Investigation of nucleation and propagation of phase transitions in TiNi SMA

The attention of the present paper is focused on the aid provided by infrared thermography, for spectacular investigation of nucleation and further development of the stress induced phase transitions in TiNi shape memory alloy. This is a qualitative analysis aimed to verify the feasibility of further study in the application of IR for studying change phenomena. To this end, the material stress-strain curves, obtained during tension test with various strain rates, were completed by the temperature characteristics. The temperature distributions on the specimen's surface were determined by using an infrared camera. A heterogeneous temperature distribution, related to the nucleation and development of the new martensite phase, were registered and analyzed. A significant temperature increase, up to 30 K was registered during the martensite transformation. Similar effects of the heterogeneous temperature distribution were observed during unloading, while the reverse transformation, austenite into martensite, tooks place. The reverse transformation was accompanied, in turn, by a temperature decrease, of up to 10 K.