Effect of annealing temperature on the microstructure and superelasticity of Ti-19Zr-10Nb-1Fe alloy

The effects of annealing temperature on the microstructure, mechanical properties and superelasticity of Ti-19Zr-10Nb-1Fe alloys were investigated. The as-rolled alloy was annealed at temperatures between 823K and 1173K. The alloy annealed at 823K consisted of major β and partial α phases. Equiaxed β grains with nanoscale ω precipitates were observed in the alloys annealed above 873K. The α/β transus temperature and recrystallization temperature of Ti-19Zr-10Nb-1Fe alloy were both determined to be between 823K and 873K. The alloy annealed at 823K exhibits a higher ultimate tensile strengthen and a lower fracture strain than other alloys, due to the residual work hardening, and the coarse and non-uniformly distributed α precipitates. Ti-19Zr-10Nb-1Fe alloys annealed at 873K and 973K exhibited superelasticity in tension due to the stress induced martensitic transformation. However, no obvious superelasticity can be observed during the tensile deformation of the alloys annealed at 823K or 1173K, implying the suppression of stress-induced martensite transformation by high-density dislocations or increased β grain size, respectively. The alloy annealed at 873K exhibited a good combination of large elongation of ~24.8%, low Young's modulus of ~58GPa, high ultimate tensile stress of ~703MPa and the maximum superelasticity of ~3.7%.