Cyclic Deformation of TiNi Shape Memory Alloy under Various Thermomechanical Paths

The cyclic deformation behaviour of TiNi shape memory alloy under various thermomechanical paths was investigated experimentally. The main results are sunlmarized as follows. For the stress-induced martensitic transformation and the reverse transformation under cyclic loading-unloading or heating-cooling, the transformation stress decreases and the transformation temperature rises with an increase in the number of cycles. The amount of variation in the stress and the temperature for the stress-induced martensitic transformation is larger than that for the reverse transformation. These variations are significant if the deformation is repeated in the region of high stress. The nonrecoverable strain which appears with cyclic deformation is large for high stress. The amount of variation in the transformation stress, the transformation temperature and the nonrecoverable strain is large in the early cycles but decreases after a certain number of cycles.