Measurement of Young’s modulus and Poisson’s ratio of thin coatings using impact excitation and depth-sensing indentation

Poisson’s ratio is important for the characterization of coatings, as it is needed to determine the mechanical properties of coatings using techniques such as depth-sensing indentation and surface acoustic wave spectroscopy. However, until now it has been extremely difficult to measure the Poisson ratio of a coating and it is commonly assumed, often incorrectly, that it is the same as that of the bulk material. A new technique has therefore been developed following recent developments in impact excitation and depth-sensing indentation to measure the Poisson ratio of coatings. Impact excitation was first used to determine the Young modulus of the coatings. These results were then used in combination with the plane strain modulus obtained from depth-sensing indentation to determine the Poisson ratio of the coating. This technique has been successfully applied to determine the Poisson ratio of sputter deposited TiN coatings up to 2.66 μm thick. Consistent values of Young’s modulus (427±9 GPa) and Poisson’s ratio (0.23±0.03) were obtained for all the coatings, which agree with literature values for similar but thicker coatings obtained using acoustic microscopy.