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The silicon nitride (Si3N4) possessing enhanced thermal conductivity and flexural strength was sintered by a hot‐pressing flowing sintering (HPFS) method. The effects of extrusion deformation and sintering additives on the density, phase, microstructure, and performances of Si3N4 fabricated by HPFS were investigated. As the strain increased from 67% to 167%, the mean grain diameter of Si3N4 with MgSiN2 as an additive increased by 49%, reaching 1.36 ±.6 µm. The addition of MgSiN2–Y2O3 resulted in a significantly stronger degree of texturing and smaller grain diameter in Si3N4, compared to the incorporation of MgSiN2 alone. The thermal conductivity of Si3N4 with added MgSiN2–Y2O3 increased to 109.1 W m−1 K−1 in the flow direction, and the flexural strength reached the maximum value of 1250.8 ± 39 MPa in the hot‐pressing direction. The results showed that the thermal conductivity and flexure strength of Si3N4 were enhanced due to the formation of texture and the reduction of flaws induced by HPFS. Moreover, HPFS method exhibited outstanding controllability over the microstructures and properties of materials. [ABSTRACT FROM AUTHOR]

Due to high light absorption and high refractive index of silicon nitride (Si3N4) ceramic, it is difficult to prepare Si3N4 slurry with favorable curing ability, high solid loading and low viscosity at the same time, and thus the high-quality Si3N4 parts are hard to fabricate via Digital Light Processing (DLP). In this paper, the oxidation process was used to enhance the curing behavior of Si3N4 slurry, and then silane coupling agent (KH560) was used to improve the rheological properties of the oxidized Si3N4 slurry. The effect of Si3N4 slurry with oxidation and modification on its rheological behavior, light absorption, curing ability and stability have been systematically investigated. A Si3N4 slurry with abundant photocuring ability, high solid loading, low viscosity and reliable stability was fabricated by the oxidized (1 h) and KH560 (1 wt.%) modified Si3N4 powders, and the dense Si3N4 ceramic parts were produced by this slurry via DLP 3D printing. Subsequently, the influence of oxidation and modification on microstructure, mechanical properties and thermal conductivity have been investigated. Finally, the microstructure and performances of Si3N4 ceramic were compared between different forming processes (including: DLP and cool isostatic pressing). [ABSTRACT FROM AUTHOR]

In this work, we report a novel approach to fabricate titanium carbide (TiC) ceramics toughened by Y2O3introduced via chemical precipitation method. TiC ceramics with and without Y2O3addition were consolidated by SPS, and the densification, microstructure and fracture toughness were investigated. Compared to the additive-free counterpart, improved density and finer grain microstructure were found for TiC ceramics with Y2O3sintered at 1600 °C, indicating that Y2O3additive homogeneously scattered in TiC matrix could not only improve the density but also inhibit grain growth. In addition, the grain boundary was strengthened due to Y2O3pinning in grain boundary, leading to a fracture behaviour transformation from intergranular type to the mixed mode of intergranular and transgranular fracture. Because of the improved density and strengthened grain boundary, the fracture toughness increased from 4.3 to 5.3 MPa·m1/2, which is improved by ~23% compared with that of additive-free TiC sample. [ABSTRACT FROM PUBLISHER]

Piezoelectric arrays are widely used in non-destructive detecting, medical imaging and therapy. However, limited by traditional manufacturing methods, the array's element is usually designed in simple geometry such as a cube or rectangle, restricting potential applications of the array. This work demonstrates an annular piezoelectric array consisting of different concentric elements printed by Mask-Image-Projection-based Stereolithography (MIP-SL) technology. The printed array displays stable piezoelectric and dielectric properties. Compared to a traditional single element transducer, the ultrasonic transducer with printed array successfully modifies the acoustic beam and significantly improves spatial resolution. [ABSTRACT FROM AUTHOR]

A powder mixture was prepared using α-phase-rich silicon nitride (Si 3 N 4 ) as the major raw material, with Yb 2 O 3 as an additive. These powders were fired at 1650–1750 °C for 1.5 h at nitrogen pressures of 1.0 and 0.7 atm, respectively. The effects of firing temperature and nitrogen pressure on the crystalline phase and microstructural evolution of β-Si 3 N 4 particles were investigated in detail by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and transmission electron microscopy (TEM), and corresponding mechanisms were also discussed. Electronic microscopy analyses show that the transformation and grain growth rate from α- to β-Si 3 N 4 phase was much faster at a nitrogen pressure of 0.7 atm than that of the samples fired at a nitrogen pressure of 1.0 atm. As a result, β-Si 3 N 4 whiskers with diameters of 0.1–0.5 µm and aspect ratios of 30–40 were easily obtained after firing at 1750 °C with 2.0 wt% Yb 2 O 3 as additive under a nitrogen pressure of 0.7 atm. These results suggest that the present method could potentially provide a simple, promising, and cost-effective route for the preparation of β-Si 3 N 4 whiskers. [ABSTRACT FROM AUTHOR]