Deposition of Cr, Al coatings on Ni by means of a PB and FB CVD process

Abstract
The present work concerns the formation of chromium and/or aluminide diffusion coatings on nickel, by means of a pack and fluidised bed chemical vapour deposition (PBCVD and FBCVD) process. The object to be treated is suspended within the reactor, which contains the treating agent. The latter is a mixture of powders of the donor of the coating-forming element (Al, Cr, Al-Cr) and of a filler material (Al₂O₃). As an activator of the process, a halide compound is used (NaCl, NH₄Cl, NaCl + NH₄Cl, HCl) in an inert atmosphere (Ar). The precursor vapours of the element to be deposited are formed in situ, by the reaction of the donor with the activator and react with the substrate surface for the formation of the coatings. The produced coatings are characterised by optical microscopy and SEM techniques (EDS) , in order to obtain their surface composition, the coating thickness and quality and the aluminium and chromium distribution along the coating-substrate interface. The formation of Al-Cr diffusion coatings was achieved in a short time PB and FB process, accompanied by a clearly visible diffusion zone.