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496 results on '"Li, Jin‐shan"'

11. Evading strength−ductility trade-off of GH605 alloy using magnetic field-assisted undercooling treatment

Author

HE, Yi-xuan, BU, Fan, BIAN, Zhang-chi, XIANG, Ming-xiu, ZHOU, Meng-meng, LIU, Xu-dong, ZHU, Lei, WANG, Jun, and LI, Jin-shan

Abstract

Undercooling solidification under a magnetic field (UMF) is an effective way to tailor the microstructure and properties of Co-based alloys. In this study, by attributing to the UMF treatment, the strength−ductility trade-off dilemma in GH605 superalloy is successfully overcome. The UMF treatment can effectively refine the grains and increase the solid solubility, leading to the high yield strength. The main deformation mechanism in the as-forged alloy is dislocation slipping. By contrast, multiple deformation mechanisms, including stacking faults, twining, dislocation slipping, and their strong interactions are activated in the UMF-treated sample during compression deformation, which enhances the strength and ductility simultaneously. In addition, the precipitation of hard Laves phases along the grain boundaries can be obtained after UMF treatment, hindering crack propagation during compression deformation.

Published
2024
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18. Tailoring crystal orientation and property of Cu−Co immiscible alloy during solidification under high magnetic field

Author

WEI, Chen, LI, Jin-shan, YAN, Yu-jie, HE, Yi-xuan, BEAUGNON, Eric, and WANG, Jun

Abstract

Non-equilibrium solidification experiments were conducted on Cu50Co50alloys under different magnetic field intensities to investigate the orientation, microstructure evolution, and magnetic properties of the Co-rich phase. The results revealed that the phase-separated rod-like Co-rich phase can realize the alignment morphology and can be oriented with the 〈111〉 crystal direction along the direction of the 5 T high magnetic field (HMF). In contrast, the orientation of the Cu-rich phase, which underwent secondary liquid−liquid phase separation, was not significantly affected by the HMF. The alloy solidified at 0 T showed near-magnetic isotropic behavior, while the alloy solidified at 5 T displayed magnetic anisotropic behavior. The saturation magnetization of the alloy increased slightly, and the coercivity decreased correspondingly, which were strictly dependent on the orientation evolution of the Co-rich crystal.

Published
2024
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41. Dry-sliding tribological properties of AlCoCrFeNiTi0.5 high-entropy alloy.

Author

Yu, Yuan, Wang, Jun, Li, Jin-Shan, Kou, Hong-Chao, Niu, Si-Zhe, Zhu, Sheng-Yu, Yang, Jun, and Liu, Wei-Min

Abstract

High-entropy alloys (HEAs), with a new alloying concept, could possess many unique mechanical and functional properties. The current work investigated whether one such alloy offers potential for bearing surfaces under dry conditions. The dry, reciprocating sliding wear characteristics of AlCoCrFeNiTi0.5 alloy were investigated under various applied loads and sliding speeds. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were utilized to characterize internal structure and wear surfaces of the alloy, respectively. It is found that the AlCoCrFeNiTi0.5 alloy preserves better wear resistance than Fe77Ni23 solid solution alloy, Ti-46Al-2Cr-2Nb intermetallic alloy, or a wear-resistant steel AISI 52100, especially under higher loads. The wear rate increases slowly with the applied loads increasing and keeps steady under different sliding speeds. The wear mechanisms are abrasive wear, adhesive wear and oxidative wear. The nano-sized Fe–Cr solid solution and Al–Ni–Ti rich intermetallic phase precipitated in the dendritic regions and the formation of oxidation play important roles in the good wear resistances of this high-entropy alloy. [ABSTRACT FROM AUTHOR]

Published
2022
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44. Influence of α+β solution treatments on Ti65 ultrathin sheets: Silicide precipitation, mechanical behaviour and novel {101¯1}twinning system

Author

ZHAO, Ding, FAN, Jiang-kun, ZHANG, Zhi-xin, WANG, Jing, WANG, Qing-jiang, CHEN, Zhi-yong, TANG, Bin, KOU, Hong-chao, and LI, Jin-shan

Abstract

To cope with the urgent demands of the aerospace industry for lightweight and excellent high-temperature performance titanium alloy components, the microstructure evolution, silicide precipitation and mechanical behaviour of a novel high-temperature Ti65 titanium alloy ultrathin sheet with different heat treatments were systematically investigated. Submicron (Ti,Zr)6Si3silicides are observed after solution treatments followed by air cooling, leading to a decline and significant fluctuations in tensile properties. For furnace cooling samples, (Ti,Zr)5Si3silicide crossing grain boundaries and (Ti,Zr)6Si3silicide near grain boundaries are observed after solution treatment at 950 °C. When the solution temperature increases to 1010 °C, the third silicide (Ti,Zr)3Si appears near dislocations. The combined effect of the strong size effect of the alloy ultrathin sheet and silicide precipitation results in great performance fluctuation, sharp drop of ductility and even brittle fracture. In addition, silicide precipitation differs little with various holding time during low-temperature solution treatment. Moreover, novel {101¯1}twins appear after the rolling process at 990 °C and are only inside coarse basal texture α grains, with an axis—angle pair of 65° 〈844¯3〉.

Published
2023
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45. Economic Security and the Political Governance Crisis in Central African Republic

Author

Thales Pacific Yapatake Kossele and Li Jin Shan

Subjects
Economic policy, 050204 development studies, media_common.quotation_subject, Corporate governance, 05 social sciences, Measures of national income and output, Wage, Foreign direct investment, Development, Goods and services, 0502 economics and business, Accountability, Economic security, Per capita, Economics, 050207 economics, media_common
Abstract

Recently the Central African Republic (CAR) has been experiencing huge economic insecurity which mostly derives from the political governance crisis that the country has been continuously undergoing since its independence in 1960. This paper examines the relationship between the political governance crisis and economic security in the country, covering the period 1996–2015, using two‐stage instrumental analysis and second order asymptotic tests. The results show that political stability and absence of violence/terrorism, voice and accountability, proxies of political governance crisis played a different role on national income per capita, agricultural raw materials exports, agriculture value added, external balance on goods and services, food exports, food imports, foreign direct investment, GDP growth, GDP per capita growth, wage and salaried workers, industry value added, total natural resources rent and trade, as proxies of economic security. The importance of sustainable political governance stability and the implementation of appropriate reforms at institutional level are preconditions to economic security.

Published
2018

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