Influence of the Interfacial Roughness on Residual Stress Analysis of Thick Film Systems by Incremental Hole Drilling

Abstract

Thick film systems with coating thicknesses between 50 and 1000 µm are often fabricated by thermal spray processes. During the deposition and due to the substrate pre-treatment residual stresses, which influence the coating properties, develop. Due to the substrate preconditioning thermal spray coatings exhibit a large interfacial roughness. This study investigates the application of the incremental hole-drilling method on thermal spray coatings. The focus is on the influence of the interfacial roughness on the residual stress evaluation. A systematic FE-study was carried out in order to minimize the final error for the residual stress evaluation. The simulation results are transferred to experimental hole-drilling results of a thermally sprayed model thick film system. Finally, the hole-drilling results are compared to the residual stress depth profile that was determined by X-ray diffraction in combination with successive electrochemical layer removal. The results clearly show that the effect of the interfacial roughness can be neglected for residual stress calculation if the mean coating thickness is properly considered for calculation of the calibration function / parameters.