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Binder jetting is a powder bed additive manufacturing process where an object is created by depositing liquid binder onto the surface of powder, selectively binding particles in each layer. The quality of the as-printed parts is influenced not only by process parameters such as layer thickness, binder saturation, print speed, and drying time but also by the location within the build box. This study highlights the location-dependent nature of green density and dimensional accuracy in the as-printed samples, and the observed trends are thoroughly discussed. A conventional powder spreading using a single roller was compared with a double roller to maximize powder packing and bed uniformity prior to binder jetting process. The significance of these observations lies in their impact on densification behavior, shrinkage, and the final geometry of the printed part. 

In binder jetting, shrinkage and deformation occur during the sintering step, both of which are affected by the green density of the binder jetted materials. The study innovatively introduces a cost-effective, practical, and in-process monitoring system for visualizing shrinkage and deformation on larger samples than conventionally observed using small-scale specimens in dillatometry equipment. The powder characteristics and binder jet printing process itself influence the initial green density. The comprehensive analysis of powder flowability and packing density, densification behavior, and shrinkage reveals that the consolidated parts using virgin powder (with a green density of 55%) can achieve a relative density above 99.9% with an anisotropic shrinkage in the Z>X>Y direction. In contrast, the used or recycled powder exhibits a lower green density of ∼48%, higher shrinkage rate in all three dimensions, and a decreased degree of anisotropy. Using in-process imaging and experimental data on the grain size attained through optical microscopy and electron backscatered diffraction imaging, the material's shear and bulk viscosities were determined. The formation of delta-ferrite and its impact on densification were discussed in the context of solid-state and supersolidus liquid phase sintering. The model relied on the continuum sintering theory formulated by Skorohod and Olevsky. The strain evolution from the in-situ imaging of sintering process is correlated with porosity based on the used feedstock and applied sintering temperatures. The outcomes of this study offer valuable perspectives on anisotropic sintering mechanisms, bridging the knowledge gap regarding the relationships between structures produced through binder jetting and subsequent sintering of materials. 

Study examines binder deposition methods (bulk vs. selective printing) and sintering atmospheres (vacuum vs. H2) on binder jetted 316 L stainless steel components. The density of the H2-sintered specimens was found to be lower (up to 5%) compared to the vacuum-sintered parts with the final density of 99.7%. Grain size analysis indicated smaller grains in the H2-sintered parts (∼26 μm) compared to vacuum-sintered condition (∼33 μm) in the bound area which could be attributed to the presence of residual pores that impeded grain growth. The H2-sintered specimens exhibited an elongation of 25% and an ultimate tensile strength (UTS) of 460 MPa, whereas the vacuum-sintered parts displayed an elongation of 70% and a UTS of 550 MPa. Fractography analysis using microscopy and micro-computed tomography revealed ductile fracture in the vacuum-sintered samples, while the H2-sintered parts exhibited a combination of brittle and ductile fracture due to remnant pores in the microstructure.