pounds are formed within the diffusion layer, they may produce diffusion barriers or create brittle effects. Chromising has been practised as a highMost modern diffusion coatings are basically descendtemperature thermochemical diffusion coating process, primarily on steels but also on nickel and ants of traditional carburising and nitriding processes, cobalt based superalloys, for many years. The which have been used for at least 200 years, originally large accumulation of data in the literature relating as an art rather than a science. The origin of diffusion to both theory and industrial usage is reviewed.bonding can probably be found in ancient Egypt, Thermodynamic and kinetic approaches are relating to gold cladding on copper substrates. Conconsidered together with the coating thickness and sidering that metallic chromium became available structure required for high temperature protective only in 1789, all chromising operations are necessarily applications.IMR/311 more recent developments.

A study has been made of the structure of chromised coatings on a 11%Cr steel paying special attention to the character of M 23 C 6 formed and the diffusion controlled rate of formation. Values of diffusion coef®cients derived are given, and typical X-ray intensity values tabulated for the major diffraction planes found in the transitional chromised iron layers.MST/4458