Grain Refinement of a γ-TiAl Alloy Through Isothermal Forging and Heat Treatment

Effect of initial massive type structure of a gamma-TiAl based alloy on its hot deformed and stabilized microstructure was investigated. A gamma alloy with composition of Ti-47Al-12Nb-0.5Si was subjected to rapid quenching from a phase field. The quenched sample was deformed at high temperature. Further post deformation heat treatment was conducted to stabilize the as-deformed structure. It was shown that Nb and Si have important roles in grain refinement of the final product. Presence of niobium in the alloy made the diffusion controlled eutectoid reaction sluggish and assisted the formation of massive type gamma phase (gamma(m)) by rapid cooling from alpha phase field. Silicon addition assisted the microstructural refinement by forming hard and finely dispersed titanium silicide particles. These particles act as preferred sites for dynamic recrystallization during hot deformation. Massive gamma phase tends to deform uniformly and decompose to equilibrium phases after final heat treatment and results in a very fine grained microstructure.