Effects of powder recycling, binder deposition, and HIP treatment on structure-property relationships in binder jetted 316 L stainless steel

This study investigates how powder condition (virgin vs. used), selective binder deposition (lattice and shell vs. bulk), and post-processing treatments (sintering vs. hot isostatic pressing - HIP) affect the microstructure, pore morphology, grain growth, and mechanical properties of binder-jetted 316 L SS parts. Parts printed with virgin powder achieved up to 3 % higher relative density in the green state compared to used powder. Bulk printing was evaluated alongside selective binder deposition strategies, with densification through sintering showing distinct influences of bound and unbound regions on pore fraction, size, and distribution. Parts printed with virgin powder attained relative densities exceeding 99.5 % after sintering, while the used powder showed up to 1 % lower relative sintered density. Consistent with the relative densities, both μ-CT and nonlinear ultrasonic-based sideband peak counting (SPC) method revealed the larger number and the sizes of pores present in the parts printed with used powder. Selective binder deposition was particularly effective in minimizing binder-powder interaction, thus, reducing porosity post-sintering. Grain size analysis revealed that sintered parts had an average grain size of 30–50 µm and pore sizes under 10 µm. Following HIP treatment, average grain size increased to 50–160 µm, with most pores eliminated. Microhardness rose slightly from 133 ± 10 HV_0.1 to 150 ± 13 HV_0.1 post-HIP, and tensile testing showed that virgin powder yielded parts with superior tensile strength and ductility. HIP treatment further enhanced elongation, though tensile strength slightly decreased. Microscopy and micro-computed tomography analysis indicated a ductile fracture mode.