Carbon distribution in multi-phase γ-TiAl based alloys and its influence on mechanical properties and phase formation

Abstract Advanced intermetallic γ-TiAl based alloys are attractive light-weight materials for high-temperature application. In order to extend their service temperature limits, alloying with low-density elements, such as C, is of particular interest and has been shown to effectively increase high-temperature strength as well as creep resistance. In the present study the local chemical composition of the constituent phases of the so-called TNM alloy and a C-containing derivative thereof is characterized by atom probe tomography. In both alloys Mo is found to preferentially locate in the βo phase, in contrast to Nb, which is dispersed in similar levels in all phases. In the C-containing alloy, C is enriched in the α2 phase, dissolved in the γ phase, but depleted in the βo phase. Furthermore, the investigation of interfaces through site-specific sample preparation reveals segregation of C at phase interfaces and their close vicinity. Finally, a correlation of the mechanical properties with the C distribution is established by nanoindentation technique. Both the γ and the α2 phase significantly harden through the addition of C, which is in good agreement with the C concentration present within these phases as observed by atom probe tomography. However, the βo phase softens through the addition of C, which is not a direct consequence of the C distribution, but follows from the absence of finely dispersed ωo particles in the βo phase of the C-containing alloy.