Effects of different temperatures on the lamellar structure evolution in γ-TiAl alloys: A phase-field study

Abstract

The nucleation and growth processes during α2'→α2+γ transformation that leads to fully lamellar TiAl alloys were investigated by phase-field simulations. Since both α2 and γ are ordered solid solutions with a complex superlattice structure, it is still a great challenge describing the phase transition under different temperature conditions. In this article, sublattice model combined with gradient descent method was proposed for free energy calculation of the ordered phases. To verify the accuracy of this model, the formation of fully lamellar TiAl alloys was simulated. The simulation results demonstrated that the formation of lamellar structure is under the action of elastic energy and different variants show preferred orientation. It was also indicated that the distribution of lamellar structure at different temperatures is different. For example, at 1100 K, the lamellae are dense and small, but they are coarse at 1300 K, 1200 K, 1000 K and 900 K, which is consistent with the experimental observations. These findings can verify the correctness of our free energy model and overcome the defect that the traditional polynomial free energy model can only simulate isothermal temperature conditions, thus greatly simplifies the computational complexity and gives us the opportunity to expand to other ordered phase systems.