Origin of enhanced room temperature ductility in TiAl alloys: Reducing activation difference of deformation mechanism of γ phase

Abstract

TiAl alloys have been studied widely as promising candidates for high-temperature applications, while the application has been hindered due to the lack of room temperature ductility. Herein, 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 the composition of γ phase in both TiAl alloy composed of γ and α2 phases, 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 carefully calculate the change in activation factors of deformation mechanism according to each additional element (Cr and Nb) in TiAl alloy. As a result, it can be understood that the deformation mechanism of the γ phase in TiAl alloys 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 of TiAl alloy decreases as Nb is added, which leads to the activation of all deformation mechanisms in the γ phase during deformation, 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 γ phase of TiAl alloys, which will open a new era to develop TiAl alloys with enhanced ductility for various structural parts in automotive and aerospace industries.