Restoration phenomena of Ti-Ni shape memory alloys in a neutron irradiation environment

Transformation properties and deformation behavior of Ti-Ni shape memory alloys, which were neutron-irradiated at 323 and 520 K with a maximum fluence of 14 x 1025 and subsequently post-annealed at 473, 525 and 573 K, were measured by electrical resistance measurements and tensile tests. At an irradiation temperature of 323 K, abrupt changes in Ms temperatures and stress-strain curves of specimens were observed at a dose of over 10-2 dpa. Irradiation alterations were annihilated by post-irradiation annealing at temperatures above 523 K. On the other hand, 520 K irradiations brought about quite a few changes in those properties regardless of the magnitudes of displacement. The irradiated state of this alloy can be represented by two conflicting processes; ordering and disordering, which depends on temperature, displacement and displacement rate. The key temperature of that state is 520 K, at which the ordering becomes predominant over disordering and brings about the occurrence of a restoration phenomena. (orig.)