CuZnAl shape memory alloy samples were irradiated by 1.7 MeV electrons under the parent and martensite phase, respectively. The transformation temperatures were measured by differential scanning calorimetry (DSC). The effect of electron irradiation on the ordering degree was studied by X-ray diffraction (XRD) by estimating the spacing difference (△d) of some selected pairs of diffraction planes. The damage accumulation was determined by positron annihilation technology (PAT). The results showed that irradiation under the parent phase produced no change in the transformation temperatures. The reverse martensite transformation temperatures (As and Af) shift to higher temperature of samples and increase with increasing electron doses when irradiation was performed under the martensite phase. The XRD results showed irradiation under the parent phase produces little change in △d, but △d decreased for the CuZnAl samples irradiated under the martensite phase, this implied that the ordering degree of the martensite decreased after the irradiation under the martensite phase. The PAT results showed that the concentration of vacancy clusters increased after irradiation. It is thought that the martensite stabilization is related to the decreasing of ordering degree in the martensite state.

Ti-50.6at.%Ni shape memory alloy specimens were irradiated in the parent phase using a tandem accelerator by 18 MeV protons at a dose rate of 4.27

A model is proposed for the calculation of the irradiation induced changes of the martensitic transformation temperatures of shape memory alloys. It considers the transition temperatures being determined by a chemical and a non-chemical term in the Gibbs free energy that can be affected by the irradiation induced changes of the vacancy density and the chemical ordering of the crystal structures. Numerical simulations for TiNi SMAs have shown that upon irradiation the austenite finish temperature Af can be raised slightly at the beginning stage. After that, both Af and the martensite start temperature Ms will decrease strongly and reach some stable values after extensive irradiations. Both the dose rate and the temperature of irradiations will affect the changes of Ms and Af. According to the simulation, the increase of Af at the beginning of irradiations is resulted from the irradiation induced point defect production that increases mainly the non-chemical term in the Gibbs free energy change of the martensitic transformation. The irradiation induced chemical disordering reduces both the chemical and non-chemical terms in the Gibbs free energy change and leads to the strong decreases of Ms and Af.

TiNi shape memory alloy samples annealed at 673K for 1h were irradiated within R-phase by 1.7-MeV electrons with different doses. The two-step martensitic transformation temperatures were measured by differential scanning calorimeter. The results indicated that the temperature M of the onset of R-phase-to-martensite transformation decreased with increasing electron dose. The electron irradiation had s a slight effect on the other transformation temperatures. The second lifetime of positrons determined by positron annihilation technology were lowered with increment of the irradiated dose. Relaxation of the elastic stress fields around the Ti Ni precipitates was the cause of 3 4 the observed change of the transformation characteristics because of the migration and accumulation of irradiation-induced point defects.

TiNiCu shape memory alloy samples were irradiated by 1.7MeV electrons below the martensite finish temperature Mf. The transformation temperatures and the latent heat of phase transformation were measured by differential scanning calorimeter. The damage accumulation was determined by positron annihilation technology. The results indicated that the austenite transformation temperatures were raised, and the hysteresis was increased by the irradiation. The electron irradiation had a slight effect on Mf, and no detectable effect on the martensitic transformation start temperature Ms. The second lifetime of positrons were increased by the electron irradiation indicating the increase in the size and amount of vacancy clusters, which contributed to the observed change of the transformation characteristics.