Oxide dispersion strengthening of CoCrNi medium entropy alloy using TiO2 particles

Abstract

Oxide dispersion strengthening (ODS) of CoCrNi medium entropy alloy (MEA) was studied in this work. To achieve this, a series of (CoCrNi)100-x(TiO2)x (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) MEAs was fabricated by vacuum arc melting, homogenization, hot-rolling and annealing instead of the commonly used powder metallurgy and mechanical alloying for ODS alloys. The MEAs remained FCC solid solution with TiO2 particles uniformly distributed, and the grain size decreased with the TiO2 content. The addition of TiO2 led to improved mechanical properties. While the ultimate tensile strength and fracture elongation were 866 MPa and 77%, respectively, at x = 0, they were 1130 MPa and 65% at x = 0.4. Both the yield strength and ultimate tensile strength were enhanced significantly without losing too much ductility, and it was mainly attributed to grain refinement and ODS. Compared with other cast CoCrNi MEAs with metal element additions, TiO2 particles addition yielded the dominance of grain refinement and ODS led to enhanced strength without losing too much ductility. Compared with other ODS MEAs fabricated by powder metallurgy, cast ODS CoCrNi MEAs consisted of larger grains and lower density of dislocations leading to much higher ductility but slightly lower strength.