Nanoparticle Dispersion Mechanisms in Additively Manufactured Metal-matrix Composites and Functionally-graded Materials

这项拨款支持研究，以填补与充分利用三维打印制造金属基复合材料和功能梯度材料有关的科学空白，这些材料可以具有复杂的成分或成分的空间梯度。在这项工作中，通过喷墨模块将纳米颗粒输送到粉末床上，并通过激光束熔化金属合金。喷射纳米粒子和用激光束熔化的过程是逐层重复的，以创建三维金属基复合材料或功能梯度结构。本研究确定了三维打印过程中纳米颗粒在熔池内部以及凝固后在金属结构内部的分散和再分布机制。该研究成果可用于在构建过程中控制或改变合金的成分，并减少传统制造金属基复合材料和梯度结构所涉及的步骤。由此带来的时间、成本和能耗的简化和降低，推动了高温应用（如热交换器和燃烧室）创新材料设计的转型变革，从而促进了国民经济，推动了节能制造，并确保了国防安全。这项工作通过对本科生和研究生的指导，以及通过校园暑期项目吸引高中生的实践经验，促进教育和推广，重点是增加和保持未被充分代表的少数民族在科学、技术、工程和数学领域的参与。粉末床熔融添加剂技术目前面临的技术和经济挑战，如选择性激光熔化，阻碍了在构建过程中向熔体中添加增强颗粒，以生产金属基复合材料或改变化学成分以形成功能梯度合金。球磨作为一种生产粉末混合物作为激光粉末床工艺的原料的手段，对纳米颗粒的分散和分布提出了挑战。球磨改变了粉末的形态，减少了粉末的流动、扩散、堆积和润湿行为，从而导致成品部件的孔隙率提高和开裂。为了克服这一挑战，在粉末床中集成了一个喷射系统，可以选择性地、可控地向激光熔池中添加增强纳米颗粒。通过耦合实验和对纳米颗粒注入熔池内热流体力学现象的序贯降阶建模，确定了纳米颗粒分布和再分布的机制。随着增强物含量的增加，熔池内热毛细对流的增强可以加速熔池内颗粒的重新排列。这一贡献是重要的，因为它有望彻底改变选择性激光熔化的使用，作为原位成分变化和控制的手段，以实现目标的微观结构和性能，同时简化制造步骤，减少周期时间和成本。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。

This grant supports research to fill the scientific gap pertaining to full utilization of three-dimensional printing to make metal-matrix composites and functionally-graded materials that either can have a complex composition or spatial gradation in composition. In this work, a metallic alloy is reinforced by nanoparticles delivered by an ink-jet module to a powder bed and fused by a laser beam. The process of jetting nanoparticles and melting with a laser beam is repeated layer-by-layer to create a three-dimensional metal-matrix composite or functionally-graded structure. This research identifies the mechanisms of nanoparticle dispersion and re-distribution inside the melt pool and, after solidification, inside the metallic structure during three-dimensional printing. The research outcomes are used in controlling or varying the composition of the alloy during the build and reducing the number of steps involved in conventional manufacturing of metal-matrix composites and graded structures. The resulting simplification and reduction in time, cost and energy consumption drives transformational change for innovative material designs for high-temperature applications, such as, heat exchangers and combustion chambers, which promote the national economy, drive energy-efficient manufacturing, and secure the national defense. This work contributes to education and outreach through mentoring of undergraduate and graduate students, and engaging high school students with hands-on experience through campus summer programs with focus on increasing and retaining the participation of underrepresented minorities in science, technology, engineering, and math.Current technical and economic challenges in powder-bed fusion additive technologies, such as selective laser melting, prevent adding reinforcement particles to the melt during the build in order to produce metal-matrix composites or varying chemical composition to form functionally-graded alloys. Ball-milling as a means to produce the powder mixture as feedstock for laser powder-bed processes presents nanoparticle dispersion and distribution challenges. Ball-milling changes the morphology of the powder and reduces flow, spreading, packing and wetting behavior leading to higher porosity and cracking in the as-built components. To overcome this challenge, a jetting system is integrated into the powder-bed to selectively and controllably add reinforcement nanoparticles to the laser melt pool. Mechanisms for nanoparticle distribution and redistribution are determined through coupled experiment and sequential reduced-order modeling of the thermal and hydrodynamic phenomena within the nanoparticle-injected melt pool. With increasing reinforcement content, stronger thermo-capillary convection within the melt pool can accelerate the re-arrangement of particles inside the melt pool. This contribution is significant because it is expected to revolutionize the use of selective laser melting as a means of in-situ composition variation and control to achieve targeted microstructures and properties while simplifying manufacturing steps and reducing cycle time and cost.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.