Anisotropic sintering shrinkage behavior of stainless steel fabricated by extrusion-based metal additive manufacturing

Metal additive manufacturing (AM) can be achieved by first extruding polymer-based filaments with densely filled metal particles to create the so-called ‘green’ parts and then experiencing debinding and sintering to produce finished metal components. As a critical step, sintering governs the shape dimension, relative density, and resultant strength of final parts. Thus, there is a growing need for research on understanding and quantifying the sintering-induced anisotropic shrinkage. In this work, the underlying behaviors of anisotropic shrinkage during the entire sintering of extrusion-printed stainless steel 316L parts will be understood and quantified through a combination of theoretical study and experimental investigations including three-directional dilatometry, scanning electron microscopy, and X-ray computed tomography. The three-dimensional size evolution of ‘brown’ parts before sintering will be studied through a macroscopic analysis of shrinkage anisotropy factors and microstructure characterizations. Different filling strategies will be integrated with initial pore distribution characterization for anisotropic dimensional change analysis. The heterogeneous pore distribution will be discussed in conjunction with the anisotropic viscous behavior to eventually unveil the shrinkage performance in the course of sintering. The findings of this work will provide insights into the anisotropic sintering mechanisms and fill the knowledge gap of the relations between extrusion-based metal AM process and sintered structures of metal alloys.