Abstract
The stress-induced phase transformation characteristics of unirradiated and proton beam irradiated NiTi alloy were investigated at different tests temperatures. The wire-shaped NiTi specimens were irradiated by 2 MeV proton beam for 30 min at room temperature to a flux of 10(19) protons/m(2) s. Engineering stress-strain (S-S) curves of both unirradiated and irradiated specimens were obtained using a materials testing machine at 25, 50, 75 and 100 degrees C. The results indicate a single-stage phase transformation from austenite to martensite (B2-B19') in unirraidated specimens at all the test temperatures. In contrast, in the case of the irradiated specimens, a two-stage austenite-rhombohedral-martensite (B2-R-B19') phase transformation is observed at 25 and 50 degrees C. The B2-R-B19' phase transformation, however, is found to change into B2-B19' transformation at 75 and 100 degrees C. The stress required to initiate the B19' phase transformation (sigma(MS)) and the plateau range are found to be lower in irradiated specimens compared with those of the unirradiated specimens. The results obtained are discussed on the basis of the formation of Ni4Ti3 precipitates in irradiated specimens and their consequences on the phase transformations.