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 degrees 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.