In-situ observation of martensitic transformation in Cu-Al-Mn cryogenic shape memory alloy

A low temperature metallographic in-situ observation apparatus was designed to research the martensitic phase transformation of Cu-Al-Mn cryogenic shape memory alloy. Some martensitic transformation rules were summarized. In the processing of martensite phase transition, martensite grains gradually grow up as the temperature decreases and shrink as warming up. Many martensites phase with different orientation formed in a grain (self-accommodation of martensite variants). The result also suggested an interaction between martensites. Appearance of a new martensite will make another martensite disappear. When continue cooling the sample, the martensite which is disappeared will reappear. The nucleation site of martensite can be everywhere. However, nucleation rate in the grain boundaries and sample boundaries is higher than that of other sites. Martensites can grow cross the grain boundaries into another grain. The crossing point can be a new nucleation point.