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What is going on in magnesium alloys?
X.J. Wang, D.K. Xu, R.Z. Wu, X.B. Chen, Q.M. Peng, L. Jin, Y.C. Xin, Z.Q. Zhang, Y. Liu, X.H. Chen, G. Chen, K.K. Deng, H.Y. Wang
J. Mater. Sci. Technol.    2018, 34 (2): 245-247.   DOI: 10.1016/j.jmst.2017.07.019
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China has been developed into one of the most active regions in terms of both fundamental and applied research on magnesium (Mg) and its alloys in the world from a solid base laid by its prominent metallurgist and materials scientists over the past decades. Nowadays, a large number of young-generation researchers have been inspired by their predecessors and become the key participants in the fields of Mg alloys, which consequently led to the establishment of China Youth Scholar Society for Magnesium Alloys Research in 2015. Since then, the first two China Youth Scholars Symposiums on Mg Alloys Research had been held at Harbin (2015) and Chongqing (2016) China, respectively. A number of crucial research interests related to fundamental and applied Mg research were discussed at the conferences and summarized in this short perspective, aiming to boost far-reaching initiatives for development of new Mg-based materials to satisfy the requirements for a broad range of industrial employments. Herein, four main aspects are included as follows: i) Plastic deformation mechanism and strengthening strategy, ii) Design and development of new Mg-based materials, iii) Key service properties, and iv) New processing technologies.

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Enhanced localized and uniform corrosion resistances of bulk nanocrystalline 304 stainless steel in high-concentration hydrochloric acid solutions at room temperature
S.G. Wang, M. Sun, Y.H. Xu, K. Long, Z.D. Zhang
J. Mater. Sci. Technol.    2018, 34 (12): 2498-2506.   DOI: 10.1016/j.jmst.2018.06.006
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The localized and uniform corrosion resistances of bulk nanocrystalline 304 stainless steel (NC-304SS) produced by severe rolling technique, and its conventional polycrystalline 304 stainless steel (CC-304SS) counterpart, were investigated in high-concentration hydrochloric acid solutions at room temperature. NC-304SS can scarcely suffer from localized corrosion in 4 mol/L and 5 mol/L HCl solutions during 5-day immersion tests, and in 1-3 mol/L HCl solutions during thirty-five-day immersion tests. The corrosion rate of NC-304SS was also less than that of CC-304SS during these immersion tests. The improved localized and uniform corrosion resistances of NC-304SS were explained in terms of the adsorption and chemical activity of Cl- on NC-304SS and CC-304SS characterized by X-ray photoelectron spectroscopy, and the valence electron configurations of NC-304SS and CC-304SS were characterized by ultra-violet photoelectron spectroscopy rather than conventional electrochemical results.

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Characteristics of Oxidation and Oxygen Penetration of Alloy 690 in 600 °C Aerated Supercritical Water
Xiangyu Zhong, Xinqiang Wu, En-Hou Han
J. Mater. Sci. Technol.    2018, 34 (3): 561-569.   DOI: 10.1016/j.jmst.2016.11.001
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The oxide films formed on Alloy 690 exposed to 600 °C supercritical water were characterized using mass measurement, X-ray diffraction, Raman spectroscopy, scanning electron microscopy equipped with energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. It was found that the mass gain of the alloy in supercritical water decreased with increasing exposure time. The oxide films have a double-layer structure, with an inner layer rich in Cr and outer layer rich in Ni and Fe after short time and long time exposure. The penetration of the oxide along the grain boundaries was observed, and the penetration depth increased with increasing exposure time. The grain boundaries and voids are the short-path of oxygen diffusion into the metal.

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Effect of crystal orientation on corrosion behavior of directionally solidified Mg-4 wt% Zn alloy
Hongmin Jia, Xiaohui Feng, Yuansheng Yang
J. Mater. Sci. Technol.    2018, 34 (7): 1229-1235.   DOI: 10.1016/j.jmst.2017.06.009
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Microstructure and crystallographic orientation of directionally solidified Mg-4 wt% Zn alloy were characterized by X-ray computed tomography (XCT) and electron backscatter diffraction (EBSD) in this study. Results reveal that Mg-4 wt% Zn alloy with dendritic microstructure exhibits typical {0002} basal texture along growth direction. Based on this, the effect of grain orientation on corrosion behavior of directionally solidified Mg-4 wt% Zn alloy in 0.9 wt% NaCl solution was investigated. Result shows that {0002} oriented planes have better corrosion resistance than {11\(\overline{2}\)0} and {10\(\overline{1}\)0} ones, which is attributed to a synergistic effect of surface energy, atomic packing density and the stability of oxidation film.

