Atomic scale self accommodation observed at hcp/dhcp martensitic transformation interfaces

The martensitic hcp→dhcp transformation was studied in single crystals of Co-0.85at%Fe by transmission electron microscopy (TEM) methods. During in-situ heating dhcp lamellae emerge into the hcp areas of the TEM specimens. The minimum thickness of the lamellae is about 15 close packed planes. Frequently lamellae are observed that grow in thickness by the movement of superledges that are up to about 100 close packed planes in height. The partials at the fronts of the transformation were analysed on an atomic level in TEM images with atomic resolution. The analysis shows that the transformation fronts consists of a sequence of very narrow dipoles compensating their long range strain fields. Since dipoles of a common Burgers vector are observed it is proposed that their short range interactions might promote their correlated nucleation.