Microstructure, Mechanical Properties, and Shape Memory Effect of Annealed Cu-Al-Ni-xCo Shape Memory Alloys

In order to develop the main applications of Cu-based shape memory alloys (SMAs), the effect of annealing time and temperature on the microstructure, mechanical properties, and shape memory characteristics of Cu-Al-Ni-xCo SMAs (x is 0.38, 0.6, and 1.2 wt.%) were studied. A distinct consideration is lent to the microstructural changes, phase transformation, and mechanical properties, which might take place in accordance with the changes in the alloying element/composition and/or heat treatment implementation. Because of this, the microstructural changes were portrayed using a variable-pressure scanning electron microscope, energy-dispersive spectrometer, and x-ray diffraction. The strength and hardness were determined using a universal Instron testing machine and Vickers hardness testing machine, respectively. The shape memory test was carried out using specially designed with an insulated system. The results indicated that the phase transformation of Cu-Al-Ni-xCo SMAs can be changed by varying the annealing temperature and time, and subsequent annealing can cause an effective impact on the shape memory effect. Moreover, it was also realized that the annealing treatment is involved in controlling the presence of γ ₂ phase precipitate, thereby, improving the mechanical properties. The highest fracture stress and strain of 860.94 MPa and 9.43%, respectively, were determined in the Cu-Al-Ni-0.6 wt.% Co SMAs after being annealed at 500 °C for 3 h. In particular, the Cu-Al-Ni-1.2 wt.% Co SMAs obtained 84.08% recovery, which is the highest strain recovery after being annealed at 500 °C for 3 h.