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

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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.