Friction-induced rapid amorphization in a wear-resistant (CoCrNi)₈₈Mo₁₂ dual-phase medium-entropy alloy at cryogenic temperature

The CoCrNi medium-entropy alloy (MEA) has been proven to have excellent mechanical properties under cryogenic temperatures. Its low yield strength, however, limits practical application under harsh conditions, e.g., wear. Here, the (CoCrNi)₈₈Mo₁₂ dual-phase MEA, comprising a ductile face-centered cubic (FCC) matrix and a hard σ phase, was fabricated to strengthen the matrix and achieve excellent cryogenic wear performance. A significant wear reduction of 73% is achieved as the temperature decreases from 233 K to 113 K. It is found that the friction-induced amorphous layer underneath the worn surface contributes to excellent wear behaviors at 113 K, and amorphization would be rapidly occurred within 10 s. A lower stacking fault energy of CoCrNi-rich matrix at cryogenic temperature and a high solute concentration of Mo contribute to more defect accumulation and increased free energy of the system for amorphization. The current work clarifies the cryogenic wear mechanisms of the (CoCrNi)₈₈Mo₁₂ dual-phase MEA and provides a novel strategy for designing wear-resistant alloys via friction-induced rapid amorphization.