Significantly Enhanced Wear Resistance of an Ultrafine-Grained CrFeNi Medium-Entropy Alloy at Elevated Temperatures
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INTRODUCTION
METALLIC alloys for mechanical components involving sliding contacts in relative motion, particularly at elevated temperatures, require not only a good combination of high strength and ductility but also high sliding wear resistance.[1–4] At or below room temperature (RT), sliding wear resistance largely depends on the strength and hardness of the metallic alloys as well as the sliding-induced microstructural evolution below the sliding surface.[3–7] However, at elevated temperatures, the moving surfaces are not only subjected to the stresses associated with frictional and contact forces but also susceptible to thermal softening and oxidation through their reaction with oxygen.[8] The elevated temperature sliding wear of metallic materials involves
DINGSHAN LIANG and PENGBO WEI are with the Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, Guangdong, P.R. China and also with the Department of Mechanical and Aerospace Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon 999077, Hong Kong, P.R. China. CANCAN ZHAO, FEILONG JIANG, and FUZENG REN are with the Department of Materials Science and Engineering, Southern University of Science and Technology. Contact e-mail: [email protected] WEIWEI ZHU is with the Department of Materials Science and Engineering, Southern University of Science and Technology and also with the Institute of Applied Physics and Materials Engineering, Faculty of Science & Technology, University of Macau, Macau 999078, P.R. China. Manuscript submitted September 12, 2019. Article published online April 13, 2020 2834—VOLUME 51A, JUNE 2020
surface deformation, subsurface damage accumulation, oxidation, material transfer, the formation of glaze layer, and the creation of wear debris.[1,9,10] Thus, unraveling the wear mechanism of metallic contacts at high temperature is still a challenge, which requires detailed characterization of the subsurface microstructure evolution. In particular, it is of great importance to investigate the microstructural, chemical and even mechanical characteristics of the glaze layer.[2,8,10–17] Moreover, besides the materials’ intrinsic properties, the wear performance and wear mechanism also correlate with testing conditions, such as temperature,[18] applied load,[19] sliding velocity,[20] and atmosphere,[21] as detailed in a systematic review on the mechanisms of sliding wear of metals and alloys at elevated temperatures in Reference 9. Therefore, the complicated extreme mechanical and thermal environment requires dedicated design of the grain structures of metallic alloys to suppress strain localization, accommodate large strain gradients, resist thermal softening, and establish a wear-protective glaze layer during sliding at elevated temperatures. To enable the pursuit of alloys with special microstructures and exceptional properties, a new alloy design strategy that incorporates multi-principal elements has been developed. According to the difference of
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