Pre-martensitic phenomenon in NiTi studied by positron lifetime spectroscopy

The pre-martensitic phenomenon in Ni,,Ti,, has been studied by positron lifetime spectroscopy which is quite sensitive to electronic-structural changes of matter. In this work we have found an anomalous positron lifetime change above martensitic transformation temperature of Ni51Ti49: positron lifetime increases anomalously with decreasing temperature even at temperatures 100 degrees higher than the M-s temperature of the alloy. Almost the same change in positron lifetime also has been observed on the heating run with little hysteresis, which clearly indicates that the observed pre-martensitic change of positron lifetime is due to the intrinsic electronic-structural change of NiTi alloys which causes so-called pre-martensitic phenomena.