Search

In this paper, using Si₃N₄, Al₂O₃ and AlN particles as raw materials, β-SiAlON ceramics with different main crystal phases were designed. The green body of the β-SiAlON-matrix ceramic samples were obtained by using stereolithography (SLA) additive manufacturing. After degreasing, dense β-SiAlON ceramics with different SiAlON phases were fabricated through gas pressure sintering at 1800°C for 1hour at GPa. The effects of the different Al₂O₃ contents on the shrinkage, phase composition, relative density, microstructure, mechanical property and hardness were studied. The results indicate that the main phase of the ceramics was β-SiAlON and the specific chemical compositions of it were Si₅AlON₇, Si3.1Al2.9O2.9N5.1 and Si₂Al₄O₄N₄. The intergranular phases that exists were mainly Y₃Al₅O12, YAlO₃ and Al₂O₃. With a relative density of 90.03 %, the Vickers hardness (Hv5), bending strength and fracture toughness of the fabricated β-Si₅AlON₇ ceramics were 16.8 GPa, 465 MPa and 4.84 MPa.m1/2, respectively. Meanwhile, the shrinkage of the materials was 28.7 %.

In this study, four unique groups of nano-cemented carbides with 8 wt.% Co and trace amount of Mo and VC have been successfully synthesized. The effect of Mo and VC has been investigated comprehensively on both the microstructure and mechanical behavior of nano-cemented carbide. The results show that Mo significantly increases hardness but decreases the fracture toughnesses and VC slightly increases hardness and strongly increases fracture toughness of nano-cemented carbide. It is found that the optimum Mo and VC contents are both 0.5 wt.%. The average WC grain size is about 370 nm. The hardness is about 2350 HV30 and the fracture toughness is about 11.2 MPam-1/2.

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]

In this work, Al2O3-AlN composite ceramics with high bending strength and thermal conductivity were fabricated by Digital Light Processing (DLP). The influence of AlN content on the rheological and cure behavior of Al2O3-AlN suspensions, as well as the microstructure, thermal conductivity, and bending strength of Al2O3-AlN ceramics, were systematically investigated. The result shows that the viscosity and cure ability of the suspensions were decreased with the increase of AlN content, which are beneficial to the spreading and printing accuracy of the suspensions. Besides, the bending strength of ceramics can be improved due to the residual stress by the introduction of AlN. Approaches were employed to minimize the formation of AlON in Al2O3-AlN ceramics by optimizing the amount of AlN and the sintering temperature. The thermal conductivity and bending strength of Al2O3-AlN ceramics were 31.72 ± 0.45 W/(m·K) and 572.73 ± 59.40 MPa, respectively, which are much higher than those of Al2O3 ceramics fabricated under the same condition. Finally, complex-shaped Al2O3-AlN ceramics components have been successfully fabricated by DLP, which may provide an opportunity to broaden the application of Al2O3-AlN composite ceramics in heat dissipation components. [ABSTRACT FROM AUTHOR]

Enhancement of the thermal conductivity of silicon nitride is usually achieved by sacrificing its mechanical properties (bending strength). In this study, β‐Si3N4 ceramics were prepared using self‐synthesized Y3Si2C2 and MgO as sintering additives. It was found that the thermal conductivity of the Si3N4 ceramics was remarkably improved without sacrificing their mechanical properties. The microstructure and properties of the Si3N4 ceramics were analyzed and compared with those of the Y2O3‐MgO additives. The addition of Y3Si2C2 eliminated the inherent SiO2 and introduced nitrogen to increase the N/O ratio of the grain‐boundary phase, inducing Si3N4 grain growth, increasing Si3N4 grain contiguity, and reducing lattice oxygen content in Si3N4. Therefore, by replacing Y2O3 with Y3Si2C2, the thermal conductivity of the Si3N4 ceramics was significantly increased by 31.5% from 85 to 111.8Wm−1K−1, but the bending strength only slightly decreased from 704 ± 63MPa to 669 ± 33MPa. [ABSTRACT FROM AUTHOR]

