Superplasticity of Cu-Al-Mn-Ni Shape Memory Alloy

The microstructure and superplastic behavior at 450°C and 500°C in Cu-Al-Mn-based shape memory alloys were investigated using optical microscopy and a tensile test. It was found that a fine α (fcc) + β (bcc) two-phase structure with a grain size of 3 μm in diameter can be obtained in Cu-Al-Mn-Ni alloy by annealing at 600°C. The flow stress of Cu-Al-Mn-Ni alloy depends on the strain rate and the strain rate sensitivity is over 0.3 with an elongation of over several hundred percent, which shows that the Cu-Al-Mn-Ni shape memory alloy exhibits superplasticity. For the test temperature at 500°C and a strain rate of 5×10−4 s−1, a maximal elongation of 1150% was obtained. The formation of cavity stringers lying parallel to the tensile axis was observed and the size of the cavity was larger as the specimen was more highly deformed.