Effect of Cr on microstructure and oxidation behavior of TiAl-based alloy with high Nb

Abstract

Three novel multi-microalloying TiAl-based alloys containing high Nb were designed and fabricated. Thermogravimetric method was applied to investigate the influence of Cr on the oxidation behavior of high Nb-TiAl alloy at 1,073 K for 200 h in laboratory air. The 2at.% and 4at.% Cr were added into the alloy, (respectively named 2Cr and 4Cr compared to the Cr-free ternary alloy, 0Cr alloy). The alloys’ microstructure and composition as well as the composition distribution of the oxidation scale were analyzed by means of Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and X-Ray Diffractometry (XRD). The results show that the addition of Cr decreases the grain size of the Nb-TiAl alloy and leads to a transformation from a fully lamellar structure to a nearly fully lamellar structure. When oxidized at 1,073 K for 200 h, the oxidized mass gain of the alloy increases with an increase in Cr addition amount in the first 100 h and decreases in the last 100 h. With the increase of Cr content, the oxidation surface turns compact but uneven in morphology, which may affect the oxidation resistance of the alloy by increasing the peeling off risk of the oxidation layer at friction conditions.

Keywords

• TiAl-based alloys
• microstructure
• oxidation
• Cr addition