Effect Of Electron Irradiation On The Transformation Characteristics Of Shape Memory Alloys

Coupling devices and actuators using shape memory alloys (SMAs) are attracting interest for applications in the fields of nuclear engineering and space technology on account of their shape memory effect and Pseudoelasticity. In view of the potential change of their phase transformation characteristics in irradiation,it is necessary to know the effect of irradiation on the shape memory behavior of the alloy.In this paper,Specimens of CuZnAl,NiTi and NiTiCu shape memory alloys were irradiated with an energy of 1.7MeV electron over different dose after respective heat treatments. Then,the irradiation effect on the transformation temperatures,the latent heat of phase transformation,the defect production and the microstructure of the specimens have been studied by means of differential scanning calorimeter (DSC),positron annihilation technology (PAT),X-ray diffraction (XRD),scan electron microscope (SEM) and transmission electron microscope (TEM). Summing up the experiment results and the theories of the irradiation effecU the thermodynamics of phase transformation,the influencing mechanism of the electron irradiation to the SMAs was discussed.Now the experiment results are summarized as follows:The phase transformation of the CuZnAl,NiTi and NiTiCu SMAs finally haven't gone to the amorphization phase after low energy electron irradiation,but the transformation temperatures were altered. The martensite of CuZnAl alloy was stabilized by the irradiation in the sense that the reverse transformation temperature(As) was higher than before. However,the start temperature of martensitic transformation (AQ showed variety because of the irradiation states:the Ms of the specimen irradiated in high temperature (parent phase) increased and that,the Ms of the specimen irradiated in room temperature (martensitic phase) decreased. The As increased and Ms decreased of the NiTi alloy,but the R-phase transformation has little been changed. For the NiTiCu alloy,the irradiation raised the As,whereas had little influence to the Ms.The mechanism of the irradiation effect to the SMAs might be due to that the point defects induced by electron irradiation make the lattice distortion of martensitic phase and raise the defect concentration. The defects would congregate and migrate to the exiting twin boundaries of martensite,affect the strain enery of the martensitic variants and change the disordering of the crystallographic structure. The extend of irradiation effect to the three kinds of the SMAs are different,and it is related to their displacement energy vacancy forming-energy and vacancy moving-energy.The transformation behavior of the SMAs is tied up to the martensitic phase transformation. On the base of the former theory work,using developed thermodynamical modeling of the martensitic transformation,the shift of the interior energy is elementarily analyzed.