Microstructure evolution and mechanical property of a precipitation-strengthened refractory high-entropy alloy HfNbTaTiZr

摘要

The mechanical properties and microstructure evolution of a precipitation-strengthened refractory high-entropy alloy, HfNbTaTiZr, with equiaxed grains are reported. The as-cast alloy shows a high yield strength of 356 MPa at 1200 degrees C, and 1597 MPa with good ductility at room temperature. The enhancement in strength is attributed to precipitation strengthening. Afterwards, microstructure evolution was investigated under several annealing treatment conditions: 1000 degrees C for 24 h, 1200 degrees C for 24 h, 1400 degrees C for 24 h, and 1450 degrees C for 168 h. The hcp-1 phase appears at 1000 degrees C and gradually dissolves up to 1200 degrees C. When the temperature rises to 1400 degrees C, the hcp-1 phase disappears, and fine nanoprecipitates begin to form. After annealing at 1450 degrees C for one week, however, this alloy exhibits phase decomposition. With the formation of two kinds of new fcc phase, fine nanoprecipitate only remains in bcc matrix, and another new hcp-2 phase forms in the grain. (C) 2019 Elsevier B.V. All rights reserved.