Effect of pre-deformation on the transformation temperatures of TiNi shape-memory alloys

The predeformation in the rang from 1% to 13.6% (fracture) were performed in a TiNi alloy. It was observed that the reverse martensitic transformation temperature of the deformed TiNi alloy rises linearly with the increase of deformation up to 8%, and then, the tendency is accelerated due to the plastic deformation. And more, the latent heat almost keeps unchanged till 8% deformation, and then has a slight increase with further deformation. Our results suggest that the increase of the reverse transformation temperature is attributed to the change of the microstructure caused by deformation. The amount of the prefer-red variants adds with the increase of the deformation, which results in a stability of the martensitic structure owing to a lower free energy of the singe variant compared with the mixed ones.