New‐Type Oxidation Barrier Coatings for Titanium Alloys

Herein, a new type of oxidation protection coating for Ti alloys is developed based on a perhydridopolysilazane preceramic polymer and particulate AlB₂, Si, B, and Ti₃AlC₂ (so‐called MAX phase) fillers; MAX phases are used due to their high temperature and corrosion resistance, thermal shock resistance, and self‐healing capability. For coating consolidation, the as‐coated samples are pyrolyzed in argon or nitrogen and exposed to air at 800 °C for up to 100 h. Although coatings containing AlB₂ or elemental Si and B show a small mass gain in the initial state of exposure to air and after no mass gain up to 100 h, MAX phase‐loaded samples show a significant mass gain up to 7 h of exposure and a sudden mass decrease, which corresponds to coating layer spallation. The mechanisms leading to oxidation protection in AlB₂‐filled systems are explained with an alumina layer formation and a glass formation from the preceramic polymer. In Si‐ and B‐filled systems, a borosilicate glass phase may be able to reduce the oxygen diffusion capability and the MAX phases as fillers need further investigations; they may cause thermally induced mechanical stresses in the protective coatings.