INFLUENCE OF THERMOMECHANICAL TREATMENTS ON CHARACTERISTIC OF CuAlNi SHAPE MEMORY ALLOY

Systematic investigations were promoted on the role of quenching, hot extrusion and ausforming on the phase transformation behavior in Cu-12.88 wt%A1-3.98 wt% Ni. The fracture behavior, the microstructure evolution and the martensitic transformation have been studied by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The martensitic transformation and the shape reversibility in Cu-Al-Ni shape memory alloy are strongly depended on quenching and thermomechanical treatments parameters. The very high elastic anisotropy and large grain size of these alloy contribute to the intergranular brittleness. The fracture surfaces indicate involvement not only of the high stress concentration around the corners of the grain boundaries but also occurrence of precipitation. Their transformation ductility improvement, have been achieved handling the grain size by ausforming. It was found that the variation of the grain size is highly sensitive to the degree of deformation and the homogenizing temperature. The plastic deformation of austenite leads to grain refinement, increase the mechanical properties and uplift martensitic temperature without suppression of transformation cycles up to 37% deformation degree. In addition a particular as bamboo-grain microstructure was achieved in a narrow range of deformation degree (close to 15%) via rolling at 980 inverted perpendicular C followed by fast cooling. The influence on martensitic transformation is discussed in this specific case of minimizing the area of crystalline grain boundaries.