High porosity (40% to 60%) 316L stainless steel containing well-interconnected open-cell porous structures with pore openness index of 0.87 to 1 were successfully fabricated by binder jetting and subsequent sintering processes coupled with a powder space holder technique. Mono-sized (30 µm) and 30% (by volume) spherically shaped poly(methyl methacrylate) (PMMA) powder was used as the space holder material. The effects of processing conditions such as: (1) binder saturation rates (55%, 100% and 150%), and (2) isothermal sintering temperatures (1000 ^○C to 1200 ^○C) on the porosity of 316L stainless steel parts were studied. By varying the processing conditions, porosity of 40% to 45% were achieved. To further increase the porosity values of 316L stainless steel parts, 30 vol. % (or 6 wt. %) of PMMA space holder particles were added to the 3D printing feedstock and porosity values of 57% to 61% were achieved. Mercury porosimetry results indicated pore sizes less than 40 µm for all the binder jetting processed 316L stainless steel parts. Anisotropy in linear shrinkage after the sintering process was observed for the SS316L parts with the largest linear shrinkage in the Z direction. The Young’s modulus and compression properties of 316L stainless steel parts decreased with increasing porosity and low Young’s modulus values in the range of 2 GPa to 29 GPa were able to be achieved. The parts fabricated by using pure 316L stainless steel feedstock sintered at 1200 ^○C with porosity of ~40% exhibited the maximum overall compressive properties with 0.2% compressive yield strength of 52.7 MPa, ultimate compressive strength of 520 MPa, fracture strain of 36.4%, and energy absorption of 116.7 MJ/m³, respectively. The Young’s modulus and compression properties of the binder jetting processed 316L stainless steel parts were found to be on par with that of the conventionally processed porous 316L stainless steel parts and even surpassed those having similar porosities, and matched to that of the cancellous bone types.

The ceramic material Silicon carbide (SiC) has significant potential for applications in stereolithography apparatus (SLA) manufacturing technology. Nevertheless, SiC ceramic composites are severely limited in their applications due to their high absorption. In this paper, a surface modification process for the sol-gel method is discussed. The Al2O3 coating layer was successfully coated on the surface of SiC particles and the effect of alumina coating amount on the material properties was systematically investigated. By combining Bruggeman's effective medium theory model analysis, the regulation mechanism of the coating layer on its light scattering behavior was verified. Experimental and model analysis demonstrated that the Al2O3 coating effectively reduces the absorbance and viscosity of SiC ceramic materials while significantly enhancing the curing thickness and solids content of the ceramic slurry through the SLA process. Both the theoretical model and experimental data showed a consistent decrease in the extinction coefficient, confirming the coating layer's inhibitory effect on light absorption. When the solid content of the ceramic slurry was 72 wt%, the viscosity of the slurry was 0.84 Pa·s (shear rate of 30 s-1), and the curing thickness of the monolayer was 153 ± 10 μm. The final SiC ceramic composites, with a density of 2.67 g/cm3 and an average flexural strength of 44.7 ± 1.9 MPa, were obtained after degreasing and sintering. In this research, a novel approach is developed for the broad application of non-oxide ceramic composites, such as SiC fabricated by SLA, thereby paving the way for their expanded use.

To achieve the synergistic optimization of flexural strength and thermal expansion coefficient (TEC) in ceramic composites, a coupled predictive model based on Eshelby’s equivalent inclusion theory and Mori–Tanaka homogenization theory is established for two-phase composites. The flexural strength model incorporates matrix damage, interfacial debonding, and particle fracture, while the TEC model further considers the interfacial phase. Si3N4/MAS (Cordierite) composites with different MAS contents are fabricated by vacuum hot-press sintering for validation. The effects of MAS content on the phase composition, microstructure, relative density, and mechanical properties of the composites are investigated. The results show that the model predicts an optimal MAS content range of 18.5–24.5 vol.% under the dual requirements of high strength and low TEC. The optimal comprehensive performance is achieved at 20 vol.% MAS. For this composition, the relative density, Vickers hardness, fracture toughness, and flexural strength reach 99.03 ± 0.12 %, 14.99 ± 0.08 GPa, 6.03 ± 0.16 MPa·m1/2, and 493.67 ± 47.62 MPa, respectively. XRD and SEM analyses indicate that appropriate MAS addition promotes α→β phase transformation, densification, and the formation of elongated β-Si3N4 grains. The enhanced properties are mainly attributed to residual compressive stresses induced by thermal expansion mismatch, together with crack deflection, interfacial debonding, grain bridging, and grain pull-out mechanisms. The proposed model provides theoretical guidance for the design of ceramic composites with high strength and low TEC.