Measuring and Modeling Residual Stresses in Air Plasma Spray Thermal Barrier Coatings

Abstract

Thermal barrier coatings (TBC) consisting of an MCrAlY bond coat and a yttria-stabilized zirconia top coat have been extensively used to increase operating temperature and improve component durability in aircraft and industrial gas turbine engines. Residual stresses are induced in thermal barrier coating during deposition and play an important role in TBC performance in service. The residual stresses are attributed to droplets quenching and secondary cooling from deposition temperature to room temperature. In this study, 1.1-mm thick TBC specimens were prepared by air plasma spray. Residual stress was measured using the synchrotron light source method. A 92.6-kV high-energy x-ray (HEXRD) beam 0.030 mm high x 1.5 mm wide was applied on the cross section of TBC samples. The crystal lattice distortion of TBC due to residual stresses was measured in all directions. The residual strains and stresses were calculated from measured data. The results showed compressive radial residual stress in TBC. The compressive residual stress was higher at TBC/bond coat interface and at TBC free surface. The residual stresses in TBC and bond coat were predicted using T-CLIP software. In-plane residual stress in TBC was measured in compressive nature in the range of -37 to -120 MPa. There is good agreement between measured stress and predicted stress level after sample cooling from steady process temperature to room temperature. The quench stress, which predicted high tensile stress, did not show in the TBC. The factors that effect residual stresses in TBC were discussed in this paper.