CAREER: Controlling Pressure-Induced Transformation in Rare Earth Orthophosphates

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NON-TECHNICAL DESCRIPTION: Sudden through to slowly growing cracks in high temperature ceramic components such as combustors, nozzles, and thermal insulation in aircraft engines, turbines, and rockets can lead to catastrophic failure. Some unique ceramics undergo a change in their shape and volume to a new crystal structure when they are deformed, which can be harnessed to impart increased toughness in a material by absorbing energy caused by an impact or propagating crack. This project is determining how to use chemistry to control the point at which the change to a new crystal structure occurs and its speed of transformation. The information and new materials discovered in this research can be useful in designing fiber coatings for ceramic matrix composites with better performance (superior mechanical properties) for high temperature aerospace applications. Both undergraduate and graduate students in Materials Science and Engineering are being trained and mentored. This project is developing science learning modules for use by local elementary school teachers from school districts with a high percentage of minority students and the Rocky Mountain Camp for the Dyslexic. These complementary education and outreach components broaden the participation of underrepresented groups in science and engineering in an effort to meet the U.S. need for expanding the science and technology workforce with more highly qualified people. This project will help strengthen U.S. innovation and economic competitiveness in the area of turbine engines and in terms of education.TECHNICAL DETAILS: This project is establishing the influence of chemistry, grain size, temperature, and stress state on pressure-induced phase transformation kinetics in rare earth (RE) orthophosphate ceramics (REPO4 crystal structure). Phase transformations in these materials are being examined using a range of techniques that include high-temperature nanoindentation, transmission electron microscopy, and diamond anvil cell (combined with Raman spectroscopy). One goal is to enable precise control over the trigger for the plasticity transformation in coatings for improved ceramic matrix composites. The influence of kinetic effects on the transformation onset pressure and degree of reversibility are being identified. Insights gained through this research are aiding in the science-based design of ceramic composites, components, and devices in which pressure-induced transformation must be triggered with precise timing for maximal effect. This work addresses a grand challenge of the field to understand the factors controlling phase transformation kinetics that can lead directly to new ways to process metastable materials with enhanced functionality.