, 35 (7): 1298-1308.  DOI: 10.1016/j.jmst.2019.01.015 High-carbon chromium bearing steels with different rare earth (RE) contents were prepared to investigate the effects of RE on inclusions and impact toughness by different techniques. The results showed that RE addition could modify irregular Al2O3 and MnS into regular RE inclusions. With the increase of RE content, the reaction sequence of RE and potential inclusion forming elements should be O, S, As, P and C successively. RE inclusions containing C might precipitate in molten steel and solid state, but the precipitation temperature was significantly higher than that of carbides in high-carbon chromium bearing steel. For experimental bearing steels, the volume fraction of inclusions increased steadily with the increase of RE content, but smaller and more dispersed inclusions could be obtained by 0.018% RE content compared with bearing steel without RE, whereas the continuous increase of RE content led to an increasing trend for inclusion size and a gradual deterioration for inclusion distribution. RE addition could improve the transverse impact toughness and isotropy of bearing steel, and for modified high-carbon chromium bearing steel by RE alloying, the increase of RE content continuously increased both transverse and longitudinal impact toughness until excessive RE addition.
 Select Probing the degenerate pattern growth of {100}<011> orientation in a directionally solidified Al-4.5 wt% Cu alloy Yumin Wang, Shuangming Li, Zhenpeng Liu, Hong Zhong, Lei Xu, Hui Xing J. Mater. Sci. Technol., 2019, 35 (7): 1309-1314.  DOI: 10.1016/j.jmst.2019.03.004 Degenerate pattern is a seemingly disordered morphology but it exhibits the inherently ordered crystal connected with tip-splitting and limited stability which makes it difficult to observe in the metallic system. Here we employ (100)[011] orientated planar-front seeds using directional solidification and reveal the fundamental origins of the degenerate pattern growth in an Al-4.5 wt% Cu alloy. We find that the spacing of the tip-splitting (λ) in the degenerate of the alloys followed a power law, λ∝V-0.5, and the frequency (f) of the splitting was related to the growth velocity (V) by f∝V1.5. The dimensionless growth direction (θ/θ0) increased monotonously and approached 0.6 with faster velocity, attributed to its anisotropy in the interface kinetics. Once growth velocity exceeded a threshold, two types of pattern transitions from degenerate to regular dendrites were proposed. One of them exhibited a random and chaotic mode and the other underwent a rotation in growth direction.
 Select The effects of fabrication atmosphere condition on the microstructural and mechanical properties of laser direct manufactured stainless steel 17-4 PH D. Wang, C.T. Chi, W.Q. Wang, Y.L. Li, M.S. Wang, X.G. Chen, Z.H. Chen, X.P. Cheng, Y.J. Xie J. Mater. Sci. Technol., 2019, 35 (7): 1315-1322.  DOI: 10.1016/j.jmst.2019.03.009 The effects of atmosphere conditions on microstructural and mechanical properties of stainless steel 17-4PH components fabricated by laser direct manufacturing (LDM) were investigated through measurements on phase constitution, porosity, tensile strength, fracture morphology, hardness and evolution of substrate temperature. Results showed that the samples produced in air atmosphere condition possessed higher tensile strength and hardness for both as-deposited and heat-treated states than that in Ar chamber condition, due to dispersion strengthening effect of amorphous oxide particles and nitrogen solution strengthening as a result of higher content of oxygen and nitrogen. The temperature of substrate heat accumulation was higher in Ar chamber condition, leading to dramatically lower porosity and more reverse austenite, which also contributed to the lower strength and hardness.
 Select Mechanical, forming and biological properties of Ti-Fe-Zr-Y alloys prepared by 3D printing Liying Han, Cunshan Wang, Zhengwei Li J. Mater. Sci. Technol., 2019, 35 (7): 1323-1333.  DOI: 10.1016/j.jmst.2019.01.003 Biomedical Ti-Fe-Zr-Y alloys were prepared by 3D printing on pure titanium substrate. The influences of Zr on mechanical, forming, and biological properties of the alloys were investigated in detail. The results showed that with increasing the Zr addition, the surface roughness, friction coefficient and worn volume decrease at first and then increase, the lowest values obtained at 5.86 at.% Zr addition. The ultimate compression stress and specific strength gradually decrease. The studied alloys have no cytotoxicity. They can promote the early adhesion and proliferation of cells. The eutectic alloy with 5.86 at.% Zr addition has the best ability of apatite deposition, it exhibits a better comprehensive performance among the studied alloys, which is superior to the Ti70.5Fe29.5 and Ti-6Al-4 V alloys.
