High temperature phase transformation and mechanical properties of Hf_0.25NbTa_0.25TiZr high-entropy alloys formed by laser melting deposition(LMD)

Refractory high-entropy alloys have received increasing attention in recent years, and laser additive manufacturing can effectively solve the formability dilemma faced by high-entropy alloys. In this paper, a Hf_0.25NbTa_0.25TiZr refractory high-entropy alloy with lower density than equal atomic ratio alloy was formed by laser melting deposition technology, and its high temperature mechanical behavior and microstructure phase transformation behavior were systematically analyzed. The BCC phase rich in Zr and Hf and the HCP phase rich in Zr and Ti elements will be precipitated successively at high temperature. The two precipitated phases were re-dissolved at 1200 °C, and a new HCP phase was precipitated at 1400 °C. The phase precipitation behavior has an effect on the distribution of small-angle misorientation in grains. The yield strength of the alloy at 600 and 800 °C is 675.0 and 409.5 MPa, respectively, which is 10.0 % and 17.9 % higher than that of the equiatomic as-cast alloy. The high temperature plastic transition temperature of the alloy is increased. The high temperature behavior of the alloy was systematically analyzed by Portevin-Le Chatelier effect and dynamic recrystallization theory.