Mechanical anisotropy and fracture mode of binder jetting 3D printed calcium sulfate moldings

Abstract Binder jet three-dimensional (3D) printing has been extensively developed since the early 1990s and is widely applied in various industrial fields. Binder jetting 3D-printed products have anisotropic mechanical properties; however, no study has provided a systematic explanation of this mechanism. Herein, we propose that the crystal lattice model based on the crystallographic logic can explain the mechanical anisotropy and fracture mode of 3D-printed products based on the nozzle pattern (resolution) of the print head. In this study, calcium sulfate-base powder was hardened by ejecting different amounts of water-base ink, and the crystal phases, mechanical anisotropy, and fracture mode of the cylindrical moldings printed in the x-, y-, and z-directions and in the directions rotated from these axes with a binder jetting 3D printer were investigated. The results revealed that the content of calcium sulfate hemihydrate/dihydrate and the density of the moldings printed in each direction were almost constant, regardless of the ink/volume ratio; however, the content of the formed hemihydrate and amorphous anhydrate calcium sulfate was dependent on the ratio to a certain extent. The mechanical anisotropy and the different fracture modes (crack propagation) of the moldings printed in different directions at a constant lamination thickness were reproducibly observed. The authors found that the direction of the crack propagation represented by a Miller index was affected by the nozzle pattern of the print head. This study provides new insights to comprehensively explain anisotropic mechanical properties of binder jetting 3D-printed products.