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 823 K and 1173 K. The alloy annealed at 823 K consisted of major β and partial α phases. Equiaxed β grains with nanoscale ω precipitates were observed in the alloys annealed above 873 K. The α/β transus temperature and recrystallization temperature of Ti-19Zr-10Nb-1Fe alloy were both determined to be between 823 K and 873 K. The alloy annealed at 823 K 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 873 K and 973 K 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 823 K or 1173 K, implying the suppression of stress-induced martensite transformation by high-density dislocations or increased β grain size, respectively. The alloy annealed at 873 K exhibited a good combination of large elongation of ~24.8%, low Young's modulus of ~58 GPa, high ultimate tensile stress of ~703 MPa and the maximum superelasticity of ~3.7%.