Adhesion Strength of Cordierite Bulk Coatings on Molybdenum Substrates

Cordierite was adhered to molybdenum using various metallic interlayers of copper, nickel, and chromium. The development of a coating adhesion test methodology was required to choose between interface designs. An indentation method was chosen because of ease in testing and availability of fracture mechanics interpretations of test data. The interfacial fracture toughness was determined from indentation load vs. crack length data by examining the residual stress and critical buckling load of the ceramic coatings. The interfacial fracture toughness values obtained using a slightly different indentation analysis agree with those in the literature. Quantitative chemical analysis of the interface microstructure was used to explain differences in interfacial fracture toughness values for samples with different metallic interlayer designs. The best interface design for adhering cordierite glass-ceramic coatings to molybdenum was found to be molybdenum / 2 μm copper / 4 μm chromium / cordierite.