A wide variety of surface treatments and coatings are applied to metals to enhance their performance, for example, to improve fatigue resistance, increase wear resistance, corrosion or oxidation resistance. Some of these treatments involve diffusion of one or more elements into the metal or alloy followed by post heat treatments. These processes included the familiar processes of carburizing, nitriding, and carbonitriding but also included less familiar processes such as ion nitriding and boriding. There are also a wide variety of coatings that are deposited by hot-dipping, electroless or electrolytic means, by physical or chemical vapor deposition, or by thermal or plasma spray. The technological significance of these processes is enormous.