The present study shows that a FL microstructure with a colony size of ≈1 mm can be refined to a fine FL structure with a grain size of 10–30 μm. More importantly, the present refinement was achieved merely by heat treatment, and no mechanical processing such as hot extrusion and canned forging was involved.
Three different heat treatment routes were designed, each involving a specific cooling rate and thus a particular refining mechanism, but leading to a similar result. The refining mechanism is massive transformation and the precipitation of α laths of four different orientations in individual γ grains in the NQC case, the formation of feathery γ and its spheroidization in the OC case, and discontinuous coarsening in the AC case. Because of the involvement of different cooling rates, the three different routes may be applied for microstructure refinement of TiAl alloys of different sizes.