Different twinning arrangements in Ni5Al3 plates grown inside the B2 phase in Ni62.5Al37.5 samples are descrubed on the basis of conventional and high resolution electron microscopy images and electron diffraction. The plate morphology is comparable with that of pure 2M martensite plates. The choice of ordered variants within a plate is dictated by the ordering coherency of the twin plane. No dislocations were observed at the primary plate-matrix interfaces. An explanation using the streaking due to aperiodic twinning is given for unexpected reflections.
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