 Select Benefits of Zr addition to oxidation resistance of a single-phase (Ni,Pt)Al coating at 1373 K Chengyang Jiang, Lingyi Qian, Min Feng, He Liu, Zebin Bao, Minghui Chen, Shenglong Zhu, Fuhui Wang J. Mater. Sci. Technol., 2019, 35 (7): 1334-1344.  DOI: 10.1016/j.jmst.2019.03.013 A single-phase (Ni,Pt)Al coating with lean addition of Zr was prepared by co-electroplating of Pt-Zr composite plating and subsequent gaseous aluminization treatments. Isothermal and cyclic oxidation behavior of the Zr-doped (Ni,Pt)Al coating samples was assessed at 1373 K in static air in comparison with plain nickel aluminide (NiAl) and normal (Ni,Pt)Al coatings. Results indicated that Zr-doped (Ni,Pt)Al coating demonstrated a lower oxidation rate constant and reduced tendency of oxide scale spallation as well as surface rumpling, in which the enhanced oxidation performance was mainly attributed to the segregation of Zr at oxide scale grain boundaries and the improved Young’s modulus of the coating. Besides, the addition of Zr effectively delayed oxide phase transformation of Al2O3 from θ phase to α phase in the early oxidation stage and coating degradation of β-NiAl to γ'-Ni3Al in the stable oxidation stage.
 Select The improved mechanical properties of Al matrix composites reinforced with oriented β-Si3N4 whisker Chenxu Zhanga, Yu-Ping Zeng, Dongxu Yao, Jinwei Yin, Kaihui Zuo, Yongfeng Xia, Hanqin Liang J. Mater. Sci. Technol., 2019, 35 (7): 1345-1353.  DOI: 10.1016/j.jmst.2019.02.003 The β-Si3N4 whiskers (β-Si3N4w) reinforced Al matrix composites were first fabricated by hot pressing, then treated through hot extrusion. The microstructure characterization demonstrated the preferred orientations of both β-Si3N4w and Al grains in the as-extruded composites. It indicated that β-Si3N4w were aligned along the extrusion direction and Al grains exhibited a distinct <111>Al texture. The interface between β-Si3N4w and Al was in a good bonding status without voids and reaction products. Effects of extrusion process on the mechanical properties of composites were also investigated. The results indicated the extrusion process had a prominent strengthening effect on the mechanical properties of composites. The maximum yield strength and ultimate tensile strength of composites reached up to 170 and 289 MPa, respectively, accompanied by a 12.3% elongation at fracture when the whisker fraction was 15 vol.%. This improvement was collectively attributed to the densification of composites, the strong interface, and the preferred orientation inside composites. The yield strength of the composites reinforced with 5 vol.% β-Si3N4w corresponded well with the theoretical value from different strengthening mechanisms.
 Select Grain size-dependent Mg/Si ratio effect on the microstructure and mechanical/electrical properties of Al-Mg-Si-Sc alloys Shengyu Jiang, Ruihong Wang J. Mater. Sci. Technol., 2019, 35 (7): 1354-1363.  DOI: 10.1016/j.jmst.2019.03.011 Al-Mg-Si-Sc alloys with different Mg/Si ratio (<1.73 in wt.% vs>1.73 in wt.%) and different grain size (coarse grains vs ultrafine grains) were prepared, which allowed to investigate the grain size-dependent Mg/Si ratio effect on the microstructural evolution and concomitantly on the hardness and electrical conductivity when subjected to aging at 200 °C. In the coarse-grained Al-Mg-Sc-Sc alloys, the β″ precipitation within the grain interior and also the precipitation hardening were highly dependent on the Mg/Si ratio, while the electrical conductivity was slightly affected by the Mg/Si ratio. A promoted β″ precipitation was found in the case of Si excess (Mg/Si ratio <1.73), much greater than in the case of Mg excess (Mg/Si ratio>1.73). While in the ultrafine-grained Al-Mg-Si-Sc alloys, the electrical conductivity rather than the hardness was more sensitive to the Mg/Si ratio. The alloy with Si excess displayed electrical conductivity much higher than its counterpart with Mg excess. This is rationalized by the grain boundary precipitation promoted by Si, which reduced the solute atoms and precipitates within the grain interior. Age softening was found in the ultrafine-grained alloy with Si excess, but the ultrafine-grained alloy with Mg excess held the hardness almost unchanged during the aging. The hardness-conductivity correlation is comprehensively discussed by considering the coupling effect of Mg/Si ratio and grain size. A strategy to simultaneously increase the hardness/strength and electrical conductivity is proposed for the Al-Mg-Si-Sc alloys, based on present understanding of the predominant factors on strengthening and conductivity, respectively.