Aluminum nitride (AlN) ceramics with dense structure, high thermal conductivity, and exceptional mechanical properties were fabricated by pressureless sintering with a novel non-oxide sintering additive, samarium fluoride (SmF 3). The results showed that the use of a moderate amount of SmF 3 promoted significant densification of AlN and removed the oxygen impurity. This led to the formation of fine and isolated secondary phase that cleaned the grain boundaries and increased the contact between AlN grains, remarkably enhancing thermal conductivity. Furthermore, SmF 3 also exhibited grain refinement and grain boundary strengthening effects similar to traditional sintering additive, samarium oxide (Sm 2 O 3), leading to high mechanical properties in SmF 3 -doped AlN samples. The most optimal characteristics (thermal conductivity of 190.67 W·m−1·K−1, flexural strength of 403.86 ± 18.27 MPa, and fracture toughness of 3.71 ± 0.19 MPa·m1/2) were achieved in the AlN ceramic with 5 wt% SmF 3. [ABSTRACT FROM AUTHOR]

In this work, the influence of Al-metal powder addition upon that thermal, mechanical and dielectric properties of aluminium nitride (AlN) ceramic was studied. The findings show that adding Al-metal powder improves not only the mechanical and thermal properties of the AlN ceramic but also has no negative impact on its dielectric properties. Based on Y 2 O 3 as sintering aid, the AlN ceramic with 1.0 wt% Al doping were 14.35% higher thermal conductivity, 11.73% higher flexural strength and 59.50% higher fracture toughness than those doped without Al, respectively. This study showed that the addition of Al-metal powder may favor the purifying of the AlN lattice and the formation of homogenous and isolated second phase, which would increase the AlN–AlN interfaces and improve the thermal conductivity. Furthermore, the grain boundaries of AlN ceramics might be strengthened by the isolated second phases due to the thermal mismatch between the second phases and AlN grains, thus strengthening and toughening the AlN ceramic doped with Al. However, the large additive amount of Al powder (>1.0 wt%) was not help the isolation and homogenization of the second phase, giving a deterioration in an AlN ceramic's mechanical and thermal properties. These results suggest that the introduction of an appropriate dose of aluminium metal powder is a simple method that can be used to improve the AlN ceramic's mechanical and thermal properties simultaneously. [ABSTRACT FROM AUTHOR]

In this study, we present a DLP 3D-printing strategy for the fabrication of SiCN ceramic matrix composites (CMCs). The polysilazane-based preceramic polymer containing inert fillers was UV-cured into a green body and then converted to SiCN CMCs after pyrolysis. The introduced fillers (Si 3 N 4 particles and Si 3 N 4 whiskers) as reinforcements are well dispersed in the matrix, which can not only effectively reduce the linear shrinkage and weight loss, but also greatly improve the mechanical properties of the SiCN CMCs. The bending strength of the SiCN CMCs reinforced with 10 wt% Si 3 N 4 whiskers (without surface polished) reached 180.7 ± 15.6 MPa. Furthermore, the effect of fillers content on microstructure and porosity of the SiCN CMCs are discussed, and it was found that the excessive fillers led to increased pore defects and decreased continuity of the matrix, thereby reducing the mechanical properties of the SiCN CMCs. This strategy provides a promising ceramic manufacturing technique to fabricate polymer‐derived CMCs with complex-shaped and high-performance for potential demanding applications. [ABSTRACT FROM AUTHOR]

In this study, the impact of sintering aid content and sintering time on the density, phase composition, microstructure, thermal conductivity, and mechanical properties of silicon nitride (Si 3 N 4) ceramics through vat photopolymerization (VPP) was systematically investigated. The results revealed that an increase in sintering aid amount promoted the network distribution of the grain boundary phase along with densification, grain coarsening and microstructure uniformity. The extension of sintering time improved density, thermal conductivity, and mechanical properties of the material. Superior performance with relative density of 99.4 %, thermal conductivity of 64.4 W·m−1·K−1, flexural strength of 879 ± 37 MPa, and hardness of 15.0 ± 0.4 GPa was achieved in sample containing 8 wt% MgO/Y 2 O 3 sintered for 12 h. Finally, high-precision Si 3 N 4 ceramic heat sink elements were successfully fabricated via VPP, opening up new prospects in thermal management applications associated with electronics and automotive industries. [ABSTRACT FROM AUTHOR]

