Microstructure and Wear Behavior of High-Carbon Concentration CrCoNi Multi-principal Element Alloys

CrCoNi multi-principal element alloys (MPEAs) have shown good strength-ductility combinations, but few other mechanical properties have been evaluated in these alloys so far. Although optimal wear-resistant alloys depend upon the intended application, a hard and tough material is often desirable. In this work, as-cast Cr₄₀Co₄₀Ni₂₀ was tested for wear under dry-sliding conditions against an alumina pin, exhibiting good wear resistance and low coefficient of friction (CoF) of 0.12. To further improve the wear behavior, carbon (C) additions were evaluated in this alloy and in Cr₄₀Co₃₀Ni₃₀, up to the liquid solubility limit at 1600 °C (~24 at. pct C). Alloy design was performed using computational thermodynamic calculations. Predicted microstructures contain: self-lubricating graphite flakes, hard primary Cr-rich carbides, and a tough eutectic matrix; in good agreement with experimental results. As-cast Cr₄₀Co₄₀Ni₂₀-C, even without microstructural refinement, displayed low specific wear rate (on the order of 10⁻⁴ mm³/Nm) and moderate CoF (0.55-0.62). Its performance was hampered by the fracture and detachment of coarse primary carbides, which introduced an additional abrasive element into the tribosystem. These findings indicate that C additions to CrCoNi alloys, along with the refinement of primary carbides, represent a promising strategy to further improve the wear performance of MPEAs.