Dislocation loops enhance wear resistance in Ti2Zr0.75NbVx lightweight refractory medium-entropy alloys via high thermal conductivity-promoted oxide film formation

Abstract

This study systematically investigates the friction and wear behavior of Ti₂Zr_0.75NbV_x (x = 0.25, 0.5, 0.75, 1) lightweight refractory medium-entropy alloys (MEAs) and the underlying wear resistance enhancement mechanisms through a combined approach of experimental characterization and molecular dynamics (MD) simulations. The results reveal that atomic size mismatch-induced lattice distortion promotes the accumulation of residual stress, thereby facilitating the formation of dislocation loops. These dislocation loop structures significantly enhance the thermal conductivity of the material. The improved thermal conductivity accelerates the formation of dense oxide films by promoting oxygen diffusion and homogenizing the surface temperature field during friction. The oxide films effectively suppress stress concentration and plastic deformation, leading to a remarkable reduction in wear. Among the investigated alloys, the V0.5 composition exhibits the optimal wear resistance, with its dislocation loop structure not only substantially increasing the thermal conductivity (increasing from 32.4 W/(m·K) to 37.1 W/(m·K)) but also achieving the lowest average friction coefficient (0.6239) and wear rate (3.1181 × 10⁻⁴ mm³/N·m) compared to other compositions. This work provides important theoretical insights and experimental support for optimizing the wear resistance of lightweight refractory MEAs.