Influence of irreversible plastic deformation on the martensitic transformation and shape memory effect in TiNi alloy

The focus of this study is the influence of irreversible plastic deformation on the martensitic transformation and strain recovery after deformation of the specimen in the martensitic state. Both strain and electrical resistance in TiNi alloy have been measured simultaneously on heating and cooling of the sample which has been preliminarily deformed first in austenite (at 600 K) and then in martensite (at 290 K). A decrease of the alloy capacity for strain recovery and the change of the martensitic transformation sequence with an increase of the plastic strain have been found. Besides, the experimental data have shown that the electrical resistance varies with a hysteresis on heating and cooling of the sample deformed to 60%. This hysteresis is observed in a wide temperature interval and does not disappear with thermocycles. One can suppose that the internal oriented stresses may be the main cause of the observed phenomena.