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In this study, Al 2 O 3 honeycomb sandwich structures with different core geometries (square, triangular, circular) have been fabricated through an additive manufacturing system based on the stereolithography (SLA) method. The debinding procedure was performed under both nitrogen and air atmospheres. The impacts of the debinding atmosphere and core geometry on the densification and mechanical properties were investigated. The stiffness and flexural strength of the ceramics were examined experimentally using an impulse excitation of vibration technique and a three-point bending test, respectively. The specific stiffness and specific strength of the ceramics were also evaluated, with the core geometries taken into consideration. The outcomes showed that higher densification was achieved when the ceramics were exposed to debinding in nitrogen. The stiffness values were found to be similar for the same debinding condition within the honeycomb sandwich structures, irrespective of the core geometry. Notably, the highest specific stiffness (98 MNm/kg) was achieved for the samples subjected to debinding in nitrogen with a square core geometry. Furthermore, ceramics with square cores for debinding in a nitrogen atmosphere also demonstrated the highest performance in terms of specific strength (110 kNm/kg) within the honeycomb structures. This study demonstrated that Al 2 O 3 honeycomb sandwich structures with square cores may be suitable candidates for lightweight-structure demanding applications. [ABSTRACT FROM AUTHOR]

Recrystallized SiC (R–SiC) honeycomb ceramics were prepared using Al 4 SiC 4 as additives through a two–step sintering process, consisting of pre–nitridation treatment at 1800 °C for 180 min, followed by heat treatment for 60 min at temperatures ranging from 2000 to 2200 °C. The influences of firing temperature on phase compositions, microstructures, porosity, and mechanical properties of honeycomb ceramics were evaluated. The results revealed that AlN, SiC, and C were formed in situ after nitriding at 1800 °C. As the subsequent heat treatment temperature increased from 2000 to 2200 °C, the sublimation rate of submicron SiC increased, as well as AlN solid solubility. AlN diffused into SiC lattice and formed the SiC–AlN solid solution, which accelerated the conversion of 6H–SiC to 4H–SiC. According to first–principles calculations, the formation of solid solution contributed to the sintering process, which performed through the reduction of the surface energy of the grains. In addition, the pore size of specimens increased with elevating the heating temperature, and the distribution transitioned from unimodal to bimodal. Simultaneously, AlN and C activated the SiC lattice and facilitated mass transfer rate. The SiC sintering necks were well–developed at 2200 °C, resulting in the optimized overall performance of SiC honeycomb ceramics with a porosity of 52.7% and compressive strength of 17.98 MPa. [ABSTRACT FROM AUTHOR]

Inspired by the double-helix structure of biological DNA, low-volume fraction and high-strength Al 2 O 3 twisted honeycomb structures with characteristics similar to those of helical structures in the z -axis were prepared by digital light processing 3D printing technology. As the twist angle increased, the compressive strength of the fabricated Al 2 O 3 structure decreased, and the deformation mechanism of the Al 2 O 3 structures gradually changed from stretching-dominated to bending-dominated, which can be predicted by the Gibson–Ashby model. The relationship between the effective elastic modulus and the volume fraction that can be modified by varying the wall thickness was described by the Pabst–Gregorova exponential relationship. The compressive strength of the Al 2 O 3 structure with a twist angle of 0° can reach 62.4 MPa at a volume fraction of 13.3%, providing guidance to optimize lightweight structures of ceramics. [ABSTRACT FROM AUTHOR]