Mechanisms of Toughening Structural Ceramics by Thermal Engineered Laser Shock Peening

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With their combination of heat resistance, wear and corrosion resistance, and high compressive strength, structural ceramics are ideal candidates for many critical aeronautic, automobile, refractory, and nuclear applications. However, the fracture toughness of ceramics is very low compared to metals, which reduces the mechanical reliability. The inability to toughen ceramics has limited their use in critical engineering applications. This award supports research which aims to address this critical gap in knowledge by applying to ceramics a laser processing technique originally devised for metals, to improve the low fracture toughness and crack sensitivity. This research has the potential to lead to the widespread use structural ceramics in a variety of applications such as cutting tools, turbine engines, and armor. The research team will promote engineering education through outreach programs such as "Sunday with a Scientist" presentations at the University of Nebraska State Museum, and the partnership with the McNair Scholars Program to train undergraduate researchers from underrepresented groups. The goal of this research is to improve the low fracture toughness and crack sensitivity of structural ceramics by inhibiting surface-originated crack propagation using a thermally engineered laser shock peening process. To fulfill the research goal, four objectives will be completed to (1) develop the process for performing thermally engineered laser shock peening on ceramics; (2) assess the residual stresses and mechanical properties of ceramics following laser shock peening; (3) reveal the microstructure-property relationship of ceramics in the laser shock peening process; and (4) identify the mechanisms by which laser shock peening toughens ceramics. The team will apply this process to a variety of structural ceramics and measure their residual stresses and fracture toughness. The microstructural evolution of the ceramics will then be characterized using transmission electron microscopy and focused ion beam techniques. The toughening mechanisms will be identified through modeling and ex-situ and in-situ electron microscopy methods. This work will provide new fundamental knowledge of the processing-microstructure-property relationships in ceramics with respect to the laser shock peening process. In addition, the results will advance the field by shedding light on the mechanism of toughening ceramics by controlling the residual stress state and microstructural changes.