A deposition process in which a source material in the form of an ingot (or rod) is vaporised through the bombardment of an electron beam from a tungsten filament charged under high vacuum and re-solidifies as a coating on a target surface. Deposition rates can range from a few nm per minute to several µm per minute enabling control of the coating structure and morphology. PVD methods are typically either ‘line-of-sight’ or ‘semi-line-of-sight’ and utilise electron beam guns with power levels of a few 10s to 100s of kW. Rotation and translational of the target substrate assists the uniform coating of the outer surface of complex geometries.
EB-PVD is the preferred process for the generation of thermal barrier coatings (TBC) in jet engines. As the name suggests the TBC provides a layer of thermal insulation on the turbine blade enabling the blade to run cooler for an identical turbine entry temperature or reducing the need for blade cooling whilst maintaining its creep life.
The term CVD covers a group of processes that deposit a solid material from a gas phase onto a target substrate. At ambient temperature or just above and usually diluted in a carrier gas, the precursor gases are introduced into the reaction chamber where they come into contact with a heated substrate and either decompose or react. The substrate temperature will influence the outcome of the reaction or decomposition processes that take place at the substrate surface. CVD is a versatile technique that can be used to coat both ceramic and metallic layers or produce bulk materials.
CVI is a derivative of CVD enabling the infiltration where material is deposited within the bulk of a porous structure. For example, the infiltration of fibre performs to produce ceramic matrix composites such as C-C, C-SiC and SiC-SiC with enhanced oxidation resistance.