Analysis of residual stresses in thermal barrier coatings

Stabilized zirconia coatings are used as thermal barrier coatings (TBCs) be cause of their ability to improve the performance and efficiency of gas tur bine engines by allowing higher turbine inlet temperature and reduced cooli ng air flow. Yttria stabilized zirconia plasma sprayed coatings (PS top coa ting) were applied on high temperature Ni-based alloys pre-coated with a th in, dense stabilized zirconia coating produced by Physical Vapour Depositio n (PVD bond coating). This contribution concerns the residual stress analys is of a TBC coating system. The coating residual stress was studied experim entally (by X-ray diffraction, micro-Raman techniques and microdisplacement laser transducer) and numerically in the thermal barrier multi-layered sys tem for the as-deposited coatings after different thermal cycling processes . The PVD bond coating has an in-plane compressive residual stress after de position (about -320 MPa). The plasma sprayed top coating has a compressive stress near the interface and presents low tensile (or compressive) stress on the surface after plasma spraying deposition (-20 to 30 MPa, depending on the substrate temperature and coating thickness). After thermal cycling, the stress changes to -760 MPa for the PVD bond coat and the PS coating st ress changes to a compressive value of about -300 MPa. The stress within th e Cr2O3 scale was -1680 MPa, as determined by micro;Raman spectroscopy The residual stresses within the TBC during thermal cycling were modelled, the numerical results being in good agreement with the experimental measurement s. (C) 1999 Elsevier Science S.A. All rights reserved.