Remarkably high fracture toughness of HfNbTaTiZr refractory high-entropy alloy

High-entropy alloys (HEAs) with face-centered cubic (FCC) phase such as CoCrFeMnNi or CoCrNi generally exhibit ultra-high fracture toughness but relatively low strength. In contrast, body-centered cubic (BCC) HEAs often display higher strengths, but the few reports on fracture toughness measurement demonstrate low toughness values. Here we show that the BCC HfNbTaTiZr refractory HEA, which possesses a combination of high strength, good tensile ductility and excellent high-temperature properties, also exhibits a remarkably high fracture toughness. By using the "single specimen" compliance method for J-integral measurement according to the ASTM E1820-17 standard, its fracture toughness K-JIC was experimentally determined to be 210 MPa m(1/2), which renders this HEA among the toughest metallic materials. The excellent damage tolerance makes the HEA promising for applications as high-temperature structural materials such as in aerospace field. (C) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.