Microstructural evolution in an Ni-Mn-Ga alloy during compression

Microstructural aspects and interfacial characteristics of deformed martensite variants in a compressed Ni55Mn20Ga25 (at.-%) alloy have been investigated using transmission electron microscopy. It is shown that the undeformed specimen exhibits a well accommodated morphology and a straight and well defined interfacial boundary. After deformation, reorientation of martensite variants occurs at the expense of unfavourable martensite variants, and the interfacial boundary changes from sharp and straight to curved and irregular. Meanwhile, lattice defects are formed inside the variants even in slightly compressed samples. With increasing deformation, high density lattice defects are generated and rearranged inside the variants as well as in the interfacial boundaries between variants.