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Effect of grain size on mechanical property and corrosion resistance of the Ni-based alloy 690
Jinlong Lv
J. Mater. Sci. Technol.    2018, 34 (9): 1685-1691.   DOI: 10.1016/j.jmst.2017.12.017
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Mechanical property of coarse grained and nano/ultrafine grained alloy 690 and their corrosion resistance after immersion in high temperature borate buffer solution were investigated. The grain refinement significantly enhances the tensile strength of the alloy 690. In addition, the grain refinement facilitates the formation of the deformation twin which improves the ductility of the alloy 690. It has been found that the grain refinement promotes to form more Cr2O3 on the surface of the alloy 690 in high temperature borate buffer solution. At the same time, the grain refinement inhibits the formation of spinel type oxides. More hematite type oxides formed on nano/ultrafine grained alloy 690 improves its corrosion resistance in borate buffer solution. The hematite type oxides have a lower concentration of point defect than that of the spinel type oxides, which results in an excellent corrosion resistance of nano/ultrafine grained alloy 690. These results are supported by the Mott-Schottky analysis and the point defect model.

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Effect of fluoride on the corrosion behavior of nanostructured Ti-24Nb-4Zr-8Sn alloy in acidulated artificial saliva
Ji Li, Yun Bai, Zhidong Fan, Shujun Li, Yulin Hao, Rui Yang, Yongbo Gao
J. Mater. Sci. Technol.    2018, 34 (9): 1660-1670.   DOI: 10.1016/j.jmst.2018.01.008
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The surface of titanium dental implants is highly susceptible to aggressive fluoride ions in the oral environment. Nanotechnology has proven an effective approach to improve the stability and corrosion resistance of titanium by applying a passive film. In this study, we investigated the effects of fluoride on the corrosion behavior of nanostructured (NS) Ti-24Nb-4Zr-8Sn (Ti2448) alloy in acidulated artificial saliva (AAS) at 37 °C, and then conducted comparisons with its coarse grained (CG) counterpart. Electrochemical techniques, such as potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), as well as surface analysis including X-ray photoelectron spectroscopy (XPS) with argon ion sputtering, and scanning electronic microscopy (SEM) were employed to evaluate the effects of fluoride on sensitivity to pitting and the tolerance of Ti2448 to fluoride in AAS solution. The results demonstrate that corrosion current density increased with F- concentration. In all respects, the NS Ti2448 alloy presented corrosion resistance superior to that of its coarse grained (CG) counterpart at low F- concentrations (≤0.1%). Furthermore, a high content of F- (1%) was shown to promote the active dissolution of both alloys by increasing the rate of corrosion. Following immersion in the fluoridated AAS solution for 60 days, a tissue-friendly compound, Ca3(PO4)2, was detected on the surface of the NS when F- = 0.01% and Na2TiF6 was identified as the main component in the corrosion products of the CG as well as NS Ti2448 alloys when F- = 1%. High concentrations of F- produced pitting corrosion on the CG alloy, whereas NS Ti2448 alloy presented general corrosion in the form of lamellar separation under the same conditions. These findings demonstrate the superior corrosion resistance of the NS Ti2448 alloy as well as lower pitting sensitivity and higher tolerance to fluoride due mainly to grain refinement.

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Electrochemical noise analysis on the pit corrosion susceptibility of biodegradable AZ31 magnesium alloy in four types of simulated body solutions
Changgang Wang, Liping Wu, Fang Xue, Rongyao Ma, Ini-Ibehe Nabuk Etim, Xuehui Hao, Junhua Dong, Wei Ke
J. Mater. Sci. Technol.    2018, 34 (10): 1876-1884.   DOI: 10.1016/j.jmst.2018.01.015
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Magnesium alloys have been investigated as biodegradable implant materials since the last century. Non-uniform degradation caused by local corrosion limits their application, and no appropriate technology has been used in the research. In this study, electrochemical noise has been used to study the pit corrosion on magnesium alloy AZ31 in four types of simulated body solutions, and the data have been analyzed using wavelet analysis and stochastic theory. Combining these with the conventional polarization curves, mass loss tests and scanning electron microscopy, the electrochemical noise results implied that AZ31 alloy in normal saline has the fastest corrosion rate, a high pit initiation rate, and maximum pit growth probability. In Hanks’ balanced salt solution and phosphate-buffered saline, AZ31 alloy has a high pit initiation rate and larger pit growth probability, while in simulated body fluid, AZ31 alloy has the slowest corrosion rate, lowest pit initiation rate and smallest pit growth probability.

