Investigation of the heat treatment effects on the CuAlNi shape memory alloys

Metastable P-phases of copper-based shape memory alloys are very sensitive to thermal treatments before and after the transformation. These thermal treatments may cause important changes on morphologic properties and transformation temperatures or on the other transformation parameters of the alloys. In this study, thermal treatments effects and aging under mechanically applied stress on two Cu-ll%Al-3.82%Ni and Cu-ll%Al-3.38%Ni (in weight) have been investigated by using differantial scanning calorimetry (DSC) technique and metallographic observations. Electrical resistance, magnetic and thermal conductivitiy properties of samples have also been examined. It was observed that the transformation temperatures of the samples which were cooled in different parts apart from the P-phases area changed. However in enthalpy and entropy change, entropy change in martensite phase was observed to be higher than the entropy change of main phase. The magnetic measurements showed that the samples have paramagnetic property. From the various heating rate measurments, it was observed that the reverse transformation temperatures were increased by the increase of the heating rate. The grain structures were observed; plate martensites, v-type martensite structures, precipitation phases were found. Key words: CuAINi alloys, shape memory effect, transformation temperatures, enthalpy and entropy change, stress.