Reinforcing and toughening mechanism of the in-situ metastable nanostructured alumina-titanium oxide composite coating

High porosity and high brittleness are the main reasons that limit the long-term service life of the alumina-titanium oxide composite coating. Herein, a metastable nanostructured alumina-titanium oxide composite coating with high density and high properties was synthesized by plasma spraying of TiO2-Al composite powder. The main phases of the metastable nanostructured alumina-titanium oxide were γ-Al2O3, TiO and AlTiO2. The coating, as prepared, contains various metastable microstructures, such as fine-grained, intra-/inter-granular, and "self-locking" microstructures. These metastable microstructures are important for the improvement of hardness and toughness of the coating. Compared with other alumina-based composite coatings, the metastable nanostructured alumina-titanium oxide composite coating showed the most impressive overall performance. The reinforcing and toughening mechanism of the metastable alumina-titanium oxide composite coating included fine grain strengthening and self-toughening of the metastable microstructure.