An atomic insight into the stoichiometry effect on the tribological behaviors of CrCoNi medium-entropy alloy

Face-centered cubic CrCoNi medium-entropy alloy (MEA) as one of the derivatives of CoCrFeMnNi high-entropy alloy has drawn much attention due to its remarkable mechanical properties. However, tribological behaviors of the CrCoNi MEA have been rarely reported. Herein, using large-scale molecular dynamics simulations, we explore friction and wear mechanisms of the CrCoNi MEA with varying Cr content. Results indicate that the decrease of Cr content leads to the decrease in the friction coefficient, but the increase in both hardness and normal force, regardless of the scratching depth. The resisting force on the indenter at the same scratching depth is inversely proportional to the initial content of Cr in the CrCoNi MEA. Moreover, the friction induces formation of the repulsive layer being mainly composed of Ni atoms. The proportion of Ni atoms in the repulsive layer varies with the scratching depth and Cr content. Our simulation results and findings shed lights on improving tribological performance via tailoring elemental composition in high- and medium-entropy alloys.