The investigation of pressure effect on ageing phenomena of CuAlNi shape memory alloy

Shape memory alloys (SMA) are smart materials that work by transforming between two crystal structures, austenite, and martensite phases. These phases are determined by the temperature and internal stresses of the material. Shape memory alloys can return to their pre-deformation shape and dimensions with heat treatment applied after plastic deformation. Shape memory alloys are related to martensitic transformation, also called diffusionless transformation between austenite phase and martensite phase, which has functional behavior based on unidirectional and bidirectional shape memory effect, superelasticity, and pseudo-elastic effects. Due to the low cost of Cu-based shape memory alloys, they have been the focus of attention of researchers and attracted attention from a technological point of view. In this study, Cu-13.5Al-4Ni (wt%) shape memory alloy was used. Alloy samples were aged under the constant pressure of 558 Mpa at different times (0; 5 min; 15 min; 30 min; 45 min; 60 min.) and also at equal times under different pressures (0; 186 Mpa; 372 Mpa; 558 Mpa; 745 Mpa; 930 MPa). Differential scanning calorimetry (DSC) was used to determine the transformation temperatures and thermodynamic parameters of aged Cu-13.5Al-4Ni shape memory alloy samples. Microstructural investigations of aged samples were made by X-ray diffraction and optical microscope observations. It is microhardness measurements were taken. In addition, scanning electron microscopy (SEM) and energy dispersive scanning X-ray (EDX) was used in microstructural investigations. It was observed that Cu-13.5Al-4Ni shape memory alloy samples, which were aged for different times under constant pressure and aged under different pressures for equal times, as well as transformation temperatures, and other thermodynamic parameters, the structured parameters such as microhardness, grain size, and crystallite size.