The Mechanism of Rapid Interdiffusion Bonding During Air Plasma Spraying of Thermal-Environmental Barrier Coatings for Future Ceramic Turbine Components

Previously, we have demonstrated despite an abnormally high CTE mismatch for a MultiLayered ceramic coating system, that it is possible under certain circumstances to fabricate zirconia-based thermal barrier oxides atop rare-earth disilicate environmental barrier coatings. Past results have demonstrated these thermal-environmental barrier coatings (T-EBCs) are not only durable upon fabrication, but also withstand thermal shock both in isothermal as well as thermal gradient conditions. To date, there have been only hypotheses presented for the exact mechanism governing this surprisingly-enhanced bonding mechanism between 8YSZ and Yb₂Si₂O₇. This presentation will demonstrate, through multiple ultrahigh resolution characterization methods: FIB-SEM, STEM/EDS, EBSD, and Atom Probe Tomography, the mechanism that takes place during initial fabrication of 8YSZ thermal barrier coatings atop amorphous Yb₂Si₂O_7­ environmental barrier coatings. The counter example of plasma-spraying 8YSZ atop crystalline Yb₂Si₂O_7­ will also be shown, for reference, to demonstrate the what has inhibited past research from successfully fabricating such T-EBCs. The results from these unique characterization techniques all converge on a single conclusion: nano-scale interdiffusion reactions take place at the microsecond timescale during rapid solidification of the molten 8YSZ droplets – forming a chemical bond between the 8YSZ and Yb₂Si₂O₇ that exceeds traditional mechanical interlocking adhesive strengths of thermally sprayed coatings.