 Select Storage and transfer of optical excitation energy in GaInP epilayer: Photoluminescence signatures Shijie Xu, Ying Huang, Zhicheng Su, Rongxin Wang, Jianrong Dong, Deliang Zhu J. Mater. Sci. Technol., 2019, 35 (7): 1364-1367.  DOI: 10.1016/j.jmst.2019.03.010 GaInP alloy could be the most trusted key material for fabricating super-high-efficiency single- and multi-junction solar cells, especially for space applications. The storage and transfer of optical excitation energy in this key alloy is thus a key subject of the energy conversion from optical to electrical. In this article we present a study of the subject through investigating photoluminescence (PL) degradation in the GaInP epilayer at 4 K under the continuous optical excitations of ultraviolet (UV) 325 nm, visible 488.0 and 514.5 nm lasers. It is found that the decline of PL intensity with the irradiation time may be represented by I(t)/I0=(1+tτ-1)-1+C, where I0 is the luminescence intensity at the beginning of irradiation, τ a time constant, and C a background. Moreover, the PL degradation degree reduces with increasing the excitation wavelength. In addition, some red shift of the PL peak is observed accompanying with the intensity decline under the UV laser excitation. These PL signatures indicate that the localized carriers within the local atomic ordering domains play a major role in the storage and transfer of the excitation energy via photon recycling processes.
 Select Effects of samarium content on microstructure and mechanical properties of Mg-0.5Zn-0.5Zr alloy Kai Guan, Fanzhi Meng, Pengfei Qin, Qiang Yang, Dongdong Zhang, Baishun Li, Wei Sun, Shuhui Lv, Yuanding Huang, Norbert Hort, Jian Meng J. Mater. Sci. Technol., 2019, 35 (7): 1368-1377.  DOI: 10.1016/j.jmst.2019.01.019 Effects of samarium (Sm) content (0, 2.0, 3.5, 5.0, 6.5 wt%) on microstructure and mechanical properties of Mg-0.5Zn-0.5 Zr alloy under as-cast and as-extruded states were thoroughly investigated. Results indicate that grains of the as-cast alloys are gradually refined as Sm content increases. The dominant intermetallic phase changes from Mg3Sm to Mg41Sm5 till Sm content exceeds 5.0 wt%. The dynamically precipitated intermetallic phase during hot-extrusion in all Sm-containing alloys is Mg3Sm. The intermetallic particles induced by Sm addition could act as heterogeneous nucleation sites for dynamic recrystallization during hot extrusion. They promoted dynamic recrystallization via the particle stimulated nucleation mechanism, and resulted in weakening the basal texture in the as-extruded alloys. Sm addition can significantly enhance the strength of the as-extruded Mg-0.5Zn-0.5 Zr alloy at room temperature, with the optimal dosage of 3.5 wt%. The optimal yield strength (YS) and ultimate tensile strength (UTS) are 368 MPa and 383 MPa, which were enhanced by approximately 23.1% and 20.8% compared with the Sm-free alloy, respectively. Based on microstructural analysis, the dominant strengthening mechanisms are revealed to be grain boundary strengthening and dispersion strengthening.
 Select Influence of cerium content on the corrosion behavior of Al-Co-Ce amorphous alloys in 0.6 M NaCl solution L.M. Zhang, S.D. Zhang, A.L. Ma, A.J. Umoh, H.X. Hu, Y.G. Zheng, B.J. Yang, J.Q. Wang J. Mater. Sci. Technol., 2019, 35 (7): 1378-1387.  DOI: 10.1016/j.jmst.2019.03.014 The effect of cerium content on the corrosion behavior of Al-Co-Ce amorphous alloys in 0.6 M NaCl solution was investigated by cyclic polarization, Mott-Schottky and X-ray photoelectron spectroscopy techniques. Results indicated that the open circuit potential of Al-Co-Ce amorphous alloys displayed a decreased tendency with the increase in Ce content, and the amorphous alloy with 4 at.% Ce presented both the lowest passive current density and donor density indicating the best corrosion resistance, while adding excess Ce led to the reduced corrosion resistance of Al-Co-Ce alloys. Furthermore, it was found that a low Ce content is beneficial to the formation of a more protective passive film on Al-Co-Ce amorphous alloys, and the corrosion inhibition reactions of Al-Co-Ce alloys in 0.6 M NaCl solution were changed with the increase in Ce content and the detailed reasons were discussed.
