Effect of 18 MeV proton irradiation on the R-phase transformation in TiNi shape memory alloys

Ti-50.6at.%Ni shape memory alloy specimens were irradiated in the parent phase using a tandem accelerator by 18 MeV protons at a dose rate of 4.27 x 10(9) cm(-2) s(-1) for 1 h and 10 h, respectively. The total doses were 1.5 x 10(13) and 1.5 x 10(14) H+/cm(2). Microstructures and phase transformation characteristics of the specimens before and after irradiations were evaluated by transmission electron microscopy and differential scanning calorimetry. There is no observable change of the microstructures after the irradiation. The parent phase (austenitic phase) was stabilized by the irradiation, since the R-phase transformation start temperature R-s and the reverse martensitic transformation finish temperature A(f) had decreased with increasing proton dose, about 6 K for R-s and 13 K for A(f) at a dose of 1.5 x 10(14) H+/cm(2). A(s) and R-f were not affected by the proton irradiation. The variation of the transformation temperatures was assigned to local stress fields and changes in the degree of the lattice order produced by the proton irradiation. (C) 2003 Elsevier B.V. All rights reserved.