Mechanisms of Toughening Structural Ceramics by Thermal Engineered Laser Shock Peening

结构陶瓷兼具耐热性、耐磨性、耐腐蚀性和高抗压强度，是许多关键的航空、汽车、耐火材料和核应用的理想候选者。然而，与金属相比，陶瓷的断裂韧性很低，这降低了机械可靠性。陶瓷无法增韧，限制了它们在关键工程应用中的应用。该奖项支持旨在通过将最初为金属设计的激光加工技术应用于陶瓷来解决这一关键知识缺口的研究，以改善陶瓷的低断裂韧性和裂缝敏感性。这项研究有可能导致结构陶瓷在各种应用中的广泛应用，如刀具、涡轮发动机和装甲。研究团队将通过外展项目促进工程教育，例如在内布拉斯加州大学州立博物馆举办的“周日与科学家同行”演讲，以及与麦克奈尔学者项目合作，培训来自代表性不足群体的本科生研究人员。本研究的目的是通过采用热工程激光冲击喷丸工艺抑制表面裂纹的扩展，从而改善结构陶瓷的低断裂韧性和裂纹敏感性。为了实现这一研究目标，将完成四个目标：(1)开发对陶瓷进行热工程激光冲击喷丸的工艺；(2)评估激光冲击喷丸后陶瓷的残余应力和力学性能；(3)揭示激光冲击喷丸过程中陶瓷的组织-性能关系；(4)确定激光冲击喷丸增韧陶瓷的机理。该团队将把这一过程应用于各种结构陶瓷，并测量它们的残余应力和断裂韧性。然后，将使用透射电子显微镜和聚焦离子束技术来表征陶瓷的微观结构演变。增韧机理将通过模拟、非原位和原位电子显微镜方法来确定。这项工作将为激光冲击喷丸过程中陶瓷的加工-显微组织-性能关系提供新的基础知识。此外，通过控制陶瓷的残余应力状态和微观结构的变化，这一结果将有助于揭示增韧陶瓷的机理。

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.