On the effect of room temperature ageing of Ni-rich Ni-Ti alloys

We show that the cubic-monoclinic martensitic transformation (B2-B19′) in Ni-rich Ni-Ti alloys is strongly affected by room temperature exposure after quenching from 1270 K, presumably due to the initial stage of precipitation: transformation temperatures strongly decrease, the hysteresis increases and in the Ni50.8Ti49.2 alloy the transformation gets arrested. The suppression of the B2-B19′ transformation is not preceded by the cubic-trigonal (R-phase) transition, indicating that nm-size precipitates or their nuclei do not serve as nucleation sites for the R-phase.