The effects of gamma-irradiation on transformation temperatures of NiTi shape memory alloy

The influence of gamma-irradiation on transformation temperatures of NiTi shape memory alloy was investigated by differential scanning calorimetry. The austenite transformation temperatures shifted to higher temperatures after gamma-irradiation, whereas the martensite transformation temperatures shifted to lower temperatures. The equilibrium temperature, To between the martensitic and parent phases increases with increasing irradiation dose. The Gibbs free energy values, ΔGP→M for the transformation from parent phase to martensite phase were determined and the value of ΔGP→M increases with increasing irradiation dose up to 60 kGy. The mechanism of gamma-irradiation inducing the martensitic transformation is due to the displacements of atoms from their lattice sites produced by the accelerated gamma particles.