Effects of pre-deformation and subsequent low-temperature annealing on transformation, mechanical properties and shape memory behavior of a Ti-rich TiNi alloy

Abstract

Effects of pre-deformation in the martensitic state and subsequent low-temperature annealing on the phase transformation, tensile properties and shape memory performance of a Ti-49.8 at.% Ni alloy were investigated in order to improve mechanical and memory properties of the alloy. The results show that water quenching from 850 degrees C and subsequent annealing do not induce Ti-rich precipitates in the alloy. Transformation from parent to R-phase appears on cooling for alloys annealed at 350-500 degrees C after pre-deformed to the strain of as high as 19.0%, and the transformation temperature and rate from parent to R-phase are not affected by pre-deformation, but M(s) and M(f) reduce with increasing pre-deformation strain, and the volume fraction of R-phase increases in the microstructure of alloys annealed at low temperature after pre-deformation to higher strain. Tensile and memory properties of the Ti-49.8 at.% Ni alloy can be improved by appropriate pre-deformation (more than 27.8% strain) in the martensitic state and subsequent low-temperature annealing (at 400 degrees C).