Residual stress evaluations of thermal spray coatings by a modified layer removal method

Residual stresses are inherent in thermal spray coatings because the application process involves high temperature gradients on materials with different mechanical properties. Failure analysis of thermal spray coatings has, in many cases, pointed to residual stresses as a factor contributing to reduced service life. Therefore, it is of interest to evaluate residual stresses in thermal spray coatings. An established method for experimentally evaluating residual stresses is the layer removal method. While the method offers several advantages, applications are limited to a single material system and do not include coated materials. This paper describes a modification to the layer removal method to handle coated materials. The modification is validated by comparisons with finite element analysis results. The modified layer removal method was then applied to determine through-thickness residual stress distributions for the following six industrial coatings; stainless steel, aluminum, Nickel-5 Aluminum, two tungsten carbides, and a ceramic thermal barrier coating. Advantages of the method are that it (1) requires only ordinary strain gauge measuring equipment and (2) is not very sensitive to uncertainties in the mechanical properties of the coating material.