Enhancing mechanical properties and tribological performance of CoCrFeNi alloys via undercooling treatment

CoCrFeNi high-entropy alloys (HEAs) are promising for excellent ductility and toughness, but their low strength and poor wear resistance at room temperature limit the engineering applications as sliding components. To overcome that drawback and widen the service temperature range, in this work, the mechanical property and tribological performance at room/cryogenic temperature conditions were investigated for alloys. Compared with the as-cast alloy with FCC dendrite and BCC inter-dendrite dual phases, FCC phase transited into refined equiaxed grains and fractions of Cr-rich BCC precipitates increased within the undercooled alloy, increasing the strength and hardness to 240 MPa and 183 HV, respectively. The coefficient of friction (COF) kept stable (∼0.5) while the wear rate reduced to 6.49 × 10⁻⁵ mm³/(N·m), where the island-shaped oxide layers appear on the wear scar and the abrasive and adhesive wear behaviors dominates. Under cryogenic condition at 153 K, the wear rates were further decreased by 86.3 % with a reduced COF of 0.2, respectively, governed by the adhesive wear mechanism. The undercooling treatment for CoCrFeNi HEA can effectively improve mechanical properties and wear resistance at different operating conditions, especially for the cryogenic atmosphere. This work provides guidance for the optimizations of tribological and mechanical performance of HEAs.