An ambient ductile TiHfVNbTa refractory high-entropy alloy: Cold rolling, mechanical properties, lattice distortion, and first-principles prediction

Abstract

Refractory high-entropy alloys (RHEAs) have promising applications in industry due to their outstanding high-temperature properties, but most of them are brittle and poorly plastic formability at ambient temperature. Developing new ambient ductile RHEAs is a challenge in current materials research. In this work, an ambient ductility TiHfVNbTa alloy was prepared, and its microstructure, mechanical properties, phase stability, lattice distortion, and basic physical properties were investigated by combing experiments and density functional theory (DFT) calculations. The obtained results show that TiHfVNbTa alloy has excellent cold-rolled formability with >84% thickness reduction, no crack generation, and ultimate tensile strain up to >12% at ambient temperature. Besides, the tensile yield strength (hardness) of the alloy increases from 997 MPa (363 HV) in the annealed state to 1340 MPa (453 HV) in the 84% cold-rolled state, displaying work-hardening behavior. The TiHfVNbTa alloy has a single-phase solid solution body-centered cubic (BCC) structure, and no structural transformation occurs during rolling and tension, implying its good phase stability. Notably, the TiHfVNbTa alloy exhibits a higher specific yield stress and ductility compared to most RHEAs. DFT results reveal that the high strength is mainly contributed by severe lattice distortion. Hf and V elements are the major sources of lattice distortion. In addition, the physical properties such as metallic bonding, anisotropy and electronic structure are also analyzed based DFT calculations. The obtained results not only help to understand the material properties of TiHfVNbTa alloy, but also provide design guidelines for novel ductile RHEAs.