Measurement of the adhesion of a brittle film on a ductile substrate by indentation

The indentation of a brittle film on a ductile substrate is analysed for obtaining the interface toughness. This measurement method of adhesion provides a simple technique for sampling a small area of the interface on practical geometries with common laboratory equipment. Mechanics solutions are presented to access the interface toughness, $\Gamma _{\text{c}}$, from measurements of the applied load, delamination radius, film thickness and film-substrate material properties. The test is found to be particularly effective for films under large residual compression. Measurements of the interface toughness ($\Gamma _{\text{c}}\sim $ 45 J m$^{-2}$) are made for a diamond-coated titanium alloy.