High-resolution image simulation of overlap structures in TiAl alloy

High-resolution electron microscopy (HREM) images of the overlap structures in TiAl have been studied by the comparisons of experimental techniques and theoretic simulations. Several misunderstandings about TiAl microstructures were corrected. First, studies revealed that the reported 9R structures in TiAl must result from the overlap of two twin-related γ laths. They were not the true 9R structure. Second, the fringes (FR) between the γ and α2 phases have once been misconsidered as the stacking faults fringes which promoted the α2 ↔ γ phase transformations. This work proved them to be the fringes caused by the overlap of the α2 and γ phases. Through study of the imaging of the overlap structures, a new formation mechanism of the fringes has been proposed.