CAREER: Understanding Interface Controlled Mechanisms of Recrystallization in Microstructurally Complex Mg Alloys

非技术总结本学院早期职业发展计划（CAREER）拨款将通过研究和教育计划促进国家科学进步，该计划使人们能够对镁（Mg）及其合金中微观结构演变的多尺度相互作用进行机械理解。在结构金属中，镁合金由于其重量轻（密度为铝的三分之二）、大的强度重量比、相对低的成本和良好的可铸造性而在减轻车辆重量方面显示出很大的前景，并且因此可以提高这些部件的燃料效率。尽管有这些优点，但镁合金在汽车工业中的全面采用受到低延展性和差成形性的限制，因此镁占平均车辆重量的不到1%。这些限制在历史上与热机械加工过程中形成的微观结构有关，但迄今为止，影响这种行为的机制仍然未知。PI及其团队将使用专门设计的多模态方法来了解与晶粒和再结晶过程中变形结构相关的界面处的多尺度相互作用，这些相互作用控制着镁合金中的晶体织构弱化。PI将建立几个计划和倡议，将科学研究成果与扩大材料科学和工程中代表性不足和边缘化群体的参与目标相结合。职业赠款将支持一个研讨会的发展，重点是向历史上黑人学院和大学（HBCU）的本科生介绍材料科学的概念和机会，设计和实施旨在了解材料相关工程失败的人力成本的跨学科课程，并实施一项计划，为哥伦布，OH地区的小学生提供STEM资源。技术总结本研究计划将严格推进如何理解：1）。晶界附近的原子结构由于钙（Ca）和锌（Zn）的存在而改变，以及2）。与晶粒和形变孪晶相关的特定界面附近的位错相互作用控制再结晶期间无应变晶粒的形核和生长以及3）。在这些再结晶晶粒的生长过程中控制取向选择的产生机制。这项工作的核心假设是再结晶是由以下因素驱动的：1）在孪晶晶界（TB）和与晶粒相关的晶界附近和横跨它们的局部高应变和不相容性的形成，以及2）由于优先共晶，在热机械加工过程中，Ca和Zn向晶界的偏析促进了再结晶晶粒的形核和生长，方向。再结晶与不同类型的边界或界面（即，流动性，能量）和取向差提供了重要的洞察镁合金中的主要织构弱化机制。PI和团队将使用专门设计的多模式系统调查，该调查采用高分辨率电子显微镜（透射、扫描）、基于高能X射线的技术，而在─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 SUMMARYThis Faculty Early Career Development Program (CAREER) grant will promote national scientific advancement through a research and education program that enables the mechanistic understanding of the multi-scale interactions that govern microstructural evolution in magnesium (Mg) and its alloys. Of the structural metals, Mg alloys, show great promise in vehicle weight reduction due to their lightness (two-thirds the density of aluminum), great strength-to-weight ratio, relatively low cost, and good castability and as a result can improve fuel efficiency in these components. Despite these advantages, the full adoption of Mg alloys in the automotive industry is limited by low ductility and poor formability and as a result Mg accounts for less than 1 percent of the average vehicle weight. These limitations have been historically linked to the microstructure that develops during thermomechanical processing but to date the mechanisms that influence this behavior are still unknown. The PI and their team will use a specifically designed, multi-modal methodology to understand the multi-scale interactions at interfaces associated with crystalline grains and deformation structures during recrystallization that govern crystallographic texture weakening in Mg alloys. The PI will establish several programs and initiatives that integrate the scientific research outcomes with their goal of broadening participation of under-represented and marginalized groups in materials science and engineering. The CAREER grant will support the development of a workshop focused on introducing concepts and opportunities in materials science to undergraduate students at historically black college and universities (HBCU), design and implement a cross-discipline course aimed at understanding the human cost of material-related engineering failures and implement a program providing resources in STEM to elementary school students within the Columbus, OH area. TECHNICAL SUMMARYThis research program will critically advance the understanding of how the: 1). atomic structure near grain boundaries is altered by the presence of calcium (Ca) and zinc (Zn) and 2). dislocation interactions near specific interfaces associated with grains and deformation twins govern the nucleation and growth of strain-free grains during recrystallization as well as the 3). resulting mechanisms that govern orientation selection during growth of these recrystallized grains. The core hypothesis of this work is that recrystallization is driven by: 1) the formation of localized high strains and incompatibilities near and across twin boundaries (TB) and boundaries associated with crystalline grains and 2) changes in interface boundary mobility due to the preferential co-segregation of Ca and Zn to grain boundaries during thermomechanical processing promotes the nucleation and growth of recrystallized grains with randomized orientations. Correlation of recrystallization with boundaries or interfaces of varying type (i.e., mobility, energy) and misorientation provides important insight into the dominant texture weakening mechanisms in Mg alloys. The PI and team will use a specifically designed, multi-modal systematic investigation that employs a combination of high-resolution electron microscopy (transmission, scanning), high energy X-ray based techniques, and in-situ experimentation to understand and uncover the mechanisms that control recrystallization induced texture weakening.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.