Silicon nitride (Si 3 N 4) powder possesses a high refractive index and a significant ultraviolet (UV) absorptivity, consequently enabling great challenges in the fabrication of Si 3 N 4 ceramics using vat photopolymerization. The TEM, SEM, XRD and XPS results indicate that the yttrium aluminum garnet (YAG) can be coated on the surface of Si 3 N 4 ceramic powder using a non-aqueous chemical precipitation coating (NCP) process, and the effects of ceramic powder coating treatment on the curing behavior, rheological of Si 3 N 4 slurry, and the microstructure and mechanical properties of Si 3 N 4 ceramics were systematically investigated in this work, based on the detailed performance comparisons between the Si 3 N 4 samples manufactured using the NCP and traditional wet ball-milling (WBM) methods, respectively. Results demonstrated that the uniform distribution of YAG film on the surface of Si 3 N 4 powder notably can favor the enhancement of the rheological and curing behaviors of Si 3 N 4 ceramic slurries. The viscosity of NCP ceramic slurry was observed to be 42.25 % lower than that of WBM ceramic slurry at a shear rate of 35 s−1. Additionally, the cure depth of NCP ceramic slurry with the solid loading of 30 vol% at the exposure energy of 159.6 mJ/cm2 was measured to be 35.4 µm, which is 22.49 % higher than that of the WBM ceramic slurry. Moreover, compared with the WBM ceramic slurry at the same curing depth, the NCP ceramic slurry demonstrates higher precision in shaping dimensions. The bending strength and Weibull modulus of NCP-SN sample were 833.74 ± 39.35 MPa and 25.15, respectively, which were 17.64 % and 173.07 % higher than those of WBM-SN sample. This improvement is attributed to the advantageous aspects of the NCP process, which promote the uniform distribution of the liquid phase, facilitate the sintering densification of Si 3 N 4 ceramic, and accelerate the formation of elongated crystalline grains. Ultimately, superior-quality Si 3 N 4 components with distinct contours were successfully fabricated. The methodology proposed in this work contributes to advancing the rapid manufacturing and performance optimization of the intricately structured Si 3 N 4 ceramic components. [ABSTRACT FROM AUTHOR]

5 wt% of different types of rare earth oxides (Re 2 O 3 , Re = Lu, La, Yb, Y, Nd, Er, Sm, Ce, Dy, Eu, Gd) and 2 wt% MgO as additives were selected in this study based on previous studies on rare earth oxide additive concentrations. The effects of rare earth oxide type on the microstructure, phase composition, thermal conductivity, mechanical properties, and dielectric properties of silicon nitride ceramics were systematically investigated. Samples doped with rare earth oxides with smaller ionic radii (such as Yb 2 O 3 , Lu 2 O 3 , Er 2 O 3 , and Dy 2 O 3) showed higher thermal conductivity. Samples doped with Eu 2 O 3 and Yb 2 O 3 showed fine-grained microstructures due to inhibition of dissolution, diffusion, and re-precipitation of silicon nitride. Silicon nitride ceramics doped with Eu 2 O 3 showed the lowest thermal conductivity and dielectric constant (<8) compared to the other samples. Samples doped with Y 2 O 3 showed the maximum fracture toughness of 8.4 MPa m1/2. Meanwhile, it was observed that the addition of rare earth oxides with the largest (La 2 O 3), moderate (Eu 2 O 3), and smallest (Lu 2 O 3) ionic radii could all effectively improve the fracture toughness of silicon nitride ceramics. Samples doped with rare earth oxides with large ionic radii, such as Nd 2 O 3 , Ce 2 O 3 , and La 2 O 3 , had larger dielectric constants. The dielectric loss of silicon nitride ceramics prepared here was between 0.005 and 0.02 and dependence on the type of rare earth oxide was not observed. [ABSTRACT FROM AUTHOR]

