Smart Coating Technology: A Glaze-Based Surface with Self-Healing Capabilities

Tribological interfaces within aircraft engines represent an exceptionally demanding domain due to their operation in high-temperature environments, a factor linked to the engines' efficiency and, consequently, a source of significant economic concern. It is well known that metallic oxides play an important role in tribological systems, particularly at such high temperatures. Some materials are especially effective in forming an oxidation layer (i.e., glaze layer) which decreases the friction and wear of the surface at high temperatures. Cobalt-based alloys (e.g., Haynes 25) are strategically employed throughout gas turbine engines due to their capability of forming these glazes. Owing to the similarity of these glazes to a coating, some efforts have been made to create thermally sprayed coatings that mimic their chemistry, showing promising results. For the current study, coatings based on cobalt and chromium oxides were tailored using suspension plasma spray over Inconel 718 substrates. However, during the wear tests performed at elevated temperatures a segregation of phases was observed, leading to the development of a cobalt-rich layer at the top surface. This segregated phase was also observed in the inside of the coating, closing cracks and defects. The results explore the tribological performance of these coatings (i.e., friction and wear), as well as their ability to recover from artificial damage introduced on the surface, with a characterization of the segregated phase.

Keywords: Glaze-based coatings, Self-healing, Tribology, Metallic Oxides, Suspension Plasma Spray.