Search

Vat photopolymerized 3D printing technology can be used to fabricate ceramics with complex shapes. However, the extensive use of photosensitive resins as binders is not conducive to achieving crack-free ceramic green parts, especially the Si 3 N 4 ceramics with the weak interlayer bonding. In this work, the influence of different debinding atmosphere on the pyrolysis process of organics in vat photopolymerization 3D printed Si 3 N 4 green parts was investigated. The results showed that the use of 95 vol% N 2 +5 vol% H 2 atmosphere can effectively inhibit the cracking during the debinding process, especially the wall thickness of the 3D printed defect-free Si 3 N 4 green body was successfully increased to 5 mm, and the obtained sintered Si 3 N 4 ceramics exhibited higher true densities and better mechanical properties. The debinding atmospheres proposed in the current work provided additional options of debinding atmosphere for achieving high-performance 3D printed Si 3 N 4 ceramics and are expected to be expanded to other photosensitive slurry systems, with the potential to enable the production of ceramic components with the larger wall thicknesses. [ABSTRACT FROM AUTHOR]

A Cu-coated Al 2 O 3 substrates which can be used for power modules are prepared via sintering and reduction of CuO–SiO 2 film onto the surface of Al 2 O 3 ceramic without precious metal brazing filler or high-vacuum equipment. This method has a significant cost advantage over the existing technology. Effects of oxygen partial pressure from sintering atmosphere and SiO 2 content on microstructure and mechanical properties of Cu/Al 2 O 3 interface are systematically investigated. Phase compositions and morphologies of sintered Cu 2 O layer, reduced Cu layer and reactive layer are characterized via X-ray diffraction and scanning electron microscopy. In addition, physicochemical changes within CuO–SiO 2 during sintering are characterized by thermogravimetry-differential scanning calorimeter. It is found that oxygen and SiO 2 can promote the generation of Cu 2 O–CuO–SiO 2 eutectic phase with low melting point upon sintering, which increases the thickness of reaction layer and the densification of Cu layer. The shear strength between the Cu layer and the Al 2 O 3 substrate is enhanced with the increase in Cu layer densification degree, while varying in irregular manner with the thickness of reaction layer. In particular, the highest shear strength of 62.70 MPa is obtained at oxygen partial pressure of 0.02 atm and SiO 2 content of 1.5 wt%. [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]

The development of photosensitive slurries for additive manufacturing has attracted great interest due to their correlation with the final properties of the fabricated parts. This paper focus on the printing quality control in digital light processing (DLP) 3D printing of advanced ceramics. Systematic experiments were performed to assess the effects of the exposure time and printing angle on the three-point bending strength of the fabricated samples. The exposure time affected the bending strength of the printed zirconia ceramic dramatically. When the weak exposure time is 1 s and the strong exposure time is 13 s, the average bending strength can reach 580 MPa while Weibull modulus can reach 8.84. Meanwhile, the printing angle also affected the bending strength mechanical sample printed at 45° exhibits the worst performance. [ABSTRACT FROM AUTHOR]

The high integration density of microelectronic devices leads to local heat accumulation, and effective heat dissipation and signal transmission of packaging materials have become the primary issues to be solved. However, existing polymer materials have difficulty meeting the requirements due to their unsatisfactory thermal conductivity and thermal expansion properties. In this work, we proposed the use of digital light processing (DLP) printing technology to construct a triply periodic minimum surface (TPMS) skeleton, and a continuous and efficient heat conduction path was successfully constructed in epoxy resin by impregnating h-BN on the skeleton surface. When the loading of h-BN was 20 vol%, the thermal conductivity of the TPMS(SiO 2)@BN/EP(BN) composites was 1.86 W/(m·K), which was 786 % higher than that of pure epoxy resin. In addition, the thermal expansion coefficient of the composites decreased by more than 70 %. At the test frequencies of 3∼10 MHz, the composites showed stable dielectric properties, and the dielectric constant was always maintained in a low range, between 3.85 and 4.15. This work has realized the transformation of the method for constructing a heat conduction path from disordered to ordered and from random to repeatable. This provides a new strategy for the selection of microelectronic packaging materials. [ABSTRACT FROM AUTHOR]

4H–SiC is an ideal material for micro-electromechanical system sensors used in high temperature environment due to its outstanding material properties. In this work, we systematically studied the piezoresistive characteristics of 4H–SiC with different doping concentrations in the range of 25–600 °C. We found that the piezoresistive curves of 4H–SiC with different doping concentrations show clear nonlinear fluctuations ranging from 494 to 600 °C. Moreover, as the doping concentration increases, the critical temperature point of the fluctuations gradually shifts towards higher temperature. Based on the analysis of the charge carrier transport mechanism, we found that the intrinsic excitation of 4H–SiC at high temperature can lead to nonlinear fluctuations in the piezoresistive effect, and proposed a theoretical model of piezoresistive coefficient GF of 4H–SiC under intrinsic excitation. Furthermore, the results of the variable temperature Hall effect test show that increasing the doping concentration of 4H–SiC can effectively suppress the nonlinear piezoresistive effect caused by intrinsic excitation. Based on the above investigation, we conclude that the appropriate doping concentration of 4H–SiC should range from 1018 to 1019 cm−3, which provides important reference for the selection and design of 4H–SiC chip parameters.Graphical abstract: 4H–SiC is an ideal material for micro-electromechanical system sensors used in high temperature environment due to its outstanding material properties. In this work, we systematically studied the piezoresistive characteristics of 4H–SiC with different doping concentrations in the range of 25–600 °C. We found that the piezoresistive curves of 4H–SiC with different doping concentrations show clear nonlinear fluctuations ranging from 494 to 600 °C. Moreover, as the doping concentration increases, the critical temperature point of the fluctuations gradually shifts towards higher temperature. Based on the analysis of the charge carrier transport mechanism, we found that the intrinsic excitation of 4H–SiC at high temperature can lead to nonlinear fluctuations in the piezoresistive effect, and proposed a theoretical model of piezoresistive coefficient GF of 4H–SiC under intrinsic excitation. Furthermore, the results of the variable temperature Hall effect test show that increasing the doping concentration of 4H–SiC can effectively suppress the nonlinear piezoresistive effect caused by intrinsic excitation. Based on the above investigation, we conclude that the appropriate doping concentration of 4H–SiC should range from 1018 to 1019 cm−3, which provides important reference for the selection and design of 4H–SiC chip parameters. [ABSTRACT FROM AUTHOR]