A coating, from a surface engineering point of view, is a layer of material deposited onto a substrate to enhance the surface properties for corrosion and wear protection. Factors affecting the choice of a coating include service environment, life expectancy, substrate material compatibility, component shape and size, and cost.
There is a wide range of coating processes for depositing many different types of material at thicknesses ranging from just a few microns, up to several millimeters. The different types of coatings can be categorized in many ways. One common approach is based on the manner in which the coating material is deposited on the substrate surface. This includes atomic deposition, particulate deposition and bulk coating or cladding.