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

这笔赠款支持研究，以填补有关充分利用三维打印来制造金属基复合材料和功能梯度材料的科学空白，这些材料既可以具有复杂的组成，也可以具有组成上的空间渐变。在这项工作中，金属合金由喷墨模块输送到粉末床上的纳米颗粒增强，并通过激光熔化。喷射纳米颗粒并用激光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和凝固后金属结构内的分散和重新分布的机制。研究成果用于在制造过程中控制或改变合金的成分，并减少金属基复合材料和分级结构的传统制造中涉及的步骤数量。由此产生的时间、成本和能源消耗的简化和减少推动了用于高温应用的创新材料设计的变革性变化，例如热交换器和燃烧室，这些设计促进了国民经济，推动了节能制造，并确保了国防安全。这项工作通过指导本科生和研究生，并通过校园暑期项目吸引有实践经验的高中生参与教育和外联工作，重点是增加和保留未被充分代表的少数群体在科学、技术、工程和数学方面的参与。当前粉末床熔合添加剂技术的技术和经济挑战，如选择性激光熔凝，防止在熔体中添加增强颗粒以生产金属基复合材料或不同的化学成分，以形成功能梯度合金。球磨作为一种生产混合粉末作为激光粉床工艺的原料的方法，给纳米粒子的分散和分布带来了挑战。球磨改变了粉末的形态，减少了流动、扩散、堆积和润湿行为，从而导致预制件中更高的孔隙率和裂纹。为了克服这一挑战，在粉末床中集成了喷射系统，以选择性和可控地将增强纳米颗粒添加到激光熔池中。通过耦合实验和对纳米颗粒注入熔池内的热和流体动力学现象的顺序降阶模拟，确定了纳米颗粒分布和再分布的机理。随着增强体含量的增加，熔池内较强的热毛细对流可以加速熔池内颗粒的重新排列。这一贡献意义重大，因为预计它将彻底改变选择性激光熔化作为一种原位成分变化和控制手段的使用，以实现有针对性的组织和性能，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。

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.