Microstructure evolution of a novel low-density Ti–Cr–Nb–V refractory high entropy alloy during cold rolling and subsequent annealing

Abstract

Refractory high entropy alloys represent a new class of metallic alloys attractive for high-temperature applications. However, most of the developed alloys have either low ductility at room temperature or high density. In this work, we report structure and mechanical properties of a novel non-equiatomic Ti1.89CrNbV0.56 alloy produced by vacuum arc melting. The density of the alloy was 6.17 g/cm3. In the as-cast condition, the alloy had a single-phase bcc structure enabling room temperature deformation in compression to ε>50% or cold-rolling to a thickness strain of 80%. Rolling resulted in the formation of a dislocation substructure and development of kink and shear bands. Meanwhile, microhardness measurements have revealed only a moderate increase from 396 HV in the as-cast condition to 454–469 HV after 40–80% rolling. After 80% cold rolling the alloy had yield strength of 1020 MPa, ultimate tensile strength of 1535 MPa, and elongation to fracture of 3.5%. The cold rolled alloy was annealed at 800, 1000 or 1200 °C for 1–100 h. Microstructural response to the annealing strongly depended on temperature. Annealing at 800 °C mostly resulted in Cr-rich fcc (C15) Laves phase particles precipitation. Annealing at 1000 °C led to the bcc matrix recrystallization along with the precipitation of the Laves phase particles, thereby producing a fine duplex microstructure. Finally, annealing at 1200 °C resulted in a coarse-grained recrystallized single-phase bcc microstructure. Microhardness of the alloy lowered with an increase in the annealing temperature while the annealing time had a small effect on hardness.