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

Arizona State University, Scottsdale AZ

Investigators

Abstract

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.