Giovanni Di Girolamo

Thermally sprayed nanostructured coatings for anti-wear and TBC applications: State-of-the-art and future perspectives

In the last decade the interest in nanostructured coatings has grown because of their potentially outstanding functional properties compared with their conventional counterparts. Thermal spraying is a cost-effective industrial technology suitable for deposition of thick composite and ceramic coatings. The control of processing parameters is an interesting challenge when agglomerated nanostructured powders are employed. These particles should be only partially melted to preserve their starting nanostructure, thus generating a coating with a unique microstructure, typically composed of semi-molten areas embedded in the surrounding fully melted binder. This chapter reviews state-of-the-art and future perspectives of thermally sprayed nanostructured coatings. Typical detrimental effects associated with high temperature and the spraying environment – carbide dissolution and decarburization – should be minimized during processing of cermet particles. The HVOF process allows fabrication of dense coatings with enhanced wear resistance. Nanostructured composite coatings exhibit enhanced toughness and resistance to crack propagation, resulting in improved wear resistance, as observed for Al2O3-TiO2 coatings for marine applications. In turn, nanostructured zirconia-based coatings, produced by atmospheric or suspension plasma spraying, are promising thermal barriers for turbine engines because of their toughness and thermal cycling resistance.

Current Challenges and Future Perspectives in the Field of Thermal Barrier Coatings

This chapter describes how ceramic thermal barrier coatings (TBCs) are usually applied on metal components of aircraft engines and land-based gas turbines, with the purpose to extend their lifetime as well as to increase performance and durability, by increasing the operating temperature. The TBCs have to satisfy basic requirements in terms of low thermal conductivity, high stress compliance, high sintering resistance as well as high resistance to the environmental attack promoted by oxygen, molten salts and CMAS (calcium-magnesium-alumino-silicate) deposits. This chapter is aimed at analyzing the state-of-the-art, the recent developments and the future perspectives in the field of TBCs, focusing the attention on advanced materials and new architectures as well as explaining the mechanisms affecting the failure of TBC systems.