Multilayer Coating for Protection of Titanium Aluminides from Oxidation and Hydrogen Embrittlement

Application of gamma titanium aluminides in gas turbine engines is limited by the room-temperature ductility loss that occurs when exposed to moist air or hydrogen-bearing gases. These gasses are typically found in a gas turbine engine environment. A protective and less expensive multilayer coating will protect titanium aluminides from oxidation and hydrogen embrittlement. The proposed coating will consist of a Two-Phase-Glass (TPG) overlayer over a dense A1203 base layer. The Al10 layer will prevent hydrogen diffusion into the alloy. The TPG overlayers will shield the underlying Al203 layer and base intermetallic alloy from direct exposure to the environment. Coated and uncoated tensile test samples will be prepared and exposed to moist air at temperatures ranging from 200 deg C and room temperature ductility will be evaluated. In addition, coated and uncoated coupon specimens will be exposed to isothermal and cyclic oxidation. One or two the best coatings from Phase I effort will be selected for further testing in Phase II. Phase II studies will include tests in pure hydrogen atmosphere, fatigue tests on actual engine parts in the turbine environment. Tests in pure hydrogen are also proposed as a Phase I option.