Effect of borate coating on oxidation resistance of γ-TiAl intermetallic compound

The pack boriding process has been used to treat γ-TiAl intermetallic compound at a boriding temperature of 940°C for a boriding time of 8 h. A dense and continuous borided layer ca. 15 μm thick was obtained on γ-TiAl. The X-ray diffraction pattern depicts a single borate phase 9(A1,Ti)2O3 B2O3 formed in the borided layer. Cyclic oxidation behavior of the borate coating has been investigated at an oxidation temperature of 800°C with a total exposure time up to 100 h in air. The mass gain of the borate coating was 1.6 mg cm−2, which is about three times lower than that of unborided γ-TiAl. The 9(Al,Ti)2O3 B2O3 phase decomposes slowly during the oxidation process at 800°C in air. The stable borate coating improves the high temperature oxidation resistance of γ-TiAl.