Effect of thermal cycling on the R-phase and martensitic transformations in a Ti-rich NiTi alloy

The effect of thermal cycling on transformation temperature was studied on a Ti-rich NiTi alloy. The study was carried out by determining the electrical resistance, the internal friction, and the elastic modulus vs temperature. This study shows that the martensite microstructure is modified by the successive cycling transformation. In addition, we established that both the martensite internal friction and the transition peak are sensitive to the transient effect (the vibration frequency lies around 300 Hz). But the major results concern the behavior associated with the R phase occurrence and its evolution. We have stated that the premartensitic phase becomes stable following the diminishment of the beginning of the martensite formation (Ms). Interrupted cooling has also shown that, contrary to the martensite, the R phase exhibits no hysteretic behavior.