CAREER: Understanding the origins of pearlite discontinuities in eutectoid microstructures: Modeling & Experiments

第1部分：非技术概述有许多不同类型的钢和几种方法来分类它们。将它们分组的一种方法是根据在显微镜下仔细观察它们时看到的结构类型。研究金属的科学家将这些只有在极高放大倍数下才能看到的结构称为“微观结构”。“珠光体”或“珠光体微观结构”是一种具有层状微观结构的钢，其坚硬且坚固，并且通常用于需要高强度的应用中，例如铁路、吊桥支撑缆索和切割工具。然而，在许多其他应用中，钢需要软化，然后才能成形或加工成复杂的形状。虽然钢已经被使用和研究了很多代，但理解不同的加工条件如何具体影响钢的微观结构有些有限，特别是在商业钢中，复杂的化学成分使得难以理解原子水平上发生的事情。这个CAREER奖，它集成了计算，实验和表征技术，将允许一个有组织的研究检查珠光体钢的层状微观结构和产生它们的原子相互作用的断裂。具体来说，这项研究将使用仅含有四种元素中的三种（铁，碳和锰或硅）的模型钢的加热和冷却实验，结合计算机模拟和先进的2D，3D和4D（3D通过时间）成像，以研究材料的制造方式与它们所拥有的微观结构之间的关系。建立这些关系将使微观结构水平的控制，在钢铁部件的制造，这是目前在炼钢知识的缺失位。该项目的外展部分解决了弥合材料研究与材料科学与工程（MSE）国家年度招生短缺之间巨大差距的迫切需要。为了实现这一目标，该项目鼓励各级学生通过以学生为中心的交流，结合主动学习，在MSE领域追求教育和职业。这种方法，它可以帮助解决许多社区的具体需求，代表性不足的人口将被纳入一个量身定制的外展计划，高中，本科生和研究生。第2部分：技术总结钢的显微组织组成的层状珠光体被称为具有高的抗拉强度，优良的韧性，和硬度，由于其分层的显微组织。然而，为了增强这种微结构的可成形性，钢必须软化，这通常通过退火热处理来实现，该退火热处理促进珠光体的球化或非协同演变。添加合金元素，如锰和硅也可以影响珠光体球化，导致层状不连续性和改善的延展性。遗憾的是，目前对珠光体不连续性产生的机制以及它们如何受到合金成分、加工温度、原奥氏体晶粒尺寸和位错密度的影响的理解还有很多需要改进的地方。虽然理解加工过程中的多组分扩散和珠光体显微组织演变具有挑战性，但对最终决定机械性能的显微组织施加更大的控制是必要的步骤。由于相形态的演变不能通过实验或孤立的数值计算来预测，因此需要开发一种综合方法，将相场模型与实验，表征和微观结构量化相结合，以更好地理解加工-微观结构关系。为了整合和利用现有的高保真工具，该CAREER奖测试了钢显微组织中珠光体片层的不连续生长是通过非合作机制发生的假设。 为了检验这一假设，三元Fe-C-Mn和Fe-C-Si钢的计算和退火研究将通过先进的表征技术进行补充，例如X射线计算机断层扫描，利用能量色散光谱的分析透射电子显微镜和电子背散射衍射。虽然使用空间相关函数的模拟和表征的微观结构的比较将有助于基本理解的机制，诱导片状珠光体微观结构的不连续性，加工微观结构的联系将推导出通过所获得的数据集的主成分分析。该项目的更广泛影响存在于两个部分。第一个是开发和免费传播一个综合的实验，计算和四维表征协议的层状不连续性钢。第二个项目利用本项目的技术研究，通过四个活动部分实现的主动学习，部署以学生为中心的教育和推广计划：（i）本科和高中“偶像”计划，（ii）本科研究，（iii）本科和研究生课程开发，及（iv）遥控相─该奖项反映了NSF的法定使命，并被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准。

PART 1: NON-TECHNICAL SUMMARY There are many different types of steels and several ways to categorize them. One way to group them is according to the types of structures one sees when looking closely at them under a microscope. Scientists who study metals call these structures that are only visible at extremely high magnification, "microstructures". "Pearlite" or "Pearlitic microstructures" are a type of steel that has a layered microstructure that is hard and strong and is commonly used in applications that require high strength such as railroads, drawbridge support cables, and cutting tools. However, in many other applications, steel needs to be softened before they can be formed or machined into complex shapes. Although steels have been used and studied for many generations, understanding how different processing conditions specifically impact steel microstructure is somewhat limited, particularly in commercial steels where complex chemical compositions make understanding what is occurring on an atomic level difficult. This CAREER award, which integrates computational, experimental, and characterization techniques, will allow for an organized study examining breaks in the layered microstructures of Pearlitic steels and the atomic interactions that produce them. Specifically, this study will use heating and cooling experiments on model steels containing only three of four elements (Fe, Carbon and Manganese or Silicon) in conjunction with computer simulations and advanced 2D, 3D and 4D (3D through time) imaging to investigate the relationship between how materials are made and what microstructures they come to possess. Establishing these relationships will enable microstructure level control in the manufacturing of steel components, which is currently a missing bit of knowledge in steel-making. The outreach component of this project addresses the