Understanding the Role of Residual Stress Gradients on Plastic Strain Recovery in Nanocrystalline Thin Films

该奖项支持研究以确定纯纳米晶金属薄膜中控制塑性应变恢复的微观机制。该项目将实施综合实验和建模策略来实现这一目标。识别控制塑性应变恢复的机制将提高设计变形或凹痕后可恢复的金属部件的可能性。这些基础知识将用于开发预测工具，这将有助于准确预测生命，以减少过早失效。燃气轮机和摩擦涂层等多种应用都可以从这些发展中受益。此外，该项目还将通过计算力学和显微镜领域的研究生和本科生教育，为未来和多元化的劳动力提供一个综合培训平台。在这方面一个特别有趣的活动是与当地社区学院的合作，该学院的学生将能够申请为期8周的研究实习。纳米晶金属的变形行为与粗晶金属的变形行为有很大不同。其中一种独特的行为是纳米晶金属恢复塑性应变的能力。这种现象非常不寻常，因为金属的塑性变形在卸载后被认为是永久性的。然而，关键的微机械驱动力尚不清楚，仍然是猜想的主题。因此，微观结构敏感的预测建模框架仍然难以实现。这项工作的具体目标是：（1）确定纳米颗粒弹性响应失配对塑性应变恢复的影响； (2)阐明织构对残余应力的影响； (3)识别晶界滑动与应变相容性之间的联系； (4)确定晶界滑动对残余应力梯度的影响。为了实现这些目标，制定了综合实验建模计划，其中包括使用先进的显微镜技术（例如扫描透射电子显微镜）和复杂的弹塑性相场建模方法进行广泛的原位测试和表征。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力优点和更广泛的影响审查标准进行评估，被认为值得支持。

This award supports research to identify the microscopic mechanisms governing plastic strain recovery in pure nanocrystalline metal thin films. This project will implement an integrated experimental and modeling strategy to address this objective. The identification of the mechanisms governing plastic strain recovery will raise the possibility of designing metal components that may recover after being deformed or dented. This fundamental knowledge will be used to develop predictive tools, which will facilitate the accurate prognosis of life to mitigate premature failures. There is a wide range of applications such as gas turbines and tribological coatings among others that can benefit from these developments. In addition, the project will provide an integrated training platform for the future and diverse workforce via the education of graduate and undergraduate students in the areas of computational mechanics and microscopy. A particularly interesting ativity in this regard is the partnership with a local community college, whose students will be able to apply for 8-week long research internships.The deformation behavior of nanocrystalline metals substantially differs from that of coarse-grained metals. One such unique behavior is the ability of nanocrystalline metals to recover plastic strain. This phenomenon is quite unusual since plastic deformation in metals is considered permanent after unloading. The critical micromechanical driving forces are not clear however and remain a subject of conjecture. As a result, a microstructure-sensitive predictive modeling framework also remains elusive. Specific objectives of this work are to: (1) identify the influence of mismatch in elastic response of nano-sized grains on plastic strain recovery; (2) elucidate the influence of texture on the residual stresses; (3) identify the connection between grain boundary sliding and strain compatibility; and (4) identify the influence of grain boundary sliding on the residual stress gradients. An integrated experimental-modeling plan is put in place to achieve these objectives that includes extensive in-situ testing and characterization using advanced microscopy techniques, such as the scanning transmission electron microscopy, and sophisticated elastoplastic phase field modeling method.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.