Dilatometric Study of the Precipitation Kinetics in Cu-Al-Ni Shape Memory Alloys

Abstract
The maximum working temperature in CuAlNi shape memory alloys is limited by the precipitation of the stable phases that damages the good thermomechanical behaviour during the martensitic transformation. In this paper, the precipitation kinetics of the stable phases inside the metastable β phase have been studied by quenching dilatometry in a wide range of temperatures. The different phases have been characterised by scanning electronic microscopy and X-ray diffraction. Moreover, the precipitation kinetics have been analysed using a double Jhonson-Mhell-Avrami equation. The extrapolation of the obtained characteristic parameters allows us to predict the behaviour of the alloy at lower temperatures. Finally, the TTT curve has been obtained for both the primary precipitation and the eutectoid decomposition.