Titanium aluminides containing 20–30 atom percent Al can suffer from severe subsurface embrittlement (alpha-case) when exposed to air at elevated temperatures for extended periods. For example.the alloys Ti-24Al-12.5Nb-1.5Mo and Ti-24Al-8Nb-2Mo-2Ta (based on the Ti3Al alpha-2 intermetallic compound) embrittle to a depth of about 80 microns during 1000 hours exposure to air at 815°C (1500°F), resulting in major reductions in tensile properties. Plasma-sprayed coatings of the MCrAlY and MCr types deposited over a thin diffusion barrier of chromium or tungsten, have been found effective in protecting these alloys against oxidation and embrittlement at this temperatures.
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McKee, D.W. Oxidation and Protection of Ti3Al-Based Intermetallic Alloys. MRS Online Proceedings Library 288, 953–958 (1992). https://doi.org/10.1557/PROC-288-953