Corrosion protection of an AISI 321 stainless steel by SIC coatings

Silicon carbide coatings were produced by dynamic ion mixing (DIM) at room temperature and at 750 degrees C by ion beam sputtering of a SiC target and simultaneous bombardment with a 160 keV Ar+ ion beam. The chemical composition of the coatings was determined by Rutherford backscattering and by nuclear reaction analysis. The microstructural state of the coatings was investigated by high resolution transmission electron microscopy whereas their density was determined by X-ray reflectometry. It is found that, for all the deposition temperatures, the DIM treatment promotes the crystallisation of the beta-SIC phase. Passivation/corrosion tests performed in 1 N H2SO4 indicate that the corrosion resistance is considerably improved by DIM regardless of the deposition temperature. It is suggested that the interface mixing along with the coating densification is responsible for the protective effect. (C) 1998 Elsevier Science S.A.