Abstract:For precise plastic deformation, microstructure control is essential especially for β-solidifying γ-TiAl alloy with duplex structure. Based on stereology, the microstructure of isothermally compressed γ-TiAl alloy was divided into β₀ grains, remnant α₂/γ lamellar colonies, α₂ and γ grains. The results show that the volume fraction of β₀ grains slightly increases in the isothermally compressed γ-TiAl alloy with the increase of height reduction. Meanwhile, the volume fractions of remnant α₂/γ lamellar colonies and α₂ grains decrease. However, the volume fraction of γ grains increases from 64.39% to 78.47%. According to the quantitative results, the α→γ phase transformation was investigated in-depth, and it is found that isothermal compression accelerates the α→γ phase transformation. The first α→γ phase transformation is similar to ledge-controlled transformation, through which remnant α₂/γ lamellar colonies finally convert into γ grains in isothermal compression. The second is achieved by α/γ phase interface immigration.

Key words: TiAl alloy; stereology; digital image analysis; microstructure; phase transformation