Conservative motion of parent-martensite interfaces

Parent-martensite interfaces are modelled in this work as semi-coherent interfaces comprising coherent terraces reticulated by arrays of defects that accommodate coherency strains. It is demonstrated that such interfaces can migrate conservatively if one set of defects is an array of disconnections (transformation dislocations) that can glide along the terraces. The topological character of disconnections (Burgers vector and step height) that can glide in this way is elucidated. Experimental observations of martensitic interfaces in ZrO2, Ti-10 wt.% Mo and ferrous alloys are then examined in the light of this understanding. In the cases reviewed, it is found that the interface structures observed are consistent with the terrace/disconnection model proposed.