The production of lamellar microstructures in intermetallic TiAl alloys and their characterisation

In the present work two types of lamellar microstructures in gamma-TiAl based alloys were investigated. In the one, a fully lamellar microstructure was produced by annealing in the single a-phase field and subsequent slow cooling. The resulting microstructure consisted of colonies of gamma-TiAl / alpha 2-Ti3Al which represent the original a-grains. Within each colony the gamma/alpha(2) are arranged in parallel and exhibit a specific crystallographic orientation. In the other, with the help of massive transformation and subsequent ageing, a new type of lamellar microstructure was produced which could not otherwise have been realised using conventional methods. In this case fine alpha(2)-Ti3Al lamellae orientated at an angle of 70.5 degrees to one another were precipitated out of the massively transformed gamma m. In addition to a detailed description of the microstructures and an analysis of the orientation relationships of the two types of microstructures during their formation, the nucleation of the 7 lamellae in the a, grains are investigated using transmission electron microscopy (TEM).