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Abstract

To improve the ductility and fracture strength of TiAl alloys, one of the crucial tasks is the correct understanding of the deformation mechanisms on different scales. Particularly, in a two-phase (γ and α₂) lamellar structure which consists of various interfaces and lamellae on the nano- to micrometre-scale, the importance of having such a multiscale modeling is obvious. Indeed, for a better interpretation and understanding of experimental observations based on the knowledge of nano-scale deformation mechanisms, such as lamellar boundary sliding and/or dislocation nucleation as well as dislocation dissociation, an atomistic modeling is required. Quantitative values for stacking fault energies and other key quantities for various interfaces in the lamellar microstructure can be obtained through ab-initio density functional theory (DFT) calculations. Basic processes and deformation mechanisms in a lamellar microstructure can be modeled via molecular dynamics (MD) simulations, ideally benchmarked to DFT results. In this project, we have carried out atomistic studies by applying DFT and MD approaches on a two phase γ/α₂ lamellar microstructure. On the DFT level special emphasis has been put on both tensile and shear properties of different lamellar boundaries. The results show that, surprisingly the normal strengths of all different interfaces as well as bulk phases are in the same range, while they have different interfacial energies and work of separations. Furthermore, the 60°-rotated and 120°-rotatedγ/γ interfaces display an easy shearing configuration. From MD simulations using an embedded-atom method type potential we found out that shear loading of a true twin type γ/γ interface in the [11-2] direction results in grain boundary migration, while for loading in the [1-10] direction no migration but grain boundary sliding and stacking faults creation occurs. These initial simulations already show that the interplay between geometry and loading conditions has an impact on the deformation mechanism.