A technique for determination of γ/γ interface relationships in a (α2 + γ) TiAl base alloy using TEM Kikuchi patterns

A new method for unambiguous differentiation and orientation determination of six γ variants and α2 phase in a two phase TiAl base alloy is presented. The approach involves automatic collection of transmission electron microscopy (TEM) Kikuchi patterns by a digital CCD camera at regular distance of nano steps through nanoprobe scanning. The Kikuchi patterns corresponding to various γ variants and α2 phase were distinguished through superlattice bands. The procedure is compared with other methods for identification of six γ variants and α2 phase in terms of their spatial and angular resolutions as well as easiness and rapidity for large data collection. As an example, the technique is utilised to characterise the lamellar structures of a Ti–48(at.%)Al–2Cr–2Nb alloy resulting from heat treatment at high temperature α domain followed by furnace cooling. Each lamella is labelled with its respective γ variant or α2 phase. The frequencies of the γ and γ/γ interfaces were determined. Moreover, it is noticed that some of the 0° and 180° γ/γ interfaces are in fact semi-coherent, and present a slight deviation from their ideal misorientation.