Influence of infill architecture on shrinkage, microstructure, and mechanical properties in paste extrusion 3D printed stainless steel

Abstract

Metal Paste Deposition is an emerging additive manufacturing method that extrudes metal paste to form green parts, which are subsequently sintered for densification. This study investigates the influence of infill pattern on the macro- and microstructural properties of sintered 316 L stainless steel parts. Comprehensive experimental characterization, including porosity analysis, grain size measurement, phase identification, 3D scanning, and nanohardness testing, was conducted across multiple surfaces and regions. Results revealed that porosity and elastic modulus varied with both infill geometry and local position. Grain size remained consistent across all patterns and locations, averaging ∼50 µm. Nanoindentation measurements revealed that hardness values remained within the expected range for 316 L stainless steel (2.6–4.5 GPa), showing minimal variation across different regions. Pores were predominantly circular, with circularity values ranging from 0.96 to 0.99, suggesting effective surface-energy-driven densification. Among all tested patterns, the “grid” infill pattern achieved the highest densification and stiffness due to increased bead overlap. A bead-level finite element simulation, using reconstructed geometries from G-code, captured localized shrinkage, porosity evolution, and grain growth trends, showing good agreement with experiments. These results validate the simulation framework and highlight the importance of infill design in optimizing part performance and reliability. All findings reported here are specific to parts fabricated at 50% nominal infill density and processed under the studied sintering conditions (12 h cycle with 4 h hold at 1380°C).