Evaluation Method of the Residual Stresses in Thermal Barrier Coating System Based on the Curvature of the Three-Layered Specimen

Abstract

A thermal barrier coating (TBC) system consists of a TBC topcoat (TC), a bond coat (BC), and a substrate. Residual stress acting on a coating is a important parameter for materials mechanics and hence need to be evaluated. We propose a simple method for evaluating the residual stresses acting on each layer of a TBC system by using a curvature method. First, a three-layered model was constructed based on the misfit strain between the coatings and the substrate. This method uses the curvatures of the substrate with a blast treatment, the BC system specimen with the blast and BC, and the TBC system specimen with the blast, BC, and TC instead of a change in curvature during thermal spraying. Next, the residual stresses acting on the TBC system specimen with varying thicknesses were evaluated by using the proposed method. It was confirmed that the proposed method provides reasonable residual stresses in the BC and TC. Finally, the thermal stress after the coating deposition was theoretically evaluated, and the quenching stress of the coating during the deposition was evaluated by using the difference between the experimentally determined residual stress and the theoretical thermal stress. The mechanism for generating the residual stress in the TBC system during thermal spraying was investigated using the quenching stress and thermal stress.

Thermal‐cycle dependent residual stress within the crack‐susceptible zone in thermal barrier coating system

“…Several types of experimental techniques have been used for the measurement of residual stress in TBC systems. The methods based on curvature change, layer removal, and hole drilling are only capable of obtaining average stress, which is insufficient for analysis of microcracks driven by local stress, and moreover, they are either destructive or invasive . The nanoindentation method can be used to measure local stress, but its intrusiveness of tested sample limits its application.…”

“…The methods based on curvature change, layer removal, and hole drilling are only capable of obtaining average stress, which is insufficient for analysis of microcracks driven by local stress, and moreover, they are either destructive or invasive. [7][8][9][10] The nanoindentation method can be used to measure local stress, 11 but its intrusiveness of tested sample limits its application. The 2D/3D digital image correlation method has the advantages of mapping full-field stress distribution, 12,13 but it has great uncertainty to define the initial stress state and to process the images.…”