Determination of coating mechanical properties using spherical indenters

In recent years, various forms of indentation testing have been increasingl y used to determine the material properties of specimens. This technique, p articularly the nano-indentation method, has been extended to the testing o f coating systems in order to calculate the individual properties of the th in coatings and the substrates. However, thr: interpretation of the test da ta to achieve this is complex and continues to be a widely studied subject. Based on the finite element analysis (FEA) of coated surfaces indented by a spherical indenter, this paper describes methods for combining FEA and ex perimental indentation testing to determine coating modulus and hardness in dependent of substrate effects. An indentation test on a coated specimen is first carried out using a spherical indenter. The combined contact modulus of the coated surface is determined from the elastic portion of the experi mental load/displacement curve. The modulus of the coating alone is then co mputed from a function derived by a parametric finite element analysis of i ndentation behaviour. The hardness of the coating alone is determined by co mparing the experimentally determined mean contact pressure with parametric finite element results for the same contact geometry and known hardness ra tios. Using this proposed methodology, the properties of the substrate are fully taken into consideration, hence providing a more universal and accura te measurement of coating elastic modulus and hardness. (C) 1999 Elsevier S cience S.A. All rights reserved.