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

The pack boriding process has been used to treat gamma-TiAl intermetallic c ompound at a boriding temperature of 940 degrees C for a boriding time of 8 h. A dense and continuous borided layer ca. 15 mu m thick was obtained on gamma-TiAl. The X-ray diffraction pattern depicts a single berate phase 9(A l,Ti)(2)O-3 B2O3 formed in the borided layer. Cyclic oxidation behavior of the berate coating has been investigated at an oxidation temperature of 800 degrees C with a total exposure time up to 100 h in air. The mass gain of the berate coating was 1.6 mg cm(-2), which is about three times lower than that of unborided gamma-TiAl. The 9(Al,Ti)(2)O-3 B2O3 phase decomposes slo wly during the oxidation process at 800 degrees C in air. The stable berate coating improves the high temperature oxidation resistance of gamma-TiAl. (C) 2000 Elsevier Science S.A. All rights reserved.