Micro and macromechanical investigations of CuAlNi single crystal and CuAlMnZn polycrystalline shape memory alloys

The micro and macromechanical transformation behavior of single and polycrystalline shape memory alloys was investigated using in situ optical microscopy. An interference filter was used on the microscope to enhance observation of grain boundaries and martensitic plate formation and growth. Experiments on CuAlMnZn polycrystals as well as CuAlNi single crystal shape memory alloys were performed and results are reported in this paper. Cyclic behavior, temperature effects and strain rate effects were studied in detail. Excellent correlation between stress relaxation and temperature decay at several strain rates was achieved. At high strain rates, a dramatic redistribution of martensitic variants was seen in the single crystal specimens after loading to a fixed strain. Tests were performed at different temperatures to help identify the mechanism for variant redistribution.