X-ray diffraction analysis of phase transformations of a TiNi memory alloywith equiatomic form as a function of the deformation rate and heat treatment

The influence of the deformation rate and of the heat treatment on R, marte nsitic and austenitic transformations and their volume fractions in equi-at omic TiNi shape memory alloy (SMA) wires, annealed at different temperature s has been investigated by X-ray diffraction. At 450 degrees C and 510 degr ees C, the volume fraction of martensite decreases as the deformation rate increases. This behavior is different from that observed at 570 degrees C a nd 600 degrees C, which is attributed to recrystallization. At 450 degrees C and 510 degrees C, for the austenite phase, the volume fraction of austen ite increases with the increase deformation rate. The behavior is different for a deformation over 10% and at temperature over 510 degrees C. Unlike t he volume fractions of martensite and austenite, the volume fraction of R-p hase increases as the deformation rate increases and the heat treatment tem perature decreases. This phenomon is attributed to the existence of residua l internal stresses inside the SMA.