Understanding and controlling low angle grain boundaries in additively manufactured metals

【非技术】增材制造（AM）或3D打印具有将材料合成和制造集成到单个打印中的能力，对于广泛的技术应用具有吸引力，并可能有助于迎来工业4.0革命。然而，对大多数增材制造材料的加工-结构-性能关系的基本理解仍然缺乏。几乎所有的增材制造材料都是由许多称为颗粒的晶体组成的。颗粒相互连接时形成界面。这些界面通常可以控制材料的性质。理解和控制增材制造材料中的晶粒界面尤其具有挑战性，这可能有助于我们获得更强、更可弯曲的材料。该项目通过综合实验和计算工作，促进了对模型3d打印材料中加工，这些颗粒之间界面和由此产生的机械性能之间关系的理解。通过3D打印控制这些接口的能力可以为各种工程应用创造高性能结构材料。通过Samueli多样性计划和与国家实验室的合作，参与代表性不足的本科生研究，为先进制造和材料科学领域的年轻科学家提供教育和职业发展机会。本项目的目的是了解和控制增材制造金属和合金中的低角晶界（LAGBs）。研究的重点是激光粉末床熔合（L-PBF）制备的纯金属，这种材料通常含有大量的lagb，可以实现高强度、高延展性和高热稳定性。该项目旨在建立对激光加工参数、界面微观结构（例如lagb）和由此产生的机械性能之间相互联系的机理理解。该研究包括两个主要的推力：推力1涉及控制制造模型材料与不同分数的lagb。利用透射电子显微镜（TEM）对界面结构进行了表征，并将其特征与变形动力学参数和原位同步加速器x射线衍射实验相关联。Thrust 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。加工模型与微观结构表征紧密耦合，揭示了激光扫描策略、加工参数和所得微观结构之间的基本关系。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，以创建各种应用的高性能结构材料。与国家实验室的合作提高了研究生的研究经验。与Samueli多元化项目合作，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劳动力的多样性。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-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.