The effect of heat treatment on the microstructure and wear resistance of CoCrFeNiNb0.45 high entropy alloy under different sintering states

Eutectic high entropy alloys (HEAs) have been extensively studied for the superior strength, and wear resistance. In this work, a CoCrFeNiNb 0.45 HEA with a eutectic microstructure was prepared via powder metallurgy, and the effects of sintering time and heat treatment (HT) temperature on the microstructure, precipitates, and wear behavior of the eutectic HEA were systematically studied. The results show that the as-sintered CoCrFeNiNb 0.45 HEA consists of a face-centered cubic (FCC) matrix and Nb-rich Laves phases. With prolonged sintering time, the microstructure gradually transforms from blocky-like Laves phase into a lamellar eutectic structure, and the relative density increases from 95.5% to 97.6%. The uniformly distributed Laves phases contribute to protecting the matrix, improving its hardness and wear resistance. After HT at 900 °C, a large number of needle-like ε and rod-like γʺ phases precipitate in the matrix, accompanied by the appearance of fine pores. When the HT temperature reaches 1000 °C, only rod-like precipitated phases are observed in the alloy. These precipitates contribute to the improvement of the matrix hardness, which increases by approximately 20%. Additionally, a higher HT temperature improving the material's relative density and eliminate pores. The precipitated phases improve the alloy's wear resistance by increasing the matrix strength, leading to a gradual transformation of the main wear mechanism from oxidative wear to abrasive wear.