A refractory medium-entropy alloy with ultrahigh specific yield strengths for elevated-temperature applications

Refractory high- or medium-entropy alloys (RHEAs or RMEAs) with excellent high-temperature mechanical properties and softening resistance have been proven to be the potential candidates for advanced engineering applications. However, room temperature brittleness and high density have become an important challenge that needs to be addressed. In this work, the tensile mechanical behavior and the underlying deformation mechanisms of lightweight Ti40Zr20Nb13.33V26.67 RMEA at 298 and 873 K were investigated systematically. The results showed that the as-cast RMEA has a single body-centered cubic phase and low density (5.88 g/cm3) and exhibits excellent mechanical properties at 298 K, with yield strength of 1033.9 MPa, specific yield strength of 175.8 MPa·cm3/g, and tensile fracture strain of 5.3%. More importantly, it also exhibits ultrahigh strength and sufficient ductility at 873 K, with yield strength of 783.2 MPa, specific yield strength of 133.2 MPa·cm3/g, and tensile fracture strain of 5.7%. It showed that a large number of slip bands and dislocation bands are the main deformation products at 298 K, leading to excellent ductility. In comparison, high dislocation density was found between the slip bands in the samples deformed at 873 K, which can effectively hinder the motion of dislocations, resulting in strain hardening and the increase in strength. This work can provide a route for the design and fabrication of high-performance lightweight alloys, which would be beneficial for engineering applications.