Orientation relationship and interfacial structure between zeta-Ti5Si3 precipitates and gamma-TiAl intermetallics

The orientation relationship (OR) and the interface structure between Ti5Si 3 precipitates and the mu TiAl phase have been investigated systematically. The habit plane of Ti,Si, in TiAl was determined to be (0001)(zeta)paralle l to(111)(gamma) 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 overl ap of reciprocal lattice points of two adjoining crystals is utilized to ob tain the optimum OR. In spite of the significant difference in crystal stru cture between TiAl and Ti,Si,, 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 als o discussed. The translational state between thr two lattices and the chemi stry of the terminating plane of Ti,Si, have been determined by using high- resolution transmission electron microscopy. (C) 2000 Acta Metallurgica Inc . Published by Elsevier Science Ltd. AII rights reserved.