In this research, we creatively integrate the traditional methods of liquid precursor infiltration plus in-situ precipitation with stereolithography-based 3D printing for the fabrication of Al 2 O 3 -ZrO 2 ceramics to ensure the homogeneous distribution of ZrO 2 particle in the alumina matrix. Our characterization results shows that this combination leads to the materials with significantly better performance. The Al 2 O 3 specimen is soaked in a Zr 4+ ion solution to induce infiltration, in-situ precipitation and then sintered. X-ray diffraction analysis of the thus-treated sample indicated that Al 2 O 3 was the primary phase and t-ZrO 2 was the secondary phase. Microstructural and EDS analysis showed that the ZrO 2 particles were homogeneously distributed in the Al 2 O 3 matrix, leading to inhibited grain growth. The samples soaked in solutions for different Zr 4+ concentrations and sintered both at 1450 °C and 1550 °C showed improved mechanical properties as compared to those of pure alumina. Futhermore, the sample infiltrated using the solution with a concentration of 1.5 mol/L and sintered at 1450 °C showed similar fracture toughness (4.97 MPa m 1/2 ) with the sample sintered at 1550 °C (5.06 MPa m 1/2 ) but much better hardness (20.95 Gpa) than the sample sintered at 1550 °C (19.71 GPa). Therefore, this method could not only enhance the mechanical properties via introducing the second phase, but also lowers the sintering temperature by at least 100 °C, which would be beneficial for energy conservation and leads to significant advances in the 3D printing of ceramic components. [ABSTRACT FROM AUTHOR]

In this paper, a ceramic suspension with appropriate viscosity was prepared by optimizing the powder solid content and the dispersant content. An Al 2 O 3 -ZrO 2 ceramic green body was fabricated using the SLA technique, followed by the application of a liquid drying and two-step debinding process to prepare the defect-free Al 2 O 3 -ZrO 2 ceramic green body. The relative density, phase composition, microstructure, grain size, and mechanical properties of Al 2 O 3 -ZrO 2 samples sintered at different temperatures were compared. The main results indicated that the sample density increased with the sintering temperature until reaching a maximum density of 4.28 g/cm 3 at 1600 °C. When the temperature further increased to 1650 °C, the density dropped instead. With increasing sintering temperature, both the number of grain boundaries and the number of pores located at the grain boundaries reduced greatly. The Vickers hardness of the samples first increased and reached its maximum at 1550 °C with a value of 17.6 GPa, and then decreased with further increases in sintering temperature. The fracture toughness increased with the sintering temperature and reached a maximum value of 5.2 MPa·m 1/2  at 1650 °C. A sintering kinetics window which could offer the relationship between the sintering temperature and the relative density & grain size was set and also the microstructure evolution of the sintered body was conducted to get a deeper understanding of the 3D printing Al 2 O 3 -ZrO 2 composites. [ABSTRACT FROM AUTHOR]

Ceramic-metal composite materials, namely cermets, are provided with characteristics of both ceramic and metal. Herein, for the first time bio-cermets based on β-tricalcium phosphate (β-TCP) bioceramic with biodegradable iron being reinforcement phase, were fabricated using the powder metallurgic method. The phase composition, microstructure, mechanical properties and in vitro cell behaviors of bio-cermets were investigated. The results revealed that atomic diffusion occurred between the iron and β-TCP matrix during the sintering process. The bio-cermets attained remarkable increase in fracture toughness (1.16–1.55 MPa m 1/2 ) compared to the β-TCP bioceramic (0.54 MPa m 1/2 ). The bio-cermets with 10 vol% iron showed the highest compressive strength (640 MPa), significantly higher than that of plain β-TCP bioceramic (285 MPa). The in vitro cell behaviors test indicated that the bio-cermets did not showed any sign of toxicity; the iron ions released from bio-cermets up-regulated bone-related gene expression of bone mesenchymal stem cells. The bio-cermets developed in this study represent potential bone substitutes for application in the load-bearing bone defects. [ABSTRACT FROM AUTHOR]

Silicon nitride (Si 3 N 4 ) ceramics offer excellent thermal, mechanical and dielectric properties, which make Si 3 N 4 a good candidate material for an application as electronic packaging material. For an application as a heat dissipation substrate, most studies focused on achieving a high thermal conductivity through long-time heat preservation and different kinds of heat treatments. Very few studies also considered the mechanical and dielectric properties. In addition, there have not been systematic researches about influence of additives concentration and type on the combination properties of Si 3 N 4 . Therefore, in this study, Si 3 N 4 ceramic samples were prepared via hot pressing at 1800 °C with a relatively short heat preservation step (2 h), with different amounts of Y 2 O 3 added as sintering additive. The effect of the initial concentration of the rare earth oxide on the chemical composition, microstructure, thermal conductivity, as well as the mechanical and dielectric properties of the Si 3 N 4 ceramic samples was systematically studied. [ABSTRACT FROM AUTHOR]