Measuring the adhesion of sol–gel derived coatings to a ductile substrate by an indentation-based method

The adhesion of sol–gel derived coatings to underlying substrates is a critical parameter. However, measuring the adhesion can be very difficult because such coatings have low cohesive strength and are brittle. In this study, an indentation-based method was used to measure the adhesion of sol–gel derived coatings to ductile substrates. A diamond Rockwell C indenter was driven through a sol–gel coating and into the underlying substrate. Extensive plastic deformation of the substrate caused an annular crack to develop at the coating–substrate interface. A microindentation technique was developed to measure the radius of the annular crack. The interface toughness was then calculated from the crack radius value, along with coating thickness, residual stress and mechanical properties of the coating and substrate.