pressing need to bridge the vast gap between materials research and national annual enrollment shortages in Materials Science and Engineering (MSE). In pursuit of this goal, this project encourages students at all levels to pursue education and careers in MSE fields through student-centric communication that incorporates active learning. This approach, which can help address many community-specific needs for underrepresented populations will be incorporated into a tailored outreach plan for high-school, undergraduate and graduate students.PART 2: TECHNICAL SUMMARYSteel microstructures consisting of lamellar pearlite are known to possess high tensile strength, excellent toughness, and hardness due to their layered microstructure. However, to enhance the formability of such microstructures, steel must be softened, which is typically accomplished via annealing heat treatments that facilitate the spheroidization or non-cooperative evolution of pearlite. The addition of alloying elements, such as Manganese and Silicon can also impact pearlite spheroidization, leading to lamellar discontinuities and improved ductility. Unfortunately, current understanding of the mechanisms by which pearlitic discontinuities arise and how they are influenced by alloy composition, processing temperature, prior austenite grain size, and dislocation densities leave much to be desired. While comprehending multi-component diffusion and pearlitic microstructural evolution during processing is challenging, it is a necessary step to exert greater control on microstructure which ultimately determines mechanical properties. Since the evolution of phase morphologies cannot be predicted through experiments or numerical calculations in isolation, the development of an integrated approach, that combines phase-field models with experiments, characterization, and microstructure quantification is required to better understand processing-microstructure relations. To integrate and leverage existing hi-fidelity tools, this CAREER award tests the hypothesis that discontinuous growth of pearlitic lamellae in steel microstructures occur by a non-cooperative mechanism. To examine this hypothesis, computational and annealing studies of ternary Fe-C-Mn and Fe-C-Si steels will be complemented by advanced characterization techniques such as X-ray Computed Tomography, Analytical Transmission Electron Microscopy leveraging Energy Dispersive Spectroscopy, and Electron Backscatter Diffraction. While a comparison of simulated and characterized microstructures using spatial correlation functions will facilitate a basic understanding of the mechanisms that induce lamellar discontinuities in pearlitic microstructures, processing-microstructure linkages will be deduced through Principal Component Analyses of the obtained datasets. The broader impacts of this project exist in two parts. The first is the development and free dissemination of an integrated experimental, computational and four-dimensional characterization protocol for lamellar discontinuities in steels. The second leverages the technical research of this project to deploy student-centric education and outreach programs using active learning realized in four segments of activity: (i) undergraduate and high-school “Idol” programs, (ii) undergraduate research, (iii) undergraduate and graduate course development, and (iv) remote phase-field workshops.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.