Determination of Youngʹs modulus and Poissonʹs ratio for coatings

Designing thin-film coatings to meet engineering needs requires the knowledge of accurate mechanical properties of the coatings. Youngʹs modulus and Poissonʹs ratio are two basic mechanical properties of materials, which should be conveniently measured. This paper reports a direct and non-destructive method for the measurement of the Youngʹs modulus and Poissonʹs ratio of a thin-film coating and its substrate based on the extended Hertz theory for the contact of coated bodies. The theory is used to analyze load–displacement data from a spherical indentation in the elastic range, in which the substrate effect is intrinsically modeled. The Youngʹs modulus and Poissonʹs ratio are determined at the same time through minimizing the difference between the measured and specially defined modified Youngʹs moduli. Two sets of validation experiments are also reported. This new method does not require any assumptions on pressure distribution and Poissonʹs ratio and can be easily incorporated into current indentation analysis systems.