Manipulating Nanoparticle-Modified Melt Pool Dynamics in Additive Manufacturing

金属增材制造（AM）是一种3D形状的逐层打印技术，是一种新兴的、具有潜在颠覆性的技术，它可以高效地制造出其他制造方法无法制造的复杂零件。然而，由于金属在打印过程中暴露在高温和反复熔化和凝固中，因此增材制造零件中气孔和裂纹等结构缺陷很常见，只有少数金属在该工艺中成功使用。本研究将研究在增材制造过程中向材料中添加纳米级陶瓷颗粒的好处。早期实验表明，纳米颗粒的存在有利于影响熔融金属的流动和微观结构的形成，消除裂纹，提高零件质量。然而，在许多情况下，这些实验结果的原因并没有得到很好的理解。通过对这些现象的预测理论和模型的发展，目前的工作旨在提供对纳米颗粒效应的科学理解，并为控制和优化增材制造零件质量提供新的策略。扩大增材制造的使用将提高美国制造业的竞争力，并通过实现高度可定制部件的快速生产，对美国工业产生重大影响。研究工作的主要技术目标是为金属增材制造中纳米颗粒修饰熔池的动力学建立物理理论和计算模拟。这项研究将通过三个相互关联的任务进行。首先，通过结合空间非均匀人口平衡方程（PBEs）和计算热流体动力学（CTFD），研究了含稀和致密纳米颗粒的液态金属的热物理行为。纳米颗粒对液态金属热物理性质的影响将被表征和验证。其次，通过建立纳米颗粒聚集和破碎过程的机理模型来预测纳米颗粒的迁移和聚集；该模型将根据凝固材料中颗粒分布的测量结果进行验证。最后，为了揭示纳米颗粒诱导晶粒细化和热裂还原的机制，将从先前推力区域获得的热和颗粒信息与详细的凝固模型相结合，其中元胞自动机（CA）晶粒生长模拟和晶间流动模型将预测裂纹敏感性。纳米颗粒的影响将包括通过一个基于物理的成核模型来阐明纳米颗粒影响的热裂力学。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。

Metal additive manufacturing (AM), the layer-by-layer printing of 3D shapes, is an emerging and potentially disruptive technology that allows the efficient fabrication of intricate parts that cannot be made using other manufacturing methods. However, because of the high temperature and repeated melting and solidification to which the metal is exposed as it is printed, structural flaws such as pores and cracks are common in AM parts, and only a small number of metals have been successfully used in the process. This research will study the benefits of adding nano-sized ceramic particles to the material during the AM process. Early experiments have shown that the presence of nanoparticles can favorably affect the flow of the molten metal and the formation of microscale structures, eliminating cracking and improving part quality. In many cases, however, the causes of these experimental results are not well understood. Through the development of predictive theory and models for these phenomena, the current work aims to provide scientific understanding of nanoparticle effects, and yield new strategies for controlling and optimizing AM part quality. Broadening the use of AM will advance the competitiveness of U.S. manufacturing and significantly impact U.S. industry by enabling the rapid production of highly customizable parts. The main technical objective of the researched work is to cultivate a physical theory and computational simulations for the dynamics of a nanoparticle-modified melt pool in metallic AM. The research will be undertaken through three interrelated tasks. First, thermophysical behavior of liquid metal with dilute and dense nanoparticles will be investigated by combining spatially inhomogeneous population balance equations (PBEs) and computational thermal fluid dynamics (CTFD). The effects of nanoparticles on thermophysical properties in liquid metal will be characterized and validated. Second, transport and aggregation of nanoparticles will be predicted by building a mechanistic model of aggregation and breakage processes; the model will be validated against measurements of particle distributions in solidified material. Finally, to unravel mechanisms of nanoparticle-induced grain refinement and hot cracking reduction, the thermal and particle information obtained from previous thrust areas will be coupled with a detailed solidification model, in which a cellular automaton (CA) grain growth simulation and an intergranular flow model will predict cracking susceptibility. Effects of nanoparticles will be included via a physics-based nucleation model to elucidate nanoparticle-affected hot cracking mechanics.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.