A Fundamental Study of Flow Mechanisms in Nanostructured Al Alloys and Intermetallic Compounds

非技术摘要：轻质铝（Al）具有高强度，但在应力下充分变形而不断裂的生产在技术上具有挑战性的制造，以加速其在汽车和航空航天工业中的应用。早期的研究表明，通过高压和扭转（扭转）的组合，通过严重的永久变形，显着的显微组织细化导致块体金属具有优异的硬度。因此，本项目的目标是科学地研究如何在显微组织细化过程后在常规铝合金和金属间化合物中实现高强度和良好的断裂伸长率。本项目的重要性在于了解纳米结构铝系统在高压和扭转处理后的强化和流动机制，并确定如何克服块体纳米结构铝合金及其化合物的强度和成形性的矛盾。这些结果预计将有一个重要的积极影响，因为机械的理解，提高散装金属的机械性能将提供新的机会，为铝合金的应用和轻质工程材料的选择策略的发展。该研究需要精通物理学、材料科学和机械工程等多个领域，这对本项目支持的研究生和本科生来说是一个挑战，也是一个回报。技术摘要：在铝合金和金属间化合物中，同时实现高强度和良好的延展性是目前无法控制的。虽然通过高压扭转（HPT）进行晶粒细化通常可以提高金属的硬度，但在金属材料中实现高强度和延展性的策略仅在有限的条件下可用：在沉淀硬化合金或含有高密度纳米孪晶的材料中。除了在可时效硬化的组合物中之外，将那些引入具有高堆垛层错能的Al系统中是一个主要挑战。因此，本项目的目标是了解在微观和宏观尺度上的超细微观结构的强化和塑性的塑性流动机制，并设计策略，以提高HPT处理的超细晶Al系统的强度和延展性。该项目将纳米晶材料冶金研究的专业知识与先进的纳米压痕技术和最先进的X射线和电子衍射分析测量表征方法相结合。这些技术允许识别复杂的金属流动与并发的纹理变化在环境温度和升高的温度下的时间尺度。该项目的贡献是重要的，因为所获得的改善大块金属机械性能的科学知识可以扩展到广泛的多晶材料，该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准。

Non-technical Abstract:The production of lightweight aluminum (Al) having high strength but sufficiently deformable without breaking under stress is technically challenging in manufacturing to accelerate their applications to automotive and aerospace industries. Early studies demonstrated that significant microstructural refinement through severe permanent deformation by a combination of high-pressure and twisting (torsion) leads to excellent hardness in bulk metals. Thus, the objective of this project is to scientifically investigate how to achieve high strength and good elongations to failure in conventional Al alloys and intermetallic compounds after the microstructural refinement process. The importance of this project is to understand the strengthening and flow mechanisms of the nanostructured Al systems after the high-pressure and torsion processing, and to determine how to overcome the paradox of strength and formability in bulk nanostructured Al alloys and its compounds. These results are expected to have an important positive impact because a mechanistic understanding of improving the mechanical properties in bulk metals will provide new opportunities for the development of strategies for the applications of Al alloys and lightweight engineering materials selections. The research requires proficiency in a variety of areas including physics, materials science, and mechanical engineering, making it challenging and rewarding for graduate and undergraduate students who will be supported by this program.Technical Abstract: Achieving both high strength and good ductility is currently not controllable in Al alloys and intermetallic compounds. Although grain refinement by high-pressure torsion (HPT) generally improves the hardness of metals, the strategies for achieving both high strength and ductility in metallic materials are available only under limited conditions: in precipitation-hardened alloys or in materials containing high densities of nano-twins. Except in age-hardenable compositions, it is a major challenge to introduce those into Al systems having high stacking fault energy. Thus, objectives of this project are to understand the plastic flow mechanisms for strengthening and plasticity in micro- and macro-scales in ultrafine microstructures, and to design strategies to increase both strength and ductility of ultrafine-grained Al systems processed by HPT. This project combines expertise in metallurgical research on nanocrystalline materials with advanced characterization methods of measurements by the novel nanoindentation technique and state-of-the-art X-ray and electron diffraction analysis. These techniques allow to identify the complex metal flow with concurrent texture changes in a time scale under ambient and elevated temperatures. The contribution of this project is significant because the acquired scientific knowledge of improving mechanical properties of bulk metals can be extended to a wide range of polycrystalline materials, which is expected to expand our current engineering materials selections and produce an increased U.S. competitiveness in advanced manufacturing.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.