Kinetics of Grain Growth in a γ-Based TiAl Alloy

The strength and ductility of two-phase TiAl alloys are very dependent on microstructural size and morphologies and much research is being devoted to obtaining optimal properties 1, 2, 3. The large grain sizes and solute segregations associated with conventional castings have forced much of the work to be focused on obtaining finer microstructures, both in terms of grain sizes as well as lamellar spacings. The latter are refined by exposing the alloys to high temperatures and cooling at different rates and it is difficult to obtain different lamellar spacings without varying the grain size. An alternative way of varying structure is to obtain equiaxed microstructures in which the size of the γ grains is refined to the level of the lamellar spacings [4]. To achieve such fine grain sizes some elements (such as C or B) are added to act as grain refiners during thermomechanical processing or powder consolidation when the alloys are produced by atomisation. Little work has been carried out, however, to understand the stability of the structure and in particular the kinetics of grain growth leading to coarse microstructures