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.