Ti-Ni系形状記憶合金の中性子照射損傷の回復

Abstract

Transformation properties and deformation behavior of Ti-Ni shape memory alloys which were irradiated at 323 and 520 K up to a maximum fast neutron fluence of 1025 m−2 and subsequently annealed above 523 K, were examined by electrical resistance measurements and tensile tests. When irradiation was performed at 323 K, Ms temperature of irradiated specimens abruptly decreased at a dose over 10−2 dpa. This shows that the irradiation has a great influence on transformation properties of specimens. After post-irradiation annealing above 523 K, the Ms temperature of specimens which were irradiated with a dose of 10−1 dpa, increased to that of unirradiated ones. When irradiation was performed at 520 K, the decrease in Ms temperature was negligibly small regardless of the magnitude of damage. It is clear that at irradiation temperature of 520 K the irradition has no influence on transformation properties of Ti-Ni alloys.In the Ti-Ni alloys two conflicting processes take place during irradiation: disordering and ordering. The migration of vacancies is enhanced by thermal activation and ordering becomes predominant over the disordering and restoration phenomena occur. The phenomena can be described as a function of temperature, displacement and displacement rate by the theory of order-disorder transformation under irradiation. It is confirmed that the threshold temperature at whith the restoration phenomena take place is about 520 K.