Improving strength-ductility synergy of TiNbVTa refractory high-entropy alloys at room temperature by Cr microalloying

Abstract

Due to their excellent mechanical performance at elevated temperatures, TiNbVTa-based alloys have emerged as a focal point of research within the field of refractory high-entropy alloys (RHEAs). However, the intrinsic trade-off between strength and ductility in TiNbVTa alloys continues to limit their further development for ambient-temperature applications. In this study, a novel microalloying strategy is proposed by introducing chromium (Cr) to promote the formation of substitutional solid solutions, thereby enhancing the room-temperature mechanical properties of TiNbVTa-based RHEAs. To validate this approach, a series of (TiNbVTa)_100-xCr_x (x = 0, 0.35, and 0.7 at.%) RHEAs was systematically designed and synthesized. The results revealed that all the investigated alloys possessed a single body-centred cubic (BCC) phase structure. As the Cr content increased from 0 to 0.7 at.%, the ultimate tensile strength, yield strength, and elongation of the (TiNbVTa)_100-xCr_x alloys initially increased, followed by a subsequent decline. Notably, the (TiNbVTa)_99.65Cr_0.35 alloy exhibited exceptional room temperature mechanical performance, achieving a tensile yield strength of 903 ± 22 MPa and an elongation of 18.7 ± 2.6 %, both of which surpass previously reported values for TiNbVTa-based RHEAs. The enhancement in mechanical properties induced by Cr microalloying was ascribed to the synergistic contributions of the synergistic hindrance of dislocation motion by SROs and the lattice distortion field induced by Cr addition, impeded dislocation motion through the formation of dislocation rings, and the promotion of dislocation proliferation. Furthermore, this study introduces microalloying as an effective strategy for concurrently improving both the strength and ductility of RHEAs.