Constrained sintering of glass, glass–ceramic and ceramic coatings on metal substrates

Many applications now use different materials that are fabricated into structures to obtain the desired combination of properties or to suit particular needs. Ceramics and glasses often are combined with metallic materials for applications in the field of electronics, for insulation and chemical resistance and for improved structural performance such as in composites. One common method of fabricating such structures is by firing coatings and films onto substrates. To obtain usable and reliable components several issues need to be addressed. Two of them—the effect of constraint on the densification and interfacial adhesion—are addressed in this paper. Measurements of densification of some glasses and ceramics showed that the densification rate is reduced by substrate constraint and the effect is more pronounced on crystalline materials than glass. Good adhesion between the coatings and metal substrates also required modifications to the substrate surface to enhance bonding. For coatings sintered onto substrates, such modifications resulted in better bonding. Good adhesion between borosilicate glass and stainless steel was obtained by roughening and preoxidation of the substrate. A very strong adhesion also was obtained between cordierite glass–ceramic and molybdenum substrate after depositing chromium/nickel or chromium/copper layers on the substrate as adhesion layers before coating.