 Select In-situ study on hydrogen bubble evolution in the liquid Al/solid Ni interconnection by synchrotron radiation X-ray radiography Zongye Ding, Qiaodan Hu, Wenquan Lu, Xuan Ge, Sheng Cao, Siyu Sun, Tianxing Yang, Mingxu Xia, Jianguo Li J. Mater. Sci. Technol., 2019, 35 (7): 1388-1392.  DOI: 10.1016/j.jmst.2019.03.007 Synchrotron X-ray radiography was used to carry out an in-situ observation of the hydrogen bubble evolution in the liquid Al/solid Ni interconnection. The individual bubble mainly grows in a stochastic way during heating. The size distribution for groups of bubbles follows a Gaussian distribution in the early stage and Lifshitz-Slyozov-Wagner (LSW) diffusion controlled distribution in the final stage. The intermetallic compounds (IMCs) first form during solidification, following by the hydrogen bubbles. The bubbles between two adjacent Al3Ni grains grow unidirectionally along the liquid channel, with the bottom being impeded by the Al3Ni phase and the radius of the growth front being smaller. For the bubbles at triple junctions, they grow along the liquid channel and the crack with morphology transition.
 Select Predicting the degradation behavior of magnesium alloys with a diffusion-based theoretical model and in vitro corrosion testing Zhenquan Shen, Ming Zhao, Dong Bian, Danni Shen, Xiaochen Zhou, Jianing Liu, Yang Liu, Hui Guo, Yufeng Zheng J. Mater. Sci. Technol., 2019, 35 (7): 1393-1402.  DOI: 10.1016/j.jmst.2019.02.004 Magnesium alloys have shown great potential for their use in the medical device field, due to the promising biodegradability. However, it remains a challenge to characterize the degradation behavior of the Mg alloys in a quantitative manner. As such, controlling the degradation rate of the Mg alloys as per our needs is still hard, which greatly limits the practical application of the Mg alloys as a degradable biomaterial. This paper discussed a numerical model developed based on the diffusion theory, which can capture the experimental degradation behavior of the Mg alloys precisely. The numerical model is then implemented into a finite element scheme, where the model is calibrated with the data from our previous studies on the corrosion of the as-cast Mg-1Ca and the as-rolled Mg-3Ge binary alloys. The degradation behavior of a pin implant is predicted using the calibrated model to demonstrate the model’s capability. A standard flow is provided in a practical framework for obtaining the degradation behavior of any biomedical Mg alloys. This methodology was further verified via the comparison with enormous available experimental results. Lastly, the material parameters defined in this model were provided as a new kind of material property.
 Select Formation mechanism of large grains inside annealed microstructure of GH4169 superalloy by cellular automation method Ming-Song Chen, Zong-Huai Zou, Y.C. Lin, Hong-Bin Li, Guan-Qiang Wang J. Mater. Sci. Technol., 2019, 35 (7): 1403-1411.  DOI: 10.1016/j.jmst.2018.11.026 In authors’ previous work [Mater. Charact. 141 (2018) 212-222], it was found that the heterogeneous deformed microstructures can be replaced by the relatively homogeneous recrystallized grains through an annealing treatment. However, there are still some relatively large recrystallized grains. To find the reasons for the formation of large grains, some new annealing treatment tests were done, and the cellular automation (CA) simulations were carried out in the present work. The experimental results showed that the microstructural evolution during annealing treatment is significantly affected by the content of δ phase. So, the effects of δ phase on the nucleation and growth of grains are carefully considered in the CA model to accurately simulate the microstructural evolution behavior. By the CA simulation, it is found that the dislocation density rapidly decreases due to the nucleation of static recrystallization (SRX) and the growth of dynamc recrystallization (DRX) nuclei at the early stage of annealing. The high initial dislocation density can provide the high velocity for the growth of DRX nuclei, which is responsible for the formation of coarse grains. However, the growth rate of SRX nuclei is relatively small due to the low dislocation density and pinning effects of δ phase.
