Unveiling microstructural evolution and enhanced wear resistance of Co37Cr28Ni31Al2Ti2 multicomponent alloy via high-carbon addition

As a representative multicomponent alloy (MA) system, CoCrNi MAs and their derivatives have shown good strength-ductility combinations but the friction behaviors have been less studied. In this work, the influence of high-carbon addition on the microstructure, (nano)hardness, and wear behavior of the Co37Cr28Ni31Al2Ti2 MA are investigated in detail. Different from the face-centered-cubic (FCC) solid solution and ordered L12 precipitates in the base alloy, massive orthorhombic (Cr,Co,Ni)7C3 and FCC (Cr0.2Ti0.8)C particles together with some long-strip-shaped graphite-3R crystals appear in the L12-strengthened FCC matrix for the high-carbonbearing sample, resulting in an enhancement of hardness from 292 +/- 11 HV to 581 +/- 29 HV. Moreover, the wear rates (WRs) and the friction coefficients (COFs) under dry sliding conditions for the base alloy are measured to be -9.55 x 10-5 mm3/N center dot m and -0.6, and -6.02 x 10-4 mm3/N center dot m and -0.8, respectively, at loads of 2 N and 10 N. After adding carbon, the wear resistance is significantly improved (average WR: -2.81 x 10-6 mm3/ N center dot m and -1.89 x 10-5 mm3/N center dot m; average COF: -0.5 and -0.7 at loads of 2 N and 10 N). This improvement surpasses similar compositions prepared by casting and is comparable to surface-treated MAs. During friction and wear experiments, the fracture and detachment of hard carbides introduce additional abrasive particles into the tribosystem, resulting in a transformation from adhesive wear-dominated to abrasive wear-dominated. The wear resistance enhancement and friction mechanism transformation are further evidenced by the surface morphologies of the alumina counterbody materials after friction. The present findings indicate that the in-situ formation of carbides should be a promising strategy to enhance the wear resistance of MAs.