Corrosion-resistant metallic coatings for applications in highly aggressive environments

Surface modification to improve the corrosion resistance of low-cost alloys is an economically attractive alternative to the use of expensive corrosion-resistant alloys. A low-grade steel surface modified by a suitable metallic diffusion coating can provide excellent corrosion resistance similar to that obtained with an expensive super alloy. We have used the fluidized bed reactor chemical vapor deposition (FBR-CVD) technique for the preparation of diffusion coatings containing Cr, Ni, Si and Ti on carbon and low-grade stainless steels. Several formulations of diffusion coatings on 409 SS have shown corrosion resistance similar to that of alloys AL6XN® or AL29-4C® in chemical heat pump applications. In this paper, we describe the preparation, characterization, and performance evaluation of a number of corrosion-resistant metallic diffusion coatings.