Characterization of Interfaces Between Layers of Differently Sized Particles in Pressure-Assisted Binder Jetting

This study aims to quantify the interfaces between adjacent layers of differently sized particles fabricated using a pressure-assisted binder jet additive manufacturing (AM) process. Sugar particles are used as model material, which has been widely studied as a simulant for energetic materials. A particle coloring approach was employed to visualize the intermixing zone between layers, enabling quantification of key interface characteristics, including intermixing thickness and porosity. By changing the binder concentration in the adjacent layers, the profile of the interface varies, e.g., from a narrow, straight, horizontal band to a thick, gradient, jagged region. A low binder concentration in fine particles resulted in brittleness and more resistance to particle rearrangement, restricting large particle penetration into the fine particle layer under pressing and leading to a thinner, sharper intermixing zone. In contrast, a high binder concentration in fine particles yields a ductile, deformable microstructure, promoting fine particle rearrangement, large particle penetration, and a thicker intermixing zone. Tensile tests, in situ optical imaging, and digital imaging correlation (DIC) were conducted to analyze the mechanical behavior of the interfaces. Crack initiation and propagation along the interface have not been observed, suggesting that the intermixing of particles at the interface not only preserved the mechanical performance but also enhanced it beyond that of the neighboring layers. This research provides insights into the interaction between differently sized particles being pressed into each other and the effect of binder concentration on interfacial characteristics in pressure-assisted binder jetting, advancing understanding of microstructures and properties in additively manufactured multi-material composites.