Electron microscopy of new martensites with long period stacking order structures in Ni50AlxMn50-x alloys I. Structures and morphologies

The martensitic transformations in Ni50AlxMn50-x (16.0 ≤ x ≤ 20.5) alloys were extensively studied by electron microscopy observations at ambient temperature and differential scanning calorimetry measurements. As a result, a new martensite with 10M (15R, (32)3) long period stacking order structure was found for x ≥ 19.0. For x ≤ 17.0, the martensite was invariably 14M (7R, (52)). For 17.0 ≤ x ≤ 19.0, various martensites were found, and the situation was in between the above two cases. Based on these results, a phase diagram to explain various martensitic transformations was proposed.