Collaborative Research: EAGER: Interactions Between Dislocations and Grain Boundaries in BCC Metals: Hall-Petch Effect

技术摘要：将构建一个包含大量离散位错影响的数值可处理的多尺度模型，并将其与基于电子后向散射衍射（EBSD）的新型表征进行比较，以解决长期存在的开放性问题：？为什么多晶金属的机械强度随晶粒大小而变化（霍尔-佩奇效应）？？该模型将避免任意长度尺度（应变梯度）和未观察到的微观结构（线性堆积）。相反，一种预测能力将被构建和测试。新的建模和表征能力将使材料设计和改进应用，例如金属成形，特别是体心立方金属，如钢。这些进展将被纳入两所参与大学的教学单元；本科生和研究生将接受研究实践方面的培训；EBSD灵敏度将提高两个数量级；结果将通过同行评审的出版物、论文和学位论文广泛传播。非技术概要：常见结构金属（如钢、铜、铝、钛）的强度随其微结构的大小而变化很大。例如，仅通过改变晶粒尺寸，钢的强度就可以提高10倍。目前还没有确定的机制或模型可以定量地预测这种众所周知的效应。为了便于设计和使用更好，更强的材料，一个预测的多尺度（微观/宏观）模型将被构建和测试使用新的分析技术。对这一重要效应的基本理解所带来的好处将允许生产和使用更好的材料，从而产生各种社会优势，如提高个人和国家安全，减少燃料消耗，减少温室气体排放。

Technical Summary:A numerically tractable multi-scale model incorporating the effects of large numbers of discrete dislocations will be constructed and compared with novel electron-backscattering diffraction (EBSD)-based characterization to address the long-standing open question: ?Why does the mechanical strength of polycrystalline metals vary with grain size (Hall-Petch Effect)?? The model will avoid arbitrary length scales (strain gradients) and unobserved microstructures (linear pile-ups). Instead, a predictive capability will be constructed and tested. The new modeling and characterization capabilities will enable material design and improve applications, e.g. metal forming, particular for body-centered cubic metals such as steels. The advances will be incorporated in instructional modules at the two participating universities; undergraduate and graduate students will be trained in research practices; EBSD sensitivity will be extended by up to two orders of magnitude; and results will be disseminated widely by peer-reviewed publications, theses, and dissertations.Non-Technical Summary:The strength of common structural metals (e.g. steel, copper, aluminum, titanium) varies greatly with the scale of its microstructures. For example, the strength of steel can be increased 10 times by changing the grain size alone. There is no confirmed mechanism or model that predicts this well-known effect quantitatively. In order to facilitate the design and use of better, stronger materials, a predictive multi-scale (micro/macro) model will be constructed and tested using new analytical techniques. Benefits of a fundamental understanding of this important effect will permit production and use of better materials, resulting in a variety of societal advantages such as increased personal and national safety, reduced fuel consumption, and reduction of greenhouse gas emissions.