Microstructures evolution and phase transformation behaviors of Ni-rich TiNi shape memory alloys after equal channel angular extrusion

Abstract

Ni-rich TiNi shape memory alloys were subjected to the effect of equal channel angular extrusion (ECAE) processes at 773 K by Bc path. The effects of ECAE processes on microstructures evolution and phase transformation behaviors were investigated. The initial 60–80 μm equiaxed coarse grains of samples were elongated along the shearing force direction of ECAE and refined to 300–400 nm after eight passes ECAE. The R phase transformation of Ni-rich TiNi shape memory alloys was stimulated by ECAE processes within a larger temperature range. The martensite transformation peak temperature (Mp) dropped in previous 1–3 ECAE treatments, but the dropped Mp increased gradually with the increase of ECAE processes. Ti 3Ni 4 phase was observed in the regions with high density of dislocations after ECAE treatment. Reasons for microstructures evolution and phase transformation changes were also discussed.