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

非技术性总结这项学院早期职业发展计划(Career)赠款将通过一项研究和教育计划促进国家科学进步，该计划使人们能够从机械上了解支配镁及其合金微结构演变的多尺度相互作用。在结构金属中，镁合金因其轻质(密度是铝的三分之二)、高强度重量比、相对较低的成本和良好的铸造性能而在车辆轻量化方面显示出巨大的前景，因此可以提高这些部件的燃油效率。尽管有这些优点，但镁合金在汽车行业的全面采用受到延展性和成形性差的限制，因此镁合金在汽车平均重量中所占比例不到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，但到目前为止，影响这一行为的机制仍不清楚。PI和他们的团队将使用专门设计的多模式方法来了解再结晶过程中与晶体颗粒和变形结构相关的界面上的多尺度相互作用，这些界面控制着镁合金的晶体织构弱化。国际和平研究所将建立几个项目和倡议，将科学研究成果与其目标相结合，扩大代表不足和边缘化群体在材料科学和工程领域的参与。这笔职业补助金将用于支持举办一个研讨会，重点是向历史悠久的黑人学院和大学(HBCU)的本科生介绍材料科学的概念和机会，设计和实施一门跨学科课程，旨在了解与材料相关的工程失败的人力成本，并实施一项向俄亥俄州哥伦布地区的小学生提供STEM资源的计划。技术总结这项研究计划将极大地促进人们对以下问题的理解：1)。钙(Ca)和锌(Zn)和2)的存在改变了晶界附近的原子结构。在再结晶过程中，与晶粒和形变孪晶相关的特定界面附近的位错交互作用控制着无应变晶粒的形核和长大。在这些再结晶颗粒的生长过程中，控制取向选择的最终机制。本工作的核心假设是再结晶是由以下因素驱动的：1)在孪晶界(Tb)和与晶界相关的晶界附近和晶界形成局域化的高应变和不相容；2)由于在热机械加工过程中Ca和Zn优先共偏析到晶界，导致界面迁移率的变化，促进了具有随机取向的再结晶晶粒的形核和长大。再结晶与不同类型的晶界或界面(即迁移率、能量)和取向偏差的关联为揭示镁合金中主要的织构弱化机制提供了重要的信息。PI和团队将使用专门设计的多模式系统调查，采用高分辨率电子显微镜(透射式、扫描式)、基于高能X射线的技术和现场实验相结合的方式，了解和揭示控制再结晶引起的织构减弱的机制。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.