Interphase precipitation in a γ-TiAl alloy

Interphase precipitation is a phenomenon observed in some steels, such as carbon–copper–nickel steels and vanadium alloyed carbon steels. It was observed that γ-based titanium aluminides, when exposed to elevated temperature, also showed interphase precipitation. An alloy of Ti 47Al–0.5 at.%W–40 wppm B was aged for l week in the temperature range 800–1200°C followed by furnace cooling. The transmission electron microscopy analysis of the alloy showed the growth of γ grains into the lamellar structure, which consisted of alternate plates of the γ and α2 phases. Interphase precipitation was found to occur at the γ/lamellar colony interface. These precipitates had an equiaxed faceted morphology with an aspect ratio of approximately 2:1. The precipitates belonged to either the α2 phase or the Ti 2Al(C, N) phase. The Shoji–Nishiyama orientation relationship has also been established between the advancing γ grain and both the α2 as well as Ti2Al(C, N) precipitates.