Architecture of functionally graded ceramic/metallic coatings by electron beam-physical vapor deposition

Electron beam physical-vapor deposition (EB-PVD) is considered to be a cost-effective and robust coating technology that has overcome some of the difficulties or problems associated with the metal spray, chemical vapor deposition, and other physical vapor deposition processes. EB-PVD offers many desirable characteristics such as relatively high deposition rates (up to 100-150 μm/minute with an evaporation rate approximately 10-15 Kg/hour), dense coatings, precise composition control, columnar and polycrystalline microstructure, low contamination, and high thermal efficiency. Various metallic and ceramic coatings (oxides, carbides, nitrides) have been deposited at relatively low temperatures. EB-PVD has the capability of producing multicomponents and multilayered metallic/ceramic coatings on large components by changing the EB-PVD processing conditions such as ingot composition, part manipulation, and electron beam energy. Attachment of an ion beam source to the EB-PVD process offers additional benefits such as dense coatings with improved adhesion. This paper reviews the evolution of high temperature protective coatings along with the architecture of functionally gradient coatings (FGC) for advanced turbine systems. The microstructure of the FGC was changed from equiaxed to columnar grains without creating the presence of discrete interface by manipulating the EB-PVD coating process parameters. Promising results of thermal barrier coatings are presented after 65 thermal cycles of exposure at 1135 °C (2075 °F) for 24 hours in air.