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

非技术描述：激光冲击喷丸(LSP)是一种新的表面工程方法，已被证明可以防止几种固有脆性的陶瓷材料中的裂纹扩展。特别是，陶瓷已经成功地应用于极端环境(例如，高超声速飞行器、燃气轮机和装甲)。这项技术的普遍适用性受到阻碍，因为其潜在的机制还没有完全被理解。本项目的目标是确定内部界面在LSP过程中所起的作用，以指导未来的材料设计，从而扩大该技术的适用范围，提高其在改善陶瓷力学性能方面的有效性。下一代陶瓷工程师正在接受这些方法和途径的培训，以实现坚韧结构陶瓷的加工和实施。除了两名博士生外，每年夏天都会招募本科生和高中生参与该项目。技术细节：这项研究确定了陶瓷中的晶界特征(宏观参数、厚度和化学成分)如何影响位错的形成倾向，从而在LSP过程中形成压缩残余应力。LSP已被用于碳化硅和氧化铝等陶瓷材料，以产生压缩残余应力，从而提高它们的抗裂性。然而，这项技术的基本机制和广泛的适用性仍然知之甚少。科学假设是，LSP将适用于具有更高顺序络合的材料--具有高无序的平衡晶界状态--以产生冲击波传播，从而启动在晶界附近形成压缩残余应力所必需的位错形成。为了验证这一假说，我们用相变工程方法研究了LSP在不同性质和成分的α-氧化铝晶界中的作用。其具体目的是(1)将LSP引起的残余压应力的大小与晶界特征分布和晶粒度相关联，以及(2)确定与高位错密度相关的单个晶界结构。工程学学生正在学习陶瓷加工和电子显微镜表征方面的宝贵技能。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.