 Select Evaluation of dynamic development of grain structure during friction stir welding of pure copper using a quasi in situ method X.C. Liu, Y.F. Sun, T. Nagira, K. Ushioda, H. Fujii J. Mater. Sci. Technol., 2019, 35 (7): 1412-1421.  DOI: 10.1016/j.jmst.2019.01.018 By employing a quasi in situ method, we investigated the dynamic evolution of the grain structure considering the material flow, strain, and strain rate in the friction stir welding of pure copper. The tool ‘stop action’ and rapid cooling were employed and a brass foil was used as a marker to show the material flow path. The grain structure along the material flow path was characterised using electron backscatter diffraction. Static recrystallization occurs for the work-hardened base material in the preheating stage in front of the tool. In the acceleration flow stage, grains are significantly refined by plastic deformation, discontinuous dynamic recrystallization, annealing twinning during the strain-induced boundary migration and slight continuous dynamic recrystallization. In the deceleration flow stage, due to a strain reversal, the grain first coarsens, and is thereafter refined again. Finally, the hot-deformed material in the shoulder-affected zone is ‘frozen’ directly whereas that in the probe-affected zone undergoes significant annealing; thus, the recrystallized microstructure and 45°-rotated cube texture are obtained in the probe-affected zone.
 Select Segregation behaviors of Sc and unique primary Al3Sc in Al-Sc alloys prepared by molten salt electrolysis Xuan Liu, Jilai Xue, Zhichao Guo, Cheng Zhang J. Mater. Sci. Technol., 2019, 35 (7): 1422-1431.  DOI: 10.1016/j.jmst.2019.02.002 This work mainly deals with the segregating behaviors of Sc and the growth of unique primary Al3Sc in Al-Sc alloys prepared by molten salt electrolysis. The alloys contain 0.23-1.38 wt%Sc where Sc segregation is observed. It is found that a high current density and long electrolysis time are in favor of high Sc content, and so do the high temperature and the addition level of Sc2O3. Sc content at the edge of Al based alloy (average Sc content: 0.75 wt%) can be as high as 1.09 wt%, while it is merely 0.24 wt% at the central area. The cooling rates have a strong impact on the morphology and particle size of primary Al3Sc, but a weak influence on Sc segregation. The cusped cubic and dendritic primary Al3Sc can precipitate in the prepared Al-Sc alloys. In a slightly hypereutectic Al-0.67 wt%Sc alloy, a large and cusped dendrite grows from the edge into the center. The primary and secondary dendritic arms can be as long as 600 and 250 μm, respectively. The Sc segregating behaviors in Al-Sc alloys is due to the mechanism controlled by the limited diffusion rate of Sc in liquid Al. This can involve the establishment of a near spherical discharge interface between liquid Al and the electrolyte. The Sc rich layer near Al-molten salt interface may provide the potential primary nuclei and sufficient Sc atoms for the growth of large dendritic primary Al3Sc.
 Select M2M'AlB4 (M = Mn, Fe, Co, M' = Cr, Mo, W): Theoretical predicted ordered MAB phases with Cr3AlB4 crystal structure Fu-Zhi Dai, Huimin Xiang, Yinjie Sun, Yanchun Zhou J. Mater. Sci. Technol., 2019, 35 (7): 1432-1438.  DOI: 10.1016/j.jmst.2019.03.005 The nanolaminated MAB phases have attracted great research interests due to their unusual combination of metal-like and ceramic-like properties, which is similar to MAX phases. Recently, ordered quaternary MAX phases have been discovered, which enriches the family of MAX phases, and opens a new window to tailor the properties of MAX phases and to develop new MXenes. In the present work, we explored possible ordered quaternary MAB phases with Cr3AlB4 structure (space group: Pmmm) by first-principles calculations. The predictions show that M2M'AlB4 phases with M = Mn, Fe, Co and M' = Cr, Mo, W exhibit strong tendency of ordering, where M locates at 2t site (0.5, 0.5, z2t) and M' locates at 1g site (0, 0.5, 0.5). The main driving force of ordering may be the differences in bonding strengths between Al and M elements. Analyses on chemical bonds reveal that bonding strengths increase following the order: Al-Mn < Al-Fe < Al-Co, which is consistent with the prediction that ordering tendency increases when M changes from Mn to Co, as derived from enthalpy differences. The ordered M2M'AlB4 phases with M = Mn or Fe are predicted ferromagnetic and ordered M2M'AlB4 phases display lower shear resistance and possibly better ductility in comparison to Cr3AlB4.
