Collaborative Research: Plastic Ceramics: The Role of Grain Boundaries During Laser Shock Peening

NON-TECHNICAL DESCRIPTION: Laser shock peening (LSP) is a new surface engineering method that has been proven to prevent crack growth in several ceramic materials, which are inherently brittle. In particular, success has been found with ceramics suitable for applications in extreme environments (e.g., hypersonic vehicles, gas-turbine engines, and armor). The general applicability of this technique is impeded because the underlying mechanisms are not fully understood. The goal of this project is to identify the role internal interfaces play during LSP to guide future material design, which will extend the applicability of this technique and increase its effectiveness at improving the ceramics’ mechanical performance. The next generation of ceramic engineers are being trained on these methods and approaches to enable the processing and implementation of tough structural ceramics. In addition to the two doctoral students, undergraduate and high school students are being recruited to participate in the project each summer. TECHNICAL DETAILS: This research identifies how grain boundary character (macroscopic parameters, thickness, and chemistry) in ceramics affects the propensity to form dislocations and, thus, build compressive residual stresses during LSP. LSP has been adapted to ceramic materials such as silicon carbide and alumina to induce compressive residual stresses that improve their crack resistance. Yet, the fundamental mechanisms and the broad applicability of the technique remain poorly understood. The scientific hypothesis is that LSP will be applicable to materials with higher order complexions – equilibrium grain boundary states with high disorder – to generate shock wave propagations that initiate dislocation formation necessary for building compressive residual stresses near grain boundaries. To test this hypothesis, the effect of LSP is being investigated in various grain boundaries of different character and composition in alpha-phase alumina with complexion engineering. The specific aims are to (1) correlate the extent of compressive residual stress induced by LSP with grain boundary character distributions and grain size and (2) identify individual grain boundary structures associated high dislocation density. Engineering students are learning valuable skills in ceramic processing and electron microscopy characterization. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.