The Principles and Applications of Chemical Vapour Deposition

SUMMARYChemical vapour deposition (CVD) is a technique that relies on the formation of a gaseous species containing the coating element within a coating retort or chamber. Alternatively, the gaseous species may be generated external to the coating retort and introduced via a delivery system. These gaseous species (eg, chromous chloride) are then allowed to come into contact with the surfaces that require coating. The retort is held at a high temperature, normally in excess of 800°C. The application of this thermal energy and the presence of a reducing atmosphere results in the decomposition of the molecules containing the coating element which are subsequently deposited onto the surface of the substrate.Using the CVD method a wide variety of coatings may be formed, ranging from soft, ductile coatings to those with hard, ceramic like properties. Coating thicknesses can vary from a few micron to over 200 mm, with hardnesses in the range 150–3000 HV (0.1Kg). Coatings formed by the CVD method are currently being used to combat the severe attrition of components used in a variety of industrial situations where corrosion, oxidation or wear is experienced.The methods commonly used to apply CVD coatings will be discussed and their advantages and limitations examined. Several case studies will be highlighted, where CVD coatings have been used to solve specific industrial problems.