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

• Published in: Materials letters Vol. 254; pp. 46 - 49
• Main Authors: Yang, Cheng, Aoyagi, Kenta, Bian, Huakang, Chiba, Akihiko
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.11.2019; Elsevier BV
• Subjects: Annealing; Casting alloys; Evolution; Heat treating; HfNbTaTiZr; High entropy alloys; High temperature; Materials science; Mechanical properties; Microstructure; Phase decomposition; Phase transformation; Precipitation hardening; Precipitation strengthening; Refractory alloys; Refractory high-entropy alloy (RHEA); Refractory materials; Phase transformation; Precipitation strengthening; High temperature; Refractory high-entropy alloy (RHEA); HfNbTaTiZr
• ISSN: 0167-577X; 1873-4979
• DOI: 10.1016/j.matlet.2019.07.027

•Precipitation hardening improved mechanical properties of HfNbTaTiZr alloys.•Stability of nanoprecipitates was investigated at high temperature.•Microstructure evolution at high temperature was revealed.•Microstructure was decomposed at high temperature above 1450 °C. 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 °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 °C for 24 h, 1200 °C for 24 h, 1400 °C for 24 h, and 1450 °C for 168 h. The hcp-1 phase appears at 1000 °C and gradually dissolves up to 1200 °C. When the temperature rises to 1400 °C, the hcp-1 phase disappears, and fine nanoprecipitates begin to form. After annealing at 1450 °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.