Effect of neutron irradiation on the transformation and mechanical properties in Ti-Ni shape memory alloys

Transformation characteristics, deformation behaviour and hardness properties of near equi-atomic Ti-Ni shape memory alloys irradiated at 323 K by neutrons to the fast neutron fluence of 8 x 1023 m-2 have been studied by remote-controlled electrical resistance measurement and tensile and hardness tests. The MS temperature of a Ti-Ni alloy seemed to decrease to about 100 K by the irradiation and the amount of the decrease in MS was more than 200 K. On the other hand, the TR temperature (the formation temperature of an intermediate phase (R-phase)) shifted to 1∼7 K lower than that of the unirradiated Ti-Ni alloy. The fracture stresses and fracture strains (including elastic strain) at room temperature were in the range of 1300 to 1700 MPa and 6 to 8%, respectively. Unusual elastic behaviour with a recoverable strain of 5% was found in tensile testing. The atomic replacements formed by neutrons may bring about radiation induced disordering and have an influence on transformation properties and deformation behaviour of those alloys. On the other hand, the restoration of the damage, which follows radiation-induced ordering, can occur on post-irradiation annealings at 523 K for more than 600 s. (author)