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

这项教师早期职业发展计划（Career）资助将通过一项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）及其合金微观结构演变的多尺度相互作用进行机制理解。在结构金属中，镁合金由于其重量轻（密度为铝的三分之二）、强度重量比大、成本相对较低、铸造性好，在减轻车辆重量方面表现出很大的希望，因此可以提高这些部件的燃油效率。尽管有这些优点，但镁合金在汽车工业中的全面采用受到延展性低和成形性差的限制，因此镁合金占汽车平均重量的比例不到1%。这些限制历来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和他们的团队将使用一种专门设计的多模态方法来理解在再结晶过程中与晶粒和变形结构相关的界面上的多尺度相互作用，这些相互作用控制着镁合金的晶体织构弱化。PI将建立几个项目和倡议，将科学研究成果与扩大代表性不足和边缘化群体参与材料科学和工程的目标相结合。CAREER拨款将支持一个研讨会的发展，该研讨会的重点是向传统黑人学院和大学（HBCU）的本科生介绍材料科学的概念和机会，设计和实施一个跨学科课程，旨在了解与材料相关的工程失败的人力成本，并实施一个项目，为俄亥俄州哥伦布市的小学生提供STEM资源。技术概述：本研究项目将关键性地推进对以下方面的理解：1)钙（Ca）和锌（Zn）的存在如何改变晶界附近的原子结构；2)与晶粒和变形孪晶相关的特定界面附近的位错相互作用如何控制再结晶过程中无应变晶粒的形核和生长；以及3)在这些再结晶晶粒生长过程中控制取向选择的最终机制。本研究的核心假设是，再结晶是由以下因素驱动的：1)在孪晶界附近和晶界附近形成局部高应变和不相容；2)在热处理过程中，Ca和Zn在晶界的优先共偏析导致界面边界迁移率的变化，促进了随机取向再结晶晶粒的形核和生长。再结晶与不同类型的边界或界面（即迁移率、能量）和错误取向的相关性为了解镁合金中主要的织构弱化机制提供了重要的见解。PI和团队将使用专门设计的多模态系统调查，采用高分辨率电子显微镜（透射、扫描）、高能x射线技术和原位实验相结合，以了解和揭示控制再结晶诱导织构弱化的机制。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.