Coatings are appropriate when the service requirements of a component are such that a high performance material is required. Materials that survive impact, abrasion, corrosion, and have good galling resistance under high loads are typically expensive and are difficult or impossible to machine. It makes economic sense to apply a high performance material onto a component where these properties are needed, and use a substrate material that is significantly less expensive to acquire and manufacture. Components like this are found in equipment such as oil field and industrial valves, pumps, combustion engines (both piston and turbine types), and the like; all have precision components that must survive extreme environments (Figures 9.1-9.3).