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Microstructure and corrosion behavior of the heat affected zone of a stainless steel 308L-316L weld joint
Cheng Ma, Qunjia Peng, Jinna Mei, En-Hou Han, Wei Ke
J. Mater. Sci. Technol.    2018, 34 (10): 1823-1834.   DOI: 10.1016/j.jmst.2017.12.016
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Microstructure of the heat affected zone (HAZ) of a 308L-316L stainless steel (SS) weld joint and its corrosion behavior in high temperature water were studied. Peak of the residual strain was observed to approach to the fusion boundary in the HAZ while the strain increased from the top to root areas of the HAZ. The root area of the HAZ shows a lower corrosion resistance in high temperature water than the top and middle areas of the HAZ. This is attributed to a higher level of residual strain in association with a higher density of tangled dislocations in the top area of the HAZ. The results suggest that the residual strain in the HAZ could also promote the SCC through its effect on corrosion, in addition to that on the local microstructure and mechanical property of the steel.

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Effect of cumulative gamma irradiation on microstructure and corrosion behaviour of X65 low carbon steel
Canshuai Liu, Jianqiu Wang, Zhiming Zhang, En-Hou Han, Wei Liu, Dong Liang, Zhongtian Yang, Xingzhong Cao
J. Mater. Sci. Technol.    2018, 34 (11): 2131-2139.   DOI: 10.1016/j.jmst.2018.03.017
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X65 low carbon steel was exposed to Co-60 radiation source with 1.25 MeV gamma rays, and cumulatively absorbed gamma irradiation doses (1, 2, and 3 MGy) were obtained after different exposure time (333, 667, and 1000 h). The effect of cumulative gamma irradiation on microstructure and corrosion behaviour of the carbon steel in unirradiated aerobic Beishan groundwater at 25 °C was investigated by using positron annihilation, scanning vibrating electrode, and electrochemical techniques. Cumulative gamma irradiation increases vacancy intensity and decreases open circuit potential (OCP) of carbon steel. They indicate that the irradiated carbon steel is activated. Measured current density distribution above the irradiated carbon steel shows that cumulative gamma irradiation accelerates localized corrosion after 0.5 h of immersion. In contrast, the analysis of electrochemical impedance spectroscopy of the irradiated carbon steel indicates that localized corrosion is transformed into general corrosion after 12 h of immersion, which is also accelerated by cumulative gamma irradiation.

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Corrosion protection of waterborne epoxy coatings containing mussel-inspired adhesive polymers based on polyaspartamide derivatives on carbon steel
Mingliang Yang, Jianhua Wu, Daqing Fang, Bo Li, Yang Yang
J. Mater. Sci. Technol.    2018, 34 (12): 2464-2471.   DOI: 10.1016/j.jmst.2018.05.009
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A novel mussel-inspired adhesive polymer (PHEA-DOPA) containing the 3,4-dihydroxyphenylalanine (DOPA) functional group based on polyaspartamide derivatives was synthesized. The corrosion protection of the waterborne epoxy coatings containing the adhesive polymers was investigated by electrochemical impedance spectroscopy (EIS). The results indicated that the PHEA-DOPA could improve the corrosion resistance of the waterborne epoxy coating. The corrosion products were also analyzed by Raman microspectroscopy (RM), indicating the formation of the insoluble DOPA-Fe complexes on the carbon steel surface. These complexes simultaneously acting as a passivating layer, can inhibit the process of corrosion at the metal-solution interface. The differential scanning calorimeter (DSC) measurement indicated that PHEA-DOPA can increase the crosslinking density of coating. The effect of O2 on the protective mechanism of the PHEA-DOPA coating in a 3.5% NaCl solution was also evaluated by EIS. The results indicated that the barrier effect was significantly improved under aerated conditions because DOPA was oxidized to DOPA-quinone (Dq) by O2, which triggered the reaction with Fe ions that were released from the surface of the carbon steel. This led to more compact coatings.

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ISSN: 1005-0302
CN: 21-1315/TG
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