Understanding and controlling low angle grain boundaries in additively manufactured metals

非TECHANICAL摘要添加制造(AM)，或3D打印，具有将材料合成和制造集成到单一打印中的能力，对广泛的技术应用具有吸引力，并可能有助于迎来行业4.0革命。然而，对大多数AM材料中的加工-结构-性能关系仍然缺乏基本的了解。几乎所有的AM材料都是由许多称为颗粒的晶体组成的。当颗粒相互连接时，就会形成界面。这些界面通常可以控制材料属性。理解和控制AM材料中的颗粒界面尤其具有挑战性，这可能有助于我们获得更坚固和更具弯曲性能的材料。该项目通过集成的实验和计算工作，促进了对3D打印材料模型中的加工、这些颗粒之间的界面和所产生的机械性能之间的关系的理解。通过3D打印控制这些界面的能力可以为各种工程应用创造高性能的结构材料。通过Samueli多样性计划参与的未被充分代表的本科生研究，以及与国家实验室的合作，为先进制造和材料科学领域的年轻科学家提供了教育和职业发展机会。本项目的目标是了解和控制AM金属和合金中的小角度晶界(LAGB)。研究的重点是激光粉床熔化制备的纯金属(L-PBF)，这种纯金属通常含有大量的LAGBs，可以导致高强度、高延展性和高热稳定性。该项目旨在建立对激光加工参数、界面微结构(例如LAGB)和由此产生的机械性能之间的相互联系的机械理解。这项研究包括两个主要推进器：推进器1涉及控制制造含有不同分数的LAGBs的模型材料。利用透射电子显微镜(TEM)的逆极图取向图表征了界面结构，并将其特征与变形动力学参数和原位同步辐射X射线衍射实验进行了关联。推进器2致力于开发加工敏感模型，将复杂的加工参数及其热历史与观察到的微观结构联系起来。该工艺模型与显微组织表征紧密耦合，揭示了激光扫描策略与工艺参数和所得到的显微组织之间的基本关系。通过这些研究获得的机理见解可以指导激光加工条件的优化，以创造出适用于不同应用的高性能结构材料。与国家实验室的合作增强了研究生的研究经验。与Samueli多样性计划合作，让来自代表性不足群体的本科生参与这些研究活动，增加了未来STEM工作队伍的多样性。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-TECHANICAL ABSTRACTAdditive manufacturing (AM), or 3D printing, with its ability to integrate materials synthesis and manufacturing into a single print, is attractive for a broad range of technological applications and may help usher industry 4.0 revolution. However, a fundamental understanding of the processing-structure-property relationship in most AM materials remains lacking. Nearly all AM materials are made of numerous crystals called grains. Grains form interfaces when attached to each other. These interfaces can often control materials properties. It has been particularly challenging to understand and control grain interfaces in AM materials, which may help us to achieve stronger and more bendable materials. This project advances understanding of the relationship between processing, interfaces between these grains, and resultant mechanical properties in a model 3D-printed material through an integrated experimental and computational effort. The ability to control these interfaces via 3D printing could allow the creation for high-performance structural materials for various engineering applications. The involvement of under-represented undergraduate research through Samueli Diversity Program and collaborations with national laboratories provide educational and career advancement opportunities for young scientists in advanced manufacturing and materials science fields. TECHANICAL ABSTRACTThe objective of this project is to understand and control low angle grain boundaries (LAGBs) in AM metals and alloys. The research focuses on pure metals fabricated by laser powder-bed-fusion (L-PBF), which often contain a substantial fraction of LAGBs that can lead to high strength, high ductility, and high thermal stability. The project aims at establishing mechanistic understanding of interconnections between laser processing parameters, interfacial microstructures (e.g., LAGBs), and resultant mechanical properties. The research comprises of two major thrusts: Thrust 1 involves controlled fabrication of model materials with various fractions of LAGBs. An inverse pole figure orientation mapping using transmission electron microscopy (TEM) is used to characterize interfacial structures and correlate their characteristics to the deformation kinetics parameters and in situ synchrotron x-ray diffraction experiments. Thrust 2 strives to develop processing sensitive models to correlate complex processing parameters and its thermal history with the observed microstructures. The processing model is tightly coupled with microstructure characterizations to reveal the fundamental relationship between the laser scan strategies and processing parameters and resultant microstructures. The mechanistic insights obtained by these studies could guide the optimization of laser processing conditions to create high performance structural materials for diverse applications. Collaborations with national laboratories enhance the graduate student’s research experience. Partnership with the Samueli Diversity Program to engage undergraduate students from under-represented groups into these research activities increases the diversity of the future STEM workforce.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.