Microstructural changes of a CuZnAlMnNi shape memory alloy due to cooling in liquid nitrogen

The microstructures of a CuZnAlMnNi alloy immediately after quenching, as well as further cooling in liquid nitrogen, were investigated by scanning electron microscopy and transmission electron microscopy. It was found that when the as-quenched alloy was subjected to cooling in liquid nitrogen, the spear-like martensite changed into the granular microstructures, resulting in the destruction of the continuity of the martensite plates and the increment of the boundary area. Simultaneously, the stacking faults in the original martensite plates became confused and the degree of ordering decreased from 0.0929 to 0.0417 إ.