Orientation relationship and interfacial structure between ζ-Ti5Si3 precipitates and γ-TiAl intermetallics Original Research Article

The orientation relationship (OR) and the interface structure between Ti5Si3 precipitates and the γ-TiAl phase have been investigated systematically. The habit plane of Ti5Si3 in TiAl was determined to be (0001)ζ‖(111)γ. However, there is no low-index direction of the two phases parallel to each other in the plane. This “abnormal” OR has been predicted precisely from a recently developed geometrical method, in which the overlap of reciprocal lattice points of two adjoining crystals is utilized to obtain the optimum OR. In spite of the significant difference in crystal structure between TiAl and Ti5Si3, the interface was found to be semi-coherent with good matching and has the largest possible displacement shift complete lattice corresponding to the bicrystal. The energy of the interface is also discussed. The translational state between the two lattices and the chemistry of the terminating plane of Ti5Si3 have been determined by using high-resolution transmission electron microscopy.