Titanium Nitride and Yttrium Titanate Nanocomposites, Endowed with Renewable Self-Healing Ability

The environmental barrier coating (EBC) has been studied to protect the silicon carbide blades of the next-generation gas turbine engine of aircraft from superheated water vapor. The upper ceramic layer of EBC is brittle, therefore, cracks can occur under the impact of foreign debris and spread toward the lower layers, which leads to the destruction of this structure. Therefore, self-healing structural ceramics is a promising solution to this problem, but they still have some critical drawbacks. First, a healing agent such as SiC is highly volatile in water vapor. Second, the uniform distribution of the healing agent in the matrix can cause internal stress, which can break the composite. Finally, in most cases, the self-healing function can only be used once. Here, functionally graded Y2Ti2O7-Y2TiO5-TiN composites are produced by hot pressing and nitriding and then their self-healing function is demonstrated. The oxidation of TiN to TiO2, associated with volumetric expansion, can heal surface cracks. In addition, the bending strength of the composite can be restored. The self-healing ability is renewable at least until the second heating cycle. These optimistic results can pave the way for the development of a new class of materials with permanent self-healing ability.