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TRODUCTION

THE conventional alloy design concept is generally based on one or two major elements with the addition of a minor amount of alloying elements to achieve the desired properties. In the past 15 years, a novel alloy design strategy with multi-principal elements (MPE) in equiatomic or near-equiatomic concentrations has been developed. These alloys are referred to as high-entropy alloys (HEAs) or multi-principal element alloys (MPEAs).[1–3] The term ‘high entropy’ motivates a definition based on the magnitude of configurational

LU YANG, CANCAN ZHAO, ZHUO CHENG, and FUZENG REN are with the Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen, Guangdong 518055, China. Contact e-mail: [email protected] WEIWEI ZHU is with the Institute of Applied Physics and Materials Engineering, Faculty of Science & Technology, University of Macau, Macau, China and also with the Department of Electromechanical Engineering, Faculty of Science and Technology, University of Macau, Macau, China. PENGBO WEI is with the Department of Materials Science and Engineering, Southern University of Science and Technology and also with the Department of Mechanical and Aerospace Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China. Manuscript submitted October 16, 2019. Article published online April 19, 2020 2796—VOLUME 51A, JUNE 2020

entropy. In ideal solid solutions, the configurational entropy, DSconf =  RRniln(ni), where ni is the atomic fraction of the ith element and R is the gas constant, increases with the number of alloying elements. Based on this definition, the alloys can be divided into low-entropy alloys (DSconf < 0.69R), medium-entropy and HEAs alloys (0.69R £ DSconf £ 1.61R), (DSconf > 1.61R).[3] Within the family of HEAs, the single-phase face-centered-cubic (fcc) CoCrFeMnNi Cantor alloy has been one of the most extensively investigated alloys owing to its outstanding ductility,[4] radiation tolerance,[5] and fracture toughness especially at cryogenic temperatures.[6] However, this alloy suffers from low strength (usually < ~ 400 MPa) at ambient temperature due to its intrinsic fcc structural characteristics.[4,7–9] Despite the various mechanisms that have been developed to improve the strength of fcc HEAs, overcoming the strength/ductility trade-off of HEAs remains a challenge. Regarding the sliding wear behavior of Cantor-alloy-based HEAs systems, earlier studies mainly focused on exploring the effects of the addition of different alloying elements,[10–14] such as Al,[10] Ti,[11] Fe,[12] and V,[13] on the microstructure, wear performance, and wear mechanism at room temperature (RT) under dry sliding condition. The HEAs were observed to exhibit better wear resistance than conventional wear-resistant alloys with the same level of hardness. Even under

METALLURGICAL AND MATERIALS TRANSACTIONS A

lubrication condition, the AlCoCrFeNiCu HEA also exhibited high wear resistance and the wear mechanism showed signs of inhomogeneo