Many requirements concerned with wear and corrosion concentrate on the surface of compounds on componentss. As a concequence it makes sense to treat this part as all one part.

"You can consider the high demands of a component surface by building the whole component out of a high end material. The more cost effective way is to divide the material functional requirements between the surface and the core of the component by using a case composite material. Case material protects the component from wear, corrosion and the effects of light stress-gradients, while the base material provides the necessary strength and stiffness. A division of function becomes more acute where there is no base material that can cover the requirements, or when the surface and core requirements are so different that they cannot be achieved by one material." [1]

[1] H.J. Spies
     Optimierung des Gebrauchsverhaltens von Bauteilen durch Randschichtbehandlung
     Techn. Universität Bergakademie Freiberg, 26.-28.9.1995

ELTRO builds furnaces for nitriding, nitrocarbourising, oxidising and coating. Nitriding, nitrocarborising and
oxidising processing services are also provided at ELTRO heat treatment centres.

Hints for which coatings can be used for different demands can be found at http://www.randschichtverfahren.de