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Binder jet 3D printing combined with post-deposition sintering is a non-beam additive manufacturing (AM) method for the creation of complex 3-dimensional structures. Binder saturation and particle morphology are two important factors affecting the quality of printed parts. Here, we investigated the effects of binder saturation on dimension accuracy, porosity, microstructure, and microhardness of nickel-based alloy 625 samples made of differently atomized powders. Argon gas atomized (GA) and water atomized (WA) nickel-based alloy 625 powders were used to binder jet samples for a detailed comparative study. The optimal binder saturation for WA system is 60 to 70%, whereas for GA system the optimal is about 80%. Generally, GA samples achieved better overall quality than WA samples in terms of packing density, dimensional accuracy, sintered density, and microhardness. This difference is attributed mainly to the particle morphology including sphericity and roundness. The critical threshold for visible binder bleeding phenomenon in WA and GA systems is determined to be 120% and 140% binder saturation, respectively. Mechanisms for binder bleeding phenomenon at different saturation levels for WA and GA systems are discussed in detail. A pore evolution model is proposed to better understand the printing and sintering processes. [ABSTRACT FROM AUTHOR]

The effects of post-build heat-treatments on the microstructure, phase formation, recrystallization behavior, and mechanical properties of laser powder bed additively manufactured Inconel 718 superalloy were investigated. Several heat-treatment schedules were used, including simulated hot isostatic pressing (HIP), and variations of the standard double aging treatment with various soaking times and quench procedures. Their effects on the precipitation, grain morphology, grain size, texture sharpness and mechanical properties were all documented. For the as-built coupons, columnar grains with inter-dendritic micro-segregation were formed along the build direction (xz-plane) with equiaxed grains forming on perpendicular sections to the build direction (xy-plane). After prolonged soaking times during the simulated HIP process, the microstructure transitioned from heterogeneous columnar grains to homogenous recrystallized grains with MC-type carbide precipitates. This leads to changes of microhardness (281 HV 2.0 to 171 HV 2.0), Young's modulus (209 GPa–229 GPa) and texture intensity. However, aging treatments increased both hardness and Young's modulus possibly because of formation of γ″ and γ′ precipitates in the Ni-matrix and the small effective grain size. Phase analysis using XRD confirmed the evolution of the precipitate formation. The combination of additive manufacturing and post-build heat-treatments can result in optimized microstructures and mechanical properties for specific applications depending on part requirements and operating conditions. [ABSTRACT FROM AUTHOR]