The role of silicon in corrosion-resistant high temperature coatings

Besides aluminium and chromium, silicon is one of the most favourable protective scale-forming or scale-modifying elements. An attempt is made to outline the present fundamental understanding of the role of silicon in scale formation and scale maintenance on refractory metals and high temperature alloys. Various coating concepts are discussed ranging from brittle silicide coatings to modified MCrAlY overlayers and composite structures with dispersed silicide reservoirs in ductile matrices. The latter appear to be the most promising candidates for gas turbine applications to overcome the problems of inherent brittleness, spalling and interdiffusion effects. On the basis of results from laboratory tests and engine experience the beneficial effect of silicon in oxidation, hot corrosion and to some extent carburization is demonstrated.