Martensitic Transformation and Shape Memory Effect in TiNi-Based Alloys during Neutron Irradiation

Abstract

The chapter is devoted to a study of the influence of neutron irradiation on the martensitic transformations and shape memory effects in TiNi-based shape memory alloys. Irradiation of the samples was carried out in the low-temperature helium loop of a WWR-M fusion reactor at Petersburg Nuclear Physics Institute in Gatchina (Russia). The experimental data showed that the variation in transformation temperatures depended on the irradiation temperature. The main factors influencing the variation in transformation temperatures during irradiation were disordering of the solid solution at low temperatures, radiation ordering at high temperatures, and thermally activated annealing of radiation damage. All of these mechanisms were taken into account in the differential equation given in the present work for description of the transformation temperature variation during irradiation at different temperatures. It was found that irradiation up to a fluence of 7⋅10 18 cm -2 did not suppress the transformation plasticity and shape memory effects in TiNi alloy in spite of the variation in transformation temperatures. It was observed that the shape memory effect may be initiated by irradiation up to a fluence of 5⋅10 20 cm -2 at a constant temperature (under isothermal conditions) due to a decrease in transformation temperatures.

Particle radiation effects on shape memory alloy couplers for ultra-high vacuum sealing: a preliminary study

“…Amorphization of neutron irradiated NiTi samples was also confirmed by TEM observation in [20]; this study reports changes in the TTs and mechanical properties similar to those of previous researches, pointing out that no significant microstructural changes occur in NiTi neutron irradiated with a fluence lower than of 1.3 × 10 18 cm −2 (E>1 MeV). More lately, it was found that neutron irradiation up to a fluence of 7 × 10 18 cm −2 (E>1 MeV) do not suppress the shape memory effects in NiTi alloys despite an evident TTs variation [13]. Furthermore, analogous effects were also reported in few other studies investigating gamma and proton irradiation effects, i.e.…”

“…The major damage produced by fast neutron irradiation in metals is mainly related to atomic displacement cascades creating stable Frenkel pairs [12]. Therefore, when the ordered crystalline structure of SMA is irradiated, microstructural changes could occur, depending on particle types, energies, flux, integral fluence as well as irradiation temperature [12,13]. These changes could lead to a degree of amorphization and therefore, to possible modification in the phase transition mechanisms.…”

“…These changes could lead to a degree of amorphization and therefore, to possible modification in the phase transition mechanisms. Most of the studies in literature refer to NiTi alloys irradiated with fast neutrons (energy E>1 MeV) to fluences ranging from 10 16 to 10 21 cm −2 [9][10][11][13][14][15][16][17][18][19][20]. In particular, three different types of NiTi alloys were analyzed by Hoshiya et al [15]; electrical resistance tests were carried out on neutron-irradiated specimens.…”