Composite Nature of Coatings

The surface of a material may be exposed to wear, corrosion, radiation, electrical or magnetic fields and other phenomena and must have the ability to withstand these environments. In addition, the surface may be required to provide certain desirable properties such as reflectivity or high thermal conductivity. This can be accomplished by coating the base material to obtain a composite in which the surface properties may be considerably different from those of the substrate. 1 1 

Mechanical Wear and friction Toughness and ductility Strength and hardness Adhesion 

Chemical Difrusion Oxidation and corrosion Electrochemical reactivity 

The surface of a material exposed to the environment experiences wear, corrosion, radiation, electrical, or magnetic fields and other phenomena. It must have the properties needed to withstand the environment or to provide certain desirable properties, such as reflectivity, semiconductivity, high thermal conductivity, or erosion resistance. Depositing a coating on a substrate produces a composite material and, as such, allows it to have surface property, which can be entirely different from those of the bulk material. 

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