Effect of Zr content on microstructure and mechanical properties of AlCoCrFeNi high entropy alloy

Abstract

The AlCoCrFeNiZrx alloys are produced by electric arc melting and their microstructure and mechanical properties were analyzed. The alloys present two types of microstructures. One is a periodic structure consisting of the ordered BCC phase and BCC solid solution phase caused by spinodal decomposition, and the other is a mixture of the ordered BCC phase and Laves phase which nucleate and grow alternatively. The coexistence of ordering and spinodal decomposition can be attributed to the lattice strain caused by the addition of Zr element with a large atom radius. The criteria (ΔHmix and ΔR) cannot effectively predict the phases for the AlCoCrFeNiZrx alloys and the Laves phase even appears in the AlCoCrFeNiZr0.008 alloy. The compressive test shows that minor Zr addition can significantly improve the mechanical properties. The AlCoCrFeNiZr0.008 alloy has the yield strength of 1560MPa, fracture strength of 3513MPa and plastic strain of 29.5%, which are increased by 240MPa, 843MPa and 7% compared with the AlCoCrFeNi alloy, respectively. However, when the Zr content is above 0.1, the fracture strength and plastic strain decrease significantly although the yield strength of the alloys increases with the Zr content further increasing.