Development of directionally solidified γ-TiAl structures

To further develop the technology associated with directional solidification of gamma titanium aluminides a research program was initiated between Carleton University and the Structures, Materials and Propulsion Laboratory, Institute for Aerospace Research, National Research Council Canada. Relatively fine, continuous, and aligned columnar microstructures with varying lamellar orientations within the individual grains are produced using two gamma titanium aluminide compositions under varying processing conditions. Numerical simulation of the directional solidification casting process is employed to better understand the formation of the as-cast microstructure and to suggest processing improvements. The orientation of the columnar grains is shown to be a function of the shape of the solidification interface while the final lamellar orientation seems to depend on the temperature gradient during processing.