Using dilatometry to study martensitic stabilization and recrystallization kinetics in a severely deformed NiTi alloy

A martensitic NiTi alloy was separately processed by equal-channel angular pressing, repetitive corrugation and straightening by rolling and cold rolling. Measurements by dilatometry revealed a significant increase in the austenitic phase transformation temperature and martensitic stabilization after severe plastic deformation. The release of an excess volume upon recrystallization of the deformed NiTi alloy was measured using a high-precision difference-dilatometer employing non-isothermal and isothermal procedures. The kinetics of the recrystallization process was analyzed according to the Johnson-Mehl-Avrami-Kolmogorov theory and the average effective Avrami exponent was estimated as n a parts per thousand 1. It is concluded that the recrystallization behavior is essentially similar for all three processing modes.