Phase Transformations in γ-Aluminide, Ti–46.5Al–xNb–yCr–zMo–0.3B (x = 3.5, 5; y, z = 0, 1, 2; y + z = 2) Alloys

The response of as-cast microstructure of six γ TiAl alloys with 46.5 at.% Al and varying Nb, Cr and Mo additions in the temperature range of 1150–1400 °C in water quenched and furnace cooled condition has been studied. The microstructural constituents, their morphologies and phase fractions along with their hardness were determined. The microstructural features at various temperatures were correlated with the transformation temperatures obtained through DSC. The alloy system investigated lies in a two phase α + β field from about 1430 °C down to about 1288–1272 °C. A three phase region below the two phase field exists, with the eutectoid temperature lying in the range of 1155–1076 °C. The volume fraction of β/B2 phase in water quenched condition is generally higher than in furnace cooled condition as sufficient time is allowed for its decomposition in later condition and reaches its equilibrium which in turn decreases the hardness of alloys in furnace cooled condition.