Tuning the mechanical and high temperature tribological properties of Co-Cr-Ni medium-entropy alloys via controlling compositional heterogeneity.

• Mechanical and tribological behaviors of CoCrNi MEA are tuned by heterogeneous (Al,Ti). • Heterogeneous (Al,Ti) boosts the strength-plasticity synergy via solute strengthening. • Heterogeneous (Al,Ti) amplifies the wear of CoCrNi MEA at intermediate temperature. • Top glaze-layer enriched in (Al,Ti) contributes to high wear resistance at 800 °C. CoCrNi medium-entropy alloys (MEAs) system has been hailed as the potential high strength and ductile structural materials. However, the study on their tribological behaviors over a wide temperature range is still scarce. The current work investigates the effects of heterogeneous (Al, Ti) on the phase evolution, mechanical and high-temperature tribological performances of the MEAs. (Al, Ti) endows the MEAs a considerable solutal effect, which triggers the transformation from FCC-dominated single-phase structure to dual heterostructure containing FCC matrix and yarn-like structures/coupled BCC phases. Our designed MEA has an ultrahigh compressive yield strength of 2.0 GPa and a plasticity of 12.3%. Tribological properties of the designed MEA are temperature dependent. (Al, Ti) enhances the wear-resistance of MEA by five times due to the mitigation of abrasive wear below 400 °C. While between 400 °C and 600 °C, (Al, Ti) intensifies the adhesive wear instead, leading to severe wear. When it reaches 800 °C, (Al, Ti) will induce the tribo-chemistry to form the lubricative glaze-layer that minimizes wear. [ABSTRACT FROM AUTHOR]