Effect of Cr content on microstructure characteristics and mechanical properties of ZrNbTaHf0.2Crx refractory high entropy alloy

Introducing Laves phase into refractory high entropy alloys is a new exploration direction to improve the alloy strength. The as-cast and annealed states ZrNbTaHf0.2Crx (x = 0, 0.3, 0.5, 0.75, 1.0) alloys were prepared, and the microstructure, phase constituents, and mechanical properties of the refractory high-entropy alloy were studied in the present work. The addition of Cr elements affects the alloy properties mainly through the formation of the high-entropy Laves phase. The ZrNbTaHf0.2Crx alloys have a typical dendritic structure, consisting of BCC solid solution phase, HCP solid solution phase and C15 Laves phase. With the increasing Cr content, the fraction of Laves phase increases significantly. The heat treatment results in more fraction of the C15 Laves phase and BCC phases. After annealing, the growth of BCC phase has no obviously preferred orientation. The hardness and strength significantly increase with Laves phase with a compromise in ductility. The solid solution strengthening caused by significant lattice distortion and laves phase precipitation increase the strength and hardness of the alloys.