ANALYSIS OF HRTEM CONTRAST OF OVERLAPPING STRUCTURES AT TRANSFORMATION INTERFACES

Periodic contrast modulations were observed by high-resolution transmi ssion electron microscopy (HRTEM) methods at the trails formation inte rfaces between different close packed structures in CoFe alloys. Image simulations show that moire fringe patients caused by overlapping clo se packed lattices agree with the experimental observations. The moire patterns occur at interfaces that are inclined in the TEM projection. At the phase boundaries periodic arrangements of different transforma tion dislocations can lead to self-compensation cf the long range stra in fields. Since the periodicity of the dislocation arrangement can be equal to the periodicity of the moire fringe pattern a simple interpr etation of the contrast modulations in terms of localised periodic str ains is not possible. This makes it necessary to analyse the transform ation dislocations by Burgers circuits carried out in cross-sectional HRTEM images.