Understanding and controlling low angle grain boundaries in additively manufactured metals

增材制造（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，在大多数AM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晶粒的晶体组成的。当颗粒彼此附着时，它们形成界面。这些界面通常可以控制材料的性能。理解和控制AM材料中的晶粒界面特别具有挑战性，这可能有助于我们获得更强，更可弯曲的材料。该项目通过综合的实验和计算工作，促进了对3D打印材料模型中加工、这些颗粒之间的界面以及由此产生的机械性能之间关系的理解。通过3D打印控制这些界面的能力可以为各种工程应用创建高性能结构材料。通过Samueli多样性计划参与代表性不足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。 本项目的目的是了解和控制AM金属和合金中的小角度晶界（LAGB）。该研究的重点是通过激光粉末床熔合（L-PBF）制造的纯金属，这些金属通常含有大量的LAGB，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、界面微观结构（例如，LAGB）和所得的机械性能。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LAGB的各种分数。使用透射电子显微镜（TEM）的逆极图取向映射是用来表征界面结构和相关的变形动力学参数和原位同步X射线衍射实验的特性。推力2致力于开发加工敏感模型，以将复杂的加工参数及其热历史与观察到的微观结构相关联。加工模型与微观结构表征紧密耦合，以揭示激光扫描策略和加工参数与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，以创建用于各种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劳动力的多样性。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.