 Select Plastic anisotropy calculation of severely-deformed Al-Mg-Si alloy considering texture changes in electron backscatter diffraction I Putu Widiantara, Hae Woong Yang, Min Jun Kim, Young Gun Ko J. Mater. Sci. Technol., 2019, 35 (7): 1439-1443.  DOI: 10.1016/j.jmst.2019.03.022 The investigation studied the plastic anisotropy of the severely-deformed Al-Mg-Si alloy by considering texture changes. The sample deformed via asymmetrical rolling under cross-shear condition was annealed at 598 K where recrystallization was in progress. It is found upon annealing that the intensity of Cube ({001}〈100〉) was comparable to those of plane-strain components while the intensities of shear components remained constant despite their instabilities in the recrystallization regime. After annealing, the average Lankford value ($\bar{r}$) of the present sample was close to a unity whereas the in-plane anisotropy (Δr) decreased, resulting in nearly isotropic characteristics of Al-Mg-Si alloy.
 Select Understanding the galvanic corrosion of the Q-phase/Al couple using SVET and SIET Alexander I. Ikeuba, Bo Zhang, Jianqiu Wang, En-Hou Han, Wei Ke J. Mater. Sci. Technol., 2019, 35 (7): 1444-1454.  DOI: 10.1016/j.jmst.2019.03.001 The galvanic corrosion of the Q-phase/Al couple in 0.1 M NaCl solutions has been studied using the scanning vibrating electrode technique (SVET), the scanning ion-selective electrode technique (SIET) and energy dispersive X-ray spectroscopy (EDX). The galvanic corrosion of the Q-phase/Al couple was found to be dependent on pH and immersion time. Current density maps obtained by SVET shows that the anodic oxidation processes emerge from Al in a localized manner in pH 2 and 6 solutions but is initiated in a uniform manner in pH 13 solution, whereas, the cathodic processes are more homogeneously distributed over the Q-phase at pH 2, 6 and 13. It is seen that the Q-phase remains cathodic in the Q-phase/Al couple in acidic, neutral and alkaline solutions indicating that the galvanic polarity of the Q-phase is independent of pH. The effect of the galvanic corrosion was largest at pH 2 and 13 compared to pH 6. The pH map obtained by SIET indicates that the galvanic activity of the Q-phase/Al couple proceeds via heavy alkalization of the Q-phase surface with the generation of appreciable amounts of OH- ions. The enrichment of Cu indicated by EDX is responsible for the observed cathodic activity of the Q-phase in the Q-phase/Al couple.
 Select A review—Pitting corrosion initiation investigated by TEM B. Zhang, X.L. Ma J. Mater. Sci. Technol., 2019, 35 (7): 1455-1465.  DOI: 10.1016/j.jmst.2019.01.013 Passive metals have superior resistance to general corrosion but are susceptible to pitting attack in certain aggressive media, leading to material failure with pronounced adverse economic and safety consequences. Over the past decades, the mechanism of pitting corrosion has attracted corrosion community striving to study. However, the mechanism at the pitting initiation stage is still controversy, due to the difficulty encountered in obtaining precise experimental information with enough spatial resolution. Tracking the accurate sites where initial dissolution occurs as well as the propagation of the dissolution by means of multi-scale characterization is key to deciphering the link between microstructure and corrosion at the atomic scale and clarifying the pitting initiation mechanism. Here, we review our recent progresses in this issue by summarizing the results in three representative materials of 316F, and Super 304H stainless steel as well as 2024-Al alloy, using in situ ex-environmental TEM technique.
