Research status of tribological properties optimization of high-entropy alloys: a review

High-entropy alloys (HEAs) have attracted extensive attention due to their excellent mechanical properties, thermodynamic stability, tribological properties, and corrosion resistance. In this paper, the tribological properties of HEAs were reviewed, including definition and preparation method of HEAs, testing and characterization method of tribological properties, influence of HEAs components on tribological properties, and anti-wear effect of process optimization. Firstly, the definition of HEAs and the enhancement of high-entropy effect, lattice distortion effect, delayed diffusion effect, and "cocktail " effect were briefly introduced. The advantages and disadvantages of current smelting and powder metallurgy methods were summarized, and various additive manufacturing techniques were discussed for preparing HEAs coatings. Secondly, the testing techniques and characterization methods of tribological properties of alloys were introduced. According to different wear mechanisms, the wear was classified as abrasive wear, adhesive wear, fatigue wear, corrosion wear, and oxidation wear. The research on reactive wear reduction, a new hotspot, was emphatically discussed. Furthermore, the influence of various metal elements and non-metal elements B, C, N, O, and Si in HEAs on tribological properties was analyzed, as well as the anti-wear mechanisms in the doped hard phases and self-lubricating phases. Meanwhile, the strengthening effects of surface remelting, heat treatment, and surface ceramization on the wear resistance of HEAs were reviewed. Finally, although some achievements have been made so far, there are still many challenges in the development of wear resistance for HEAs, and suggestions for future research directions were presented. [GRAPHICS]