Evaluating Mechanical Properties of Hard Coatings by Using Relativity Method

Mechanical properties of coatings are usually affected by the substrate behavior and the thickness of the coating. The film on a substrate can’t be tested like a monolithic sample. Therefore, the absolute value of the mechanical properties of the film is often difficult to obtain, but the properties of a coated sample and a monolithic sample could be measured, and there must be a unique relation between them. Based on this consideration, a relativity method was proposed to evaluate the mechanical properties of coatings, including the hardness, elastic modulus. Satisfactory results have been obtained from the experiments using this clue. Moreover, residual stresses caused by mismatch of the coefficients of thermal expansion between the coating and substrate was calculated based on the uneven strain mode, it indicates that the interfacial shear stress concentrated at edges and maximum stress in coating is at the center.