Development of directionally solidified γ-TiAl structures

Gamma titanium aluminide intermetallics offer the potential for significant weight savings when substituted for nickel-base superalloys in some gas turbine applications such as low pressure or power turbine blades. Unfortunately, the widespread use of these alloys has been delayed by two risk factors: a poor balance of mechanical properties and uncertainties regarding the feasibility of economic component production. The directional solidification casting process applied to gamma titanium aluminides may be a promising manufacturing method capable of overcoming these issues. ther 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.