Origin of Enhanced Room Temperature Ductility in Tial Alloys: Reducing Activation Difference of Deformation Mechanism of γ Phase

We systematically investigated the effect of tensile loading direction and additional elements (Cr and Nb) on the initial deformation mechanism in the γ phase of TiAl alloys, which is one of the crucial factors to decide room temperature ductility. First, we carefully chose two different TiAl alloys with limited and enhanced ductility. Second, by synthesizing the sample with a single γ phase via extracting γ composition in both TiAl alloys, the initial deformation mechanism of γ phase is confirmed depending on alloy composition as well as loading direction using an in situ transmission electron microscopy. Third, using the first principle density functional theory calculation, we calculate the change in activation factors of deformation mechanism according to each additional element (Cr and Nb) in TiAl alloys. As a result, it can be understood that the deformation mechanism of the γ phase changes depending on the additional element as well as loading direction. In particular, by comparing the experimental and theoretical study, it was revealed that the activation difference of three deformation mechanisms in the γ phase decreases as Nb is added, which leads to the activation of all deformation mechanisms in the γ phase, and hence obtains the enhanced room temperature ductility in TiAl alloys. Our results provide an effective strategy for enhancing room temperature ductility of TiAl alloys via reduction of activation difference of deformation mechanisms in the γ phase of TiAl alloys, which will open a new era to use TiAl alloys as various structural parts with enhanced ductility.