碳纤维增韧增强氮化硅陶瓷基复合材料力学性能的数值模拟

基于Tanake-Mori基体平均应力以及Eshlby等效夹杂法，提出了1种求连续相材料的应力和应变的近似理论，由此可精确评估两相和3相复合材料的力学性能。本文利用计算机模拟对碳纤维增韧的氮化硅复合材料（Cf/Si3n4)的弹性模量、剪切模量和泊松比进行理论计算，从其内部微观结构出发，探讨了不同相含量、气孔的含量以及形状等复合材料力学性能的影响。     

Electromagnetic wave absorption properties of hot-pressed Si3N4-SiC ceramic nanocomposites

High-density Si₃N₄-SiC ceramic nanocomposites have exceptional mechanical properties, but little is known about their electromagnetic wave absorption (EMA) capabilities. In this paper, the effects of sintering temperature and starting material compositions on the dielectric and EMA properties of hot-pressed Si₃N₄-SiC ceramic nanocomposites were investigated. The real and imaginary permittivities of Si₃N₄-SiC ceramic nanocomposites increase with increasing sintering temperature or SiC content, particularly at the sintering temperature of 1850°C and SiC content of 50 wt.%. This is primarily due to the improvement of interfacial and defect polarizations, which is caused by the doping of nitrogen into the SiC nanocrystals during the solution-precipitation process. The real and imaginary permittivities of Si₃N₄-SiC ceramic nanocomposites show decreasing trends as sintering aid content increases. Si₃N₄-SiC ceramic composites have both good EMA and mechanical properties when they are sintered at 1850°C with 30 wt.% SiC and 5–8 wt.% sintering aids. The minimum reflection loss and maximum flexural strength reach -58 dB and 586 MPa, respectively. Materials with multilayered structural designs have both strong and broad EMA properties.     

常压烧结氮化硅陶瓷的研究

本文研究了常压烧结Si3N4-MgO-Y2O3-La2O3系Si3N4陶瓷。测试了材料的密度和力学性能．分析了其物相组成和显微结构。研究表明：MgO—Y2O3-La2O3组成的复合烧结助剂能有效降低Si3N4的烧结温度、促进Si3N4的致密化，其烧结机理为液相烧结；随着La2O3与Y2O3比（La2O3：Y2O3）的增加，材料的致密度、强度、硬度和断裂韧性都先增加后减小，当La2O3：Y2O3=1：1时达到最大值。     

新型Si3N4/TiCnano复合陶瓷材料的制备及性能

本文利用热压烧结方式制备了新型Si3N4/TiCnano复合陶瓷材料,对材料的配方及烧结工艺进行了优化,采用XRD、SEM等手段分析了材料的微观结构,研究了烧结条件对材料性能的影响机理。结果表明,所研究的材料具有良好的力学性能。     

流延法在Si3N4块体及Si3N4/BN层状材料制备中的应用

本采用流延法制备了Si3N4块体及Si3N4/BN层状材料,流延法已经在陶瓷的制备工艺中得到了广泛的应用,但是很少用于Si3N4体系,尤其是水基流延法。用流法制备Si3N4/BN层状材料时,可以较为容易地控制坯片的厚度,得到性能稳定的层状材料。     

Preparation and properties of lightweight,conformal, and load-bearing TiC/Si3N4 absorbing composites by gel casting

In view of the lack of conformal, load-bearing, light-weight, and high temperature-resistant integrated wave-absorbing composites suitable for extremely complex conditions, the gel-casting process was successfully applied to porous Si₃N₄ wave-absorbing composites in this work. A universal low-slurry for gel casting was prepared by using two dispersants acting together (tetramethylammonium hydroxide solution and sodium lauryl sulfate), which ensured the smooth completion of the gel casting process. Combining the thermogravimetric and differential thermal gravity curves of the composite green body, reasonable parameters of the rubber discharge process are given to avoid the problem of the green body swelling and cracking. The porous TiC/Si₃N₄ composites were successfully prepared by holding them at 1650°C for 3 h. The bending strength, density, minimum reflection loss, absorption bandwidth, and matched thickness in the P-band of the composites with 30 wt.% TiC addition were 54.08 ± 3.02 MPa, 1.906 g/cm³, -37.75 dB, 1.9 GHz, and 4.1 mm, respectively. The electromagnetic wave loss mechanisms of the composites are a combination of conductivity loss, multiple reflections and scattering, interfacial polarization, and defect polarization.     

Fabrication and properties of surface‐modified β‐Si3N4 whiskers reinforced dental resin composites

In this article, three kinds of surface‐modified methods were used to treat β‐Si₃N₄ whiskers before being incorporated into Bis‐GMA/TEGDMA dental resin matrix in order to improve the whiskers' reinforcing effect. The experimental results showed that composites with directly heat‐treated and then silanized β‐Si₃N₄ whiskers had the best reinforcing effect. They had flexural strength of 160 ± 7.0 MPa (mean ± SD; n = 6), compressive strength of 371 ± 1.4 MPa (mean ± SD; n = 5) and HRA of 48.4 ± 0.5(mean ± SD; n = 5), respectively. In addition, water sorption and solubility test demonstrated that the composites were reliable to use as the dental restoration materials. Therefore, the directly heat‐treated and then silanized β‐Si₃N₄ whiskers (better than β‐Si₃N₄ whiskers mixed with SiO₂ nanoparticles or SiO₂ sols) were most suitable fillers to reinforce dental resin composites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Multiscale designed SiCf/Si3N4 composite for low and high frequency cooperative electromagnetic absorption

With the aim to design a particular material for low and high frequency cooperative electromagnetic absorption at high temperature, a multiscale design is proposed by combining the microstructure and meta‐structure in one material. The SiC_f/Si₃N₄ composite is prepared via the chemical vapor infiltration technique with SiC_f as the EM wave absorbing phase and Si₃N₄ as the wave‐transparent ceramic matrix. The crossing grooved meta‐structure is designed and fabricated to further improve its absorbing properties and to guarantee its absorbing capacity stability at high temperature. A minimum reflection loss of ?15.3 dB and ?14.8 dB can be reached at 8 and 18 GHz with a total thickness of 5 mm. The temperature‐dependent reflection loss of the designed meta‐structure keeps relative reliable high temperature absorbing performances from room temperature to 500°C. This effective enhanced EM wave absorbing property is believed to be a consequence of multiscale effect induced by combining the traditional EM absorbing materials with metamaterial structure.     

Cup-stacked carbon nanotubes hybridized Si3N4/Si3N4 composite ceramics for high-effciency microwave absorption with excellent thermal stability

Hybridization between carbon nanotubes (CNTs) and Si₃N₄ is a promising strategy for developing high-temperature microwave absorption (MA) materials for military application. Toward long-life services, it's important to achieve strong MA at a filler loading as low as possible on account of antioxidant protection against CNTs wastage. Herein, cup-stacked CNTs (CSCNTs) have been prepared in porous Si₃N₄ ceramics by chemical vapor deposition (CVD) and then CVD Si₃