Precipitation sequence during ageing in β1 phase of Cu–Al–Ni shape memory alloy

The shape memory alloys based on the ternary system Cu–Al–Ni are able to produce a memory effect at high temperatures. However, if the material undergoes an accidental overheating, a transformation process leads to progressive loss of its characteristics. In this study, the effect of ageing on the metastable β1 (austenite) phase of a Cu–13.3 %Al–4 %Ni shape memory alloy was investigated. In addition, the effects of heating rate between 450 and 580 °C on the structural transformations of austenite after cooling to room temperature were studied. Observation by transmission electron microscopy of the structure that has undergone an isothermal ageing shows that the precipitation process depends on the maximum ageing temperature. Furthermore, calorimetric analysis shows that precipitates dissolution is possible when rapid heating between 450 and 580 °C. This behaviour is observed on the cooling diagram which shows a martensitic transformation.