Microstructure, mechanical properties and tribological behaviors of (Co0.33Ni0.33Cr0.23Mo0.1)80−xNbx(B0.3Si0.7)20 high entropy amorphous alloy coatings

Abstract

The (Co0.33Ni0.33Cr0.23Mo0.1)80−xNbx(B0.3Si0.7)20 high entropy amorphous alloy coatings (denoted as Nbx, x = 0, 2 and 4 at%) are successfully prepared by HVAF thermal spraying. The microstructure, mechanical properties and tribological behaviors of the as-sprayed coatings were comparatively investigated. The microstructure of as-sprayed coatings consists of amorphous phases, face-centered cubic (FCC) and (Cr, Mo)xB phases. Notably, the GFA (Glass-forming ability) of the as-sprayed coatings is improved and the precipitation of (Cr, Mo)xB phases is limited with the addition of Nb. The face-centered cubic (FCC) and (Cr, Mo)xB phases decrease with the Nb content increasing, and the Nb4 coating almost has a full amorphous structure. The Vickers hardness improves from 568.2 HV of Nb0 coating to 707.9 HV of Nb4 coating. The nanoindentation results indicate that the addition of Nb enhances the plastic deformation resistance and uniform deformation capacity of the coatings. For the as-sprayed coatings, the evolutions of tribological behaviors are consistent with the structural and mechanical variations. The addition of Nb decreases the oxidation wear and adhesion wear during friction process, which are the main wear failure mechanisms of as-sprayed coatings. The wear resistances of Nb4 coatings is increased by 49.54 % compared with that of the Nb0 coating, and the friction running-in time is decreased by 18.26 %.