Achieving considerable wear resistance in new Ti-based high-entropy alloys through microstructural hardening by adding Nb

Abstract

In this study, (CoCrNiMn)₇₈Ti_22−xNb_x eutectic high-entropy alloys were successfully synthesised via an arc melting process under vacuum, and the phase structure, microstructure, mechanical properties and dry sliding tribological behaviour of the alloys were systematically investigated. The XRD results for the (CoCrNiMn)₇₈Ti_22−xNb_x eutectic high-entropy alloys are almost in agreement with the JMatPro phase diagram simulations, and the volume fraction of the Laves phase increased with increasing Nb content. OM and SEM images revealed that the microstructure was composed of dendrites (BCC A2) and interdendrites (BCC B2 +Laves) and changed from a hypoeutectic to a eutectic to a BCC B2 +Laves dual-phase structure, with the average grain size decreasing from 6.715 µm to 6.391 µm. Ti promoted the growth of the layered Laves phase and provided the alloy with base hardness and wear resistance. The hardness of the alloy combination of 21 % Ti and 1 % Nb reached the maximum value of 707.04 HV, whereas the average coefficient of friction (COF) and wear rate reached the lowest values of 0.49 and 1.668 × 10⁻⁴ mm³/N·m, respectively. With increasing load, the wear mechanism was mixed fatigue, delamination wear, and abrasive wear accompanied by oxidation, and the possibility of three-body wear paths between compacted tribolayers cannot be excluded. The debris was mostly in the form of microclusters, and the particle size range was concentrated between 1 −2 µm; meanwhile, the shape of the debris tended to develop from lamellar to spherical with increasing hardness.