Microstructure, phase stability and mechanical properties of Nb-Ni-Ti-Co-Zr and Nb-Ni-Ti-Co-Zr-Hf high entropy alloys

Owning to their excellent thermal stability and high strength at elevated temperature, high entropy alloys (HEAs) possess great potential for the application in aviation and aerospace fields. In present work, two novel Nb-Ni-Ti-Co-Zr and Nb-Ni-Ti-Co-Zr-Hf HEAs were prepared by arc melting and copper mold suction-casting method. The microstructure, phase stability, mechanical properties at room temperature and elevated temperature of the two HEAs were studied. Both of the HEAs possess high yield stress at room temperature, especially for the Nb-Ni-Ti-Co-Zr (with 2331. Mpa). In addition, the Nb-Ni-Ti-Co-Zr HEA exhibited high yield stress of 564. Mpa at elevated temperature of 800. °C and large compressive plastic strain (more than 50% at 800. °C). Nb-Ni-Ti-Co-Zr-Hf alloy showed new phase precipitation at 800. °C, whereas the structure of Nb-Ni-Ti-Co-Zr was more stable, which is one of the reason why it possesses high strength at room temperature and elevated temperature. The high temperature properties of the Nb-Ni-Ti-Co-Zr HEA make it promising for high temperature application.