User Program study with E. Jordan of University of Connecticut
| Residual stress is
a source of strain energy that can promote spallation of a coating.
Thermal barrier coatings (TBCs) are typically fabricated using either
air plasma spray or electron-beam physical vapor deposition processing.
Due to the high temperatures associated with thermal spray processes
and differences in coefficients of thermal expansion between the
coatMicrostructure of the solution precursor plasma spray TBC coatings. material and the substrate material, residual stresses in the coating are unavoidable. Recently, a novel solution precursor plasma spray method was employed at the University of Connecticut to produce high-quality TBCs. However, the process results in a microstructure (Fig. 5-12) that has through-thickness stress-relieving cracks. Such cracks are expected to yield unusually low residual stress. The superior durability of these coatings has been attributed to these anticipated low residual stresses. Therefore, it was important to determine the residual stress level in the TBCs. Researchers visited the RSUC X14A synchrotron beam line facilities at the NSLS to take advantage of the parallel X rays and excellent angular spatial resolution. An XRD/layer-removal technique was used to characterize the residual stress depth profile in YSZ solution-precursor plasma-spray TBCs. Several samples were examined, and near-zero residual stress throughout most of the coating thickness was confirmed. Near the coating/bond coat interface (within ~10 microns), the YSZ showed an in-plane compressive residual stresses of ~100 MPa.  |
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Acknowledgments
URL: http://www.html.ornl.gov/duc/tisic.html