Mechanistic Understanding of Multi-scale Sintering Behavior Influenced by Anisotropic Particle and Pore Distributions in Extrusion-based Metal Additive Manufacturing

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Without melting materials, metal additive manufacturing can also be achieved by first extruding filaments (in a 3D printing fashion) that contain densely filled metallic particles and polymetric binders, to form the so-called green parts, and then undergoing debinding and sintering to produce finished metal components. This relatively new metal additive manufacturing process nonetheless has technical challenges too including element segregations occurred in sintering and printing-induced anisotropic particle distributions that complicate the prediction of resultant micro- and macro-structures. This award supports fundamental research to understand the multi-scale underlying mechanisms occurred in sintering 3D filament-printed stainless steel parts using a combination of multi-physics simulations, analytical modeling, and experimental characterization and testing. The approach of extrusion-printing, debinding and sintering features ease of part handling and reduction of production costs, especially for large-sized metal component fabrications. The knowhow of this metal additive manufacturing technology will heighten manufacturing competitiveness in key industries such as aerospace, energy, automotive, and defense. The project will promote the participation of underrepresented groups such as African American and female students through summer research immersion programs. The research findings will be spread to local K-12 students through onsite interactive demonstrations and virtual micro-learning videos, also to the industry and community through an additive manufacturing symposium at Binghamton University.The overall goal of this research is to establish a fundamental understanding of the mechanisms that govern anisotropic sintering behaviors at atomistic, microscopic, and macroscopic scales during extrusion-printing, debinding and sintering of stainless steel parts. The interactions between atomic diffusion and multi-element redistribution will first be discovered by molecular dynamics simulations to examine the dominant mechanism that affects the grain boundary migration at the atomic scale. The team will then uncover the microscale pore distribution and grain evolution with sintering temperatures and times using approaches like discrete element method, in which temperature-dependent diffusion parameters determined from molecular dynamics will be incorporated to derive particle contact evolution and grain growths during sintering. A constitutive model will be developed to calculate the macro-scale anisotropic shrinkage and distortions during sintering. The prediction of element segregation, grain-boundary defects, pore distribution, grain size, and anisotropic deformation of sintered specimens will be experimentally validated by material characterizations, including x-ray computed tomography, complemented by measuring the resultant mechanical properties of sintered specimens. The project will also establish a semi-empirical process-structure-property relationship to guide the fabrication of stainless steel parts with desired properties. This findings are expected to advance the design, fabrication, and application of alloys with predictable microstructures and macroscopic characteristics as well as tailorable mechanical performance.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.