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.

The structural mechanisms of the hardening of a Ti-2Al-2.5Zr alloy by 75 keV nitrogen ion implantation with doses of 3310 and 17 2 8310 N/cm is investigated. The surface characterization of samples was studied by XPS, XRD and Vickers hardness tests. The results of XPS and XRD analysis show that TiN is formed in the surface region. Nitrogen implantation increases the surface hardness up to 340 17 17 2 and 260% for doses of 8310 and 3310N/cm, respectively, due to formation of TiN and irradiation-enhanced hardening.

The effect of irradiation on the martensitic transformation of TiNi shape memory alloys was studied by transmission electron microscopy (TEM) with in situ observation and differential scanning calorimeter (DSC). The results of TEM and DSC measurements show that the microstructure of samples is R phase at room temperature. Electron irradiations were carried out using several different TEM with accelerating voltages of 200, 300, 400 and 1000kV. Also the accelerating voltage in the same TEM was changed to investigate the critical voltage for the effect of irradiation on phase transformation. It was found that a phase transformation occurred under electron irradiation above 350kV, but never appeared at 340kV or lower accelerating voltage. Such phase transformation took place in a few seconds of irradiation and was independent of atom diffusion. The mechanism of electron-irradiation-induced the martensitic transformation is due to displacements of atoms from their lattice sites produced by the acceleratedelectrons. The critical displacement energy of TiNi SMAs is B18 eV from the results.

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.

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.