Dual enhancement in strength and ductility of Ti-V-Zr medium entropy alloy by fracture mode transformation via a heterogeneous structure

Abstract

The formation of a homogeneous body center cubic (BCC) solid solution and short-range clustering (SRC) allow refractory multi-principal elements alloys to reach incredibly high yield strengths, but their uses are severely constrained by their inherent brittleness. In this study, Ti-V-Zr medium entropy alloys with SRC are designed and prepared, and the heterogeneous grain structures (HGS) with multiphase are formed. By tunning microstructure, movable dislocations provide deformation ability, since shear beads formation is depressed. The strength and ductility of Ti40Zr60-xVx alloys are enhanced by the increasing proportion of V. Ti40Zr15V45 alloy achieves a high yield tension strength of 1067 MPa and ductility of >7 % at room temperature. With a 1793 MPa compressive strength, it outperforms other BCC alloys with a homogeneous structure. Thermodynamic stability of phases indexed by parameters tends to form heterogeneous microstructure in grain scale, which realizes dual enhancement of strength and ductility by altering the ratio of phases. Dislocation reactions, which are also visible in SRC, result in shear band fractures with dimples on the cleavage plane surfaces. The <001> immovable dislocation is formed in the SRC structure and provides extra strengthening. The formation process model has been developed and validated. The model for the formation process has been built and proven.