Deposition of coatings containing Si and B on steels in a CVD fluidised bed reactor

Abstract

Diffusion coatings are frequently used to protect materials in various aggressive environments and in order to improve their surface properties. Fluidized bed technology (FBT) has been successfully used for the deposition of different types of diffusion coatings by a C.V.D. process, e.g. aluminizing, chromizing, nitriding, carburizing. On the other hand, very little information exists on boronizing or siliconizing using FBT, although the method is simple, efficient and environmentally friendly and the boride coatings have been reported to have an excellent combination of properties, e.g. high fatigue strength and wear resistance and the silicide coatings are well known for their excellent corrosion resistance. In this paper the results of a process of boronizing and siliconizing of steels via C.V.D. in a fluidised bed reactor are presented. Coatings of different thicknesses were obtained at temperatures below 1000°C. The coatings were analysed by means of optical microscopy, as well as by x-ray diffraction (XRD) and Vickers microhardness, in terms of the coating’s composition, morphology, thickness, hardness and phase formation. The boride coatings showed significantly improved tribological properties under dry wear conditions.