 |
| Research Focus & Application: |
| |
Thermal barrier coatings are material systems applied to metallic surfaces, such as in turbine or aero-engine parts, operating at high temperatures. These coatings serve to insulate metallic components from large and prolonged heat by utilizing thermally insulating materials which can sustain a high temperature difference between the load bearing alloys and the coating surface. In doing so, these coatings can allow for higher operating temperatures while limiting the thermal exposure of structural components, extending part life by reducing oxidation and thermal fatigue.
These coatings typically consist of four layers. They are the metal substrate, metallic bond coat, thermally grown oxide, and ceramic topcoat(i.e Zirconia). The metal substrate and metallic bond coat are metal layers and the thermally grown oxide and topcoat are ceramic layers. The metal substrate is typically a high temperature alloy.
Many parameters are of importance for proper protection and operation. A few typical applications in quality control and failure analysis using optical microscopy are: layer thickness measurement, percent porosity and crack identification.
| Microscopy and Imaging Methods: |
| |
AxioImager M1m microscope with Brightfield, C-DIC and Polarized light along with Axiovision Digital Imaging Software and automated layer thickness module. | |
Thermal barrier coating on Nickel Alloy. Airfoil cross section, mounted and polished: C-DIC contrast with 10x EC Epiplan Neofluar objective.
Thermal barrier coating on Nickel Alloy . Airfoil cross section, mounted and polished (same sample as C-DIC image): Polarized light contrast with 10x EC Epiplan Neofluar objective. Polarized light can provide very high contrast of top layer (Zirconia) to surrounding materials for easy automated layer thickness measurement (red lines perpendicular to coating surface). |