 Select Effect of ordered helium bubbles on deformation and fracture behavior of α-Zr Si-Mian Liu, Shi-Hao Li, Wei-Zhong Han J. Mater. Sci. Technol., 2019, 35 (7): 1466-1472.  DOI: 10.1016/j.jmst.2019.03.015 Radiation-induced helium bubbles are detrimental to the mechanical properties of metals, usually causing severe hardening and embrittlement. Hexagonal close-packed (HCP) α-Zr alloys are one of the primary structural materials for nuclear applications, however, the effect of helium bubbles on their deformation and fracture behaviors still remains unexplored. Here, we found that ordered helium bubbles prefer to align along the basal plane in HCP α-Zr. Micro-scale in situ tensile tests revealed that helium bubbles less than 8 nm in size can increase the critical resolved shear stress of the prismatic slip. However, once the helium bubbles are larger than 8 nm, a bubble-softening effect happens due to a decrease in number density of helium bubbles and an increase in porosity. Once the Schmid factor of basal slip is considerably higher than prismatic slip, bubble coalescence along the basal plane becomes the major failure mode in helium-irradiated α-Zr.
 Select Deformation mechanism and dynamic precipitation in a Mg-7Al-2Sn alloy processed by surface mechanical attrition treatment Xiaoying Shi, Yangxin Li, Xiaoqin Zeng, Yong Liu, Bin Chen, Jian Lu, Dejiang Li J. Mater. Sci. Technol., 2019, 35 (7): 1473-1478.  DOI: 10.1016/j.jmst.2019.02.007 The effect of second phases on the deformation mechanism of as-cast, solution-treated and aged Mg-7Al-2Sn (AT72) alloys during surface mechanical attrition treatment (SMAT) was investigated. Twinning was suppressed in the alloys containing second phases, which can provide nonuniform microstructures and phase boundaries as dislocation sources. Dynamic precipitation in AT72 alloys was studied during SMAT deformation as well. Mg2Sn particles can dynamically precipitate on the surface of all AT72 alloys during SMAT process. The quantity of Mg2Sn particles in the as-cast alloy, which is determined by the initial quantity of second phases, is larger than that of T4 and T6 alloys after the SMAT process.
 Select Anomalous formation of micrometer-thick amorphous oxide surficial layers during high-temperature oxidation of ZrAl2 Zhangping Hu, Yifei Xu, Yuanyuan Chen, Peter Schützendübeb, Jiangyong Wang, Yuan Huang, Yongchang Liu, Zumin Wang J. Mater. Sci. Technol., 2019, 35 (7): 1479-1484.  DOI: 10.1016/j.jmst.2019.02.005 The thermal oxidation of ZrAl2 in the temperature range of 550-750 °C in pure oxygen has been investigated by a combinational experimental approach using X-ray diffraction, scanning electron microscopy/energy dispersive spectrometer, Auger electron spectroscopy and cross-sectional transmission electron microscopy. The thermal oxidation leads to the growth of anomalously thick (up to 4.5 μm) amorphous (Zr0.33Al0.67)O1.66 surficial layers at temperatures as high as 750 °C. The oxidation kinetics obeys a parabolic law with an activation energy of 143 kJ/mol. The underlying mechanism for the formation of such micrometer-thick amorphous oxide surficial layers has been discussed on the basis of interface thermodynamics and the occurrence of high interface stability associated with a synchronous oxidation of Al and Zr elements.
 Select Effect of cooling rate on phosphorus segregation behavior and the corresponding precipitation of γ″ and γ′ phases in IN718 alloy Anwen Zhang, Sha Zhang, Fang Liu, Feng Qi, Xiaoyu Yao, Yuanguo Tan, Dan Jia, Wenru Sun J. Mater. Sci. Technol., 2019, 35 (7): 1485-1490.  DOI: 10.1016/j.jmst.2019.02.006 Effect of segregation behaviors of P at different cooling rates on the precipitation of γ″ and γ′ phases and the corresponding strength are investigated. The precipitation of γ″ and γ′ phases during cooling is sensitive to P concentration. With increasing the concentration of P, the amount of γ″ and γ′ particles increases after air cooling. With decreasing the cooling rate, the accelerating effect of P on the precipitation of γ″ and γ′ phases decreased first and then increased, which demonstrates the concentration of P dissolved in the grain interior decreases first and then increases. The different effects of P on γ″ and γ′ phases with different cooling rates were analyzed by the kinetic characteristic of nonequilibrium grain-boundary segregation. The characteristic of nonequilibrium grain-boundary segregation of P in superalloy is further confirmed, and the phenomenon caused by critical cooling rate is captured.
