Failure Mechanism Analysis and Life Prediction Based on Atmospheric Plasma-Sprayed and Electron Beam-Physical Vapor Deposition Thermal Barrier Coatings

Abstract

Using experimentally measured temperature-process-dependent model parameters, the failure analysis and life prediction were conducted for Atmospheric Plasma Sprayed Thermal Barrier Coatings (APS-TBCs) and electron beam physical vapor deposition thermal barrier coatings (EB-PVD TBCs) with Pt-modified -NiAl bond coats deposited on Ni-base single crystal superalloys. For APS-TBC system, a residual stress model for the top coat of APS-TBC was proposed and then applied to life prediction. The capability of the life model was demonstrated using temperature-dependent model parameters. Using existing life data, a comparison of fitting approaches of life model parameters was performed. The role of the residual stresses distributed at each individual coating layer was explored and their interplay on the coating’s delamination was analyzed. For EB-PVD TBCs, based on failure mechanism analysis, two newly analytical stress models from the valley position of top coat and ridge of bond coat were proposed describing stress levels generated as consequence of the coefficient of thermal expansion (CTE) mismatch between each layers. The thermal stress within TGO was evaluated based on composite material theory, where effective parameters were calculated. The lifetime prediction of EB-PVD TBCs was conducted given that the failure analysis and life model were applied to two failure modes A and B identified experimentally for thermal cyclic process. The global wavelength related to interface rumpling and its radius curvature were identified as essential parameters in life evaluation, and the life results for failure mode A were verified by existing burner rig test data. For failure mode B, the crack growth rate along the topcoat/TGO interface was calculated using the experimentally measured average interfacial fracture toughness.