Homogenization kinetics of a cast Ti48A12W0.5Si alloy

The homogenization kinetics of a cast Ti48A12W0.5Si alloy with a duplex microstructure was studied in terms of γ-phase dissolution and α-grain growth. It was found that the measured volume fraction of remnant γ grains can be well simulated by a model of interface-controlled dissolution in a dislocation mechanism, instead of a diffusion-controlled one. The activation energy for the α/γ interface reaction was found to be Qint = 476 kJ mol−1, which is much higher than the interdiffusion activation energy in TiAl alloy. The grain growth of α phase during homogenization can be categorized into three stages. During the first stage, where the volume fraction of remnant γ grains is higher than about 10%, the growth of α grains follows the parabolic law D = k1t0.2, and the activation energy for grain growth was calculated to be Q1 = 442 kJ mol−1, very close to the Qint for α/γ interface reaction. In the second stage, where few fine γ grains (1–10 vol.%) remained, a dramatic grain growth occurs. During the final stage, as the single α phase is obtained, the coarsening of α grains again satisfies the grain growth law D = k3t0.4, with the grain growth activation energy Q3 of 147 kJ mol−1, lower than the reported interdiffusion energy of γ phase.