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 studie d on a Ti-rich NiTi alloy. The study was carried out by determining th e electrical resistance, the internal friction, and the elastic modulu s 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 transit ion peak are sensitive to the transient effect (the vibration frequenc y lies around 300 Hz). But the major results concern the behavior asso ciated with the R phase occurrence and its evolution. We have stated t hat the premartensitic phase becomes stable following the diminishment of the beginning of the martensite formation (M-s). Interrupted cooli ng has also shown that, contrary to the martensite, the R phase exhibi ts no hysteretic behavior.