Plasma Spraying of Ceramic Coating with All Interfaces Bonded Chemically through a Ceramic Bond Coat Thermally Grown on Metal Substrate

Abstract

Plasma-sprayed ceramic coatings are widely used for corrosion protection of metallic parts in industries. However, conventional ceramic coatings bond to metal substrates mainly through mechanical interlocking, with a tensile adhesion lower than 40 MPa, which limits their high-load applications. In this study, a new strategy to enhance the adhesion of coatings to a level over 100 MPa is proposed through introducing a ceramic bond coat to create chemical bonding throughout all the interfaces within the coating system. The experimental approval is made using titanium (Ti) as a typical substrate and Al₂O₃-13TiO₂ (AT13) as a typical coating material. The ceramic bond coat on Ti substrate was introduced by thermal growing under different oxidation conditions. The AT13 coating was deposited at 300 °C which was determined following the critical bonding temperature theory. It is found that the chemical bonding for all interfaces between ceramic layers was achieved by dynamic wetting of spreading molten splats ensured by the critical bonding temperature concept. The tensile test was modified by reducing the effective contact area of AT13 ceramic coatings to the substrate, and the adhesion of the ceramic coating prepared by the new method ranged from 105 to 121 MPa. This study provides a new technological approach for the application of plasma-sprayed ceramic coatings in high-load environments.