Superior cryogenic strength and ductility in VNbTa body-centered cubic medium-entropy alloys

In this study, the deformation behavior of an equiatomic VNbTa medium-entropy alloy with a BCC single phase is studied by tensile tests at cryogenic temperatures. The results show that the alloy presents a strong strain hardening capability, which leads to a high ultimate tensile strength of 1930 MPa while maintaining a high fracture elongation of ∼27%, without a ductile to brittle transition. The excellent cryogenic temperature mechanical properties of the present alloy are attributed to the cooperative of {112}〈111〉 deformation twins, dislocation interaction, and entanglement caused by the continuing cross-slip of dislocation. The localized severe lattice distortions caused by the large atomic size misfit of elements among Nb, Ta and V play a major role in the cross-slip of dislocation.