Heat treatment effects on microstructure and mechanical properties of TiZrNbTa high-entropy alloy

Microstructure and mechanical properties of TiZrNbTa high-entropy alloy (HEA) in the as-cast and annealed states are systematically investigated. The yield strength of TiZrNbTa HEA strongly depends on the heat treatment temperatures. With the increase of heat treatment temperature, the yield strength of TiZrNbTa increases first and then decreases. When the heat treatment temperature reaches 600 ℃, the yield strength and uniform strain of TiZrNbTa HEA are 1583 ± 55 MPa and 20.5% ± 1.8%, respectively. Compared with the as-cast state TiZrNbTa, the yield strength of TiZrNbTa HEA after simple heat treatment, i.e., 600 ℃ for 1 h improves by 47%, which is attributed to the spinodal decomposition strengthening. By comparing the contribution of grain boundary strengthening for the TiZrNbTa HEA before and after annealing, the significant decrease in the yield strength of the TiZrNbTa HEA is not caused by grain coarsening after heat treatment at 800 ℃, but by the formation of a vein-like phase in grain boundaries. The Ti(Zr)-rich and Nb(Ta)-rich phases in TiZrNbTa HEA exhibit different performances in large compressive strain conditions. The Ti(Zr)-rich phase exhibits good compressive plastic deformation ability, and the Nb(Ta)-rich phase has a higher strength. The TiZrNbTa HEA after one-step simple heat treatment displays excellent mechanical properties, which significantly improves the possibility of clinical application as a new orthopedic-implant alloy.