TEM STUDIES OF MICROTWINS IN THE L10 PHASE IN 63.1 AT PERCENT NIAL

The high resolution electron microscopy and optical diffraction studie s on regions of L1(0) phase containing high density twins in 63.1 at.% NiAl have shown the presence of stacked structures of varying stackin g periodicities. These stacked structures, which may be considered as periodically microtwinned L1(0), are observed to be present in regions of L1(0) phase that exhibited profuse streaking, sharp satellites, or both, along (111BAR)L1(0) reflection. A stacking periodicity of 7, wh ich corresponds to the 7R structure, is, however, observed to be the m ost predominant.