| About this Abstract |
| Meeting |
MS&T22: Materials Science & Technology
|
| Symposium
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ACerS Robert B. Sosman Award Symposium: Advancing the Science of Materials for Extreme Environments
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| Presentation Title |
Exploring Why Ultra-high Temperature Ceramic Ceramics Work in Extreme Environments |
| Author(s) |
Laura Silvestroni, Nicola Gilli, Jeremy Lee Watts, William G. Fahrenholtz |
| On-Site Speaker (Planned) |
Laura Silvestroni |
| Abstract Scope |
The latest generation UHTCs, based on a borides and sintered in the presence of transition metal (TM) compounds, has demonstrated strengths beyond current benchmark ranges. Peaks of ~1 GPa were achieved at 1800°C and strength remained above 400-600 MPa up to 2100°C. Upon exploration of the microstructural features by TEM, a unique multi-scale microstructural arrangement was discovered. The TM, partially dissolved into the boride matrix during sintering, led to the formation of a core-shell grain structure characterized by dislocation networks and polygonised dislocation walls. Particularly, the shell was found to be a super-saturated solid solution in which nano-particles precipitated. These were rounded metallic W droplets or elongated and oriented TaC needles, when WC or TaSi2 additives were introduced, respectively.
This complex hierarchical microstructure, featured by several levels of spatial variations and resulting in an improved combination of strength and ductility is thought to be responsible for the elevated temperature strengthening. |