Comparison of surface and cross-sectional indentation in a coating

Surface and cross-sectional indentation of an oxide scale are compared in order to gain insight into the mechanical behaviour of coatings. The dependence of the elastic modulus and hardness on the ratio of indentation diameter to layer thickness was determined. It is shown that cross-sectional indentation can be used as a complementary method to assess coatings. Due to the high compressive in-plane residual stresses indentation in the surface did not result in radial cracks. Cross-sectional indentation resulted in cracks parallel to the interface, whereas no cracks formed in the direction perpendicular to the interface between coating and substrate. An assessment of the fracture toughness appears to be possible for cross-sectional indentation if the indentation pressure as a measure of the apparent hardness is incorporated into the relevant relationship, thereby taking into account the softer surrounding materials.