Low-Temperature Laser-Sinterable Nanostructured Feedstock to Improve the Speed of Metal 3D Printing, and to Enable Polymer-Metal Concomitant Printing

金属添加剂制造(AM)技术依赖于粉末原料的高能激光烧结，以制造航空航天、国防和医疗行业的高强度、复杂形状的金属部件。启用激光的AM需要大量能量来产生足够高的温度(500-1500摄氏度)来烧结原料，因此这一过程非常缓慢，有时需要数天来打印0.3立方米的材料。最近对金属纳米材料的研究表明，它们具有独特的性能，包括降低烧结温度(200-750摄氏度)，以及在纳米尺度上增强激光与物质相互作用产生的热。在本项目中，将研究激光与一类新型AM相容的纳米结构金属粉末原料的相互作用。将注意定制新的原料，以减少烧结所需的热能和加工时间。如果成功，这种方法可以在添加金属工艺中消除对高能激光光源的需求，降低资本和运营成本，提高安全性并扩大其工业应用。此外，实现低温可烧结金属原料是通过添加工艺产生可行的聚合物-金属界面的一步；目前这是一个挑战，因为聚合物可以在当前的金属烧结温度(500℃)下进行热降解。金属-聚合物共处理将允许学者和医疗行业打印仿生膝关节植入物，不仅模仿人类的硬组织(例如骨骼)，而且还模仿软组织(例如韧带)。除了技术方面，该项目还支持夏季研究生实习和高中添加剂制造竞赛；这两项活动都旨在吸引和培训未来美国劳动力所需的下一代制造工程师和科学家。可以通过去合金方法生产纳米多孔金属粉末，例如韧带尺寸小于50纳米的金属粉末。由于它们的表面形貌与气体雾化产生的固体颗粒不同，它们与入射激光的相互作用也不同。本项目旨在了解纳米多孔金属粉末的合成和激光烧结。对介孔金属粉末合成的研究将决定通过化学脱合金化来控制气孔形成和控制的物理和局限性。这些新颗粒与激光光源的相互作用将被研究，以阐明在烧结过程中，气孔韧带内的局域表面等离子体共振如何促进轻物质相互作用，以及依赖于尺寸的熔点抑制如何降低加工所需的激光能量密度和停留时间。研究任务包括：1)研究金属合金脱合金化的过程-结构图，以量化吸附原子聚集在成孔理论中的作用；2)实验工作，以了解介孔金属连接的标度规律；3)表征激光照射下微结构形态演变的阶段，如孔粗化；以及4)3D打印试件的力学表征，以阐明低温焊接金属-金属和金属-聚合物部件界面强度的基本极限。如果成功，这些基本知识可以被用来提高金属AM的速度，并增加其与热塑性塑料的可梳合性，以同时打印聚合物和金属。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。

Metal additive manufacturing (AM) technologies rely on high-energy laser sintering of powder feedstock to fabricate high-strength, complex shaped, metal components for the aerospace, defense and medical industries. Laser enabled AM requires large amounts of energy to generate sufficiently high temperatures (500-1500 C) to sinter the feedstock, thus making it a notably slow process sometimes needing days to print 0.3 cubic meters of material. Recent studies on metal nanomaterials revealed they have unique properties that include reduced sintering temperatures (200-750 C), and enhanced heat generation resulting from laser light-matter interaction at the nano-scale. In this project, the laser interaction with a new class of AM-compatible nanostructured metal powder feedstock will be investigated. Attention will be given to tailoring the new feedstock so as to reduce the thermal energy and processing time requirements for sintering. If successful, this approach could eliminate the need for high-energy laser sources in additive metal processes, bringing capital and operational costs down, improving safety and expanding its industrial application. Further, realizing low-temperature sinterable metal feedstock is a step towards generating viable polymer-metal interfaces via additive processes; currently this is challenging as the polymer can undergo thermal degradation at current metal sintering temperatures (500 C). Metal-polymer co-processing would allow academics and the medical industry to print bio-inspired knee-implants mimicking not only human hard tissues (e.g. bone) but also soft ones (e.g. ligaments). In addition to the technical aspects, this project supports a summer graduate student traineeship, and a high-school competition in additive manufacturing; both activities aim to attract and train the next-generation of manufacturing engineers and scientists required for future US workforce needs.Nanoporous metal powders, e.g. with ligament size smaller than 50 nm, can be generated via dealloying methods. As their surface topography differs from solid particles generated via gas atomization they interact differently with incident laser beams. This project seeks to understand both the synthesis and laser sintering of nanoporous metal powder. Research focused on the synthesis of mesoporous metal powders will determine the physics and limitations of pore formation and control via chemical dealloying. The interaction of these novel particles with the laser source will be studied to elucidate how localized surface plasmon resonance within the ligaments of the pores can promote light-matter interaction during the sintering process, and how size-dependent melt-point suppression reduces the laser energy density and dwell requirements for processing. Research tasks include: 1) an investigation of the process-structure mapping of dealloying of metal alloys to quantify the role of adatom clustering in the pore formation theory, 2) experimental work to understand the scaling laws of mesoporous metal joining, 3) characterization of the stages of microstructural morphology evolution upon laser exposure such as pore coarsening, and 4) mechanical characterization of 3D printed specimens to elucidate the fundamental limit on the interfacial strength of low-temperature welded metal-metal and metal-polymer parts. If successful, this fundamental knowledge can be leveraged to improve the speed of metal AM and increase its combability with thermoplastics for simultaneous printing of polymers and metals.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.