Effects of tailoring microstructure on short-term creep behavior of high Nb containing TiAl alloys under various stress levels

In this work, the short-term creep behaviors of high Nb containing TiAl alloys with different microstructure characteristics at 800 °C under a wide range of stresses of 150–350 MPa were investigated in detail. In order to tailor microstructure of high Nb containing TiAl alloys, composition design strategies were applied, including the change of Al content and the introduction of non-metallic element C and rare-earth oxide Y₂O₃. Microstructure analysis shows that increasing Al content from 43 at.% to 46 at.% will not only change the phase constitution by changing the solidification behavior, but also affect the existence form of element C, that is, in the form of dissolved carbon atoms in low-Al alloy and Ti₂AlC precipitate in high-Al alloy. Creep results confirm that both increasing Al content and introducing C and Y₂O₃ can effectively reduce the steady-state creep rate and enhance the creep resistance, but the latter has a more significant effect. In addition, the creep behavior of high Nb containing TiAl alloys strongly depends on the stress level, and corresponding creep deformation mechanism changes from grain boundary/lamellar interface sliding under low stress to dislocation motion under high stress. Meanwhile, the correlation between the critical stress value on creep mechanism transition and the alloy composition/microstructure was clarified.