 Select Synthesis of waterborne polyurethane using snow as dispersant: Structures and properties controlled by polyols utilization Changqing Fang, Shaofei Pan, Zhen Wang, Xing Zhou, Wanqing Lei, Youliang Cheng J. Mater. Sci. Technol., 2019, 35 (7): 1491-1498.  DOI: 10.1016/j.jmst.2019.03.017 Waterborne polyurethane (WPU) dispersions have gained attention towards environmentally-friendly synthesis. In this article, a series of waterborne polyurethane emulsions was successfully synthesized and extensively characterized in terms of thermal, mechanical properties, hydrophilic behavior and morphology. Snow was chosen as dispersant instead of commonly used water. Preparation parameters such as intrinsic properties and molecular weight of polyols were discussed systematically. A chain structure was confirmed by Fourier transform infrared (FT-IR) spectroscopy. When comparing the nature of the polyols (PPG, PEG and PNA, 2000 g/mol) of this study, as-synthesized polyether waterborne polyurethane provided higher solid content, viscosity and water-resistance. However, polyester waterborne polyurethane performed differently and it exhibited higher thermal stability and crystallinity. When comparing the samples (WPU-N210, WPU-N220, WPU-N230 and WPU-N240) with different molecular weight of the same polyol (PPG) used as soft segment, the emulsion WPU-N220 with molecular weight of 2000 g/mol PPG provided the highest solid content and lowest viscosity. It was observed that particle size was uniform and highly dispersed for all samples from TEM images. Thermogravimetric, differential scanning calorimetry (DSC) and X-ray diffraction results demonstrated that the emulsion WPU-N230 with molecular weight of 3000 g/mol PPG possessed higher thermal stability and crystallinity than the other samples. The reason was that the Tg and thermal stability were increased with increasing molecular weight. When molecular weight increased, the arrangement of soft segment became more regular and so did the regularity of the molecular chains. This work demonstrated that different polyols as soft segment applied could lead to great differences in the structure and property of the resulting WPU.
 Select Mechanical properties and corrosion behavior of selective laser melted 316L stainless steel after different heat treatment processes Decheng Kong, Chaofang Dong, Xiaoqing Ni, Liang Zhang, Jizheng Yao, Cheng Man, Xuequn Cheng, Kui Xiao, Xiaogang Li J. Mater. Sci. Technol., 2019, 35 (7): 1499-1507.  DOI: 10.1016/j.jmst.2019.03.003 Irregular grains, high interfacial stresses and anisotropic properties widely exist in 3D-printed metallic materials, and this paper investigated the effects of heat treatment on the microstructural, mechanical and corrosion properties of 316 L stainless steel fabricated by selective laser melting. Sub-grains and low-angle boundaries exist in the as-received selective laser melted (SLMed) 316 L stainless steel. After heat treatment at 1050 °C, the sub-grains and low-angle boundaries changed slightly, and the stress state and strength decreased to some extent due to the decrease of dislocation density. After heat treatment at 1200 °C, the grains became uniform, and the dislocation cells vanished, which led to a sharp decline in the hardness and strength. However, the ductility was improved after recrystallization heat treatment. The passive film thickness and corrosion potential of the SLMed 316 L stainless steel decreased after heat treatment, and the pitting potential also decreased due to the accelerated transition from metastable to steady-state pitting; this accelerated transition was caused by the presence of weak passive films at the enlarged pores after heat treatment, especially for an adequate solid solution treatment.
 Select Global optimum of microstructure parameters in the CMWP line-profile-analysis method by combining Marquardt-Levenberg and Monte-Carlo procedures Gábor Ribárik, Bertalan Jóni, Tamás Ungár J. Mater. Sci. Technol., 2019, 35 (7): 1508-1514.  DOI: 10.1016/j.jmst.2019.01.014 Line profile analysis of X-ray and neutron diffraction patterns is a powerful tool for determining the microstructure of crystalline materials. The Convolutional-Multiple-Whole-Profile (CMWP) procedure is based on physical profile functions for dislocations, domain size, stacking faults and twin boundaries. Order dependence, strain anisotropy, hkl dependent broadening of planar defects and peak shape are used to separate the effect of different lattice defect types. The Marquardt-Levenberg (ML) numerical optimization procedure has been used successfully to determine crystal defect types and densities. However, in more complex cases like hexagonal materials or multiple phases the ML procedure alone reveals uncertainties. In a new approach the ML and a Monte-Carlo statistical method are combined in an alternative manner. The new CMWP procedure eliminates uncertainties and provides globally optimized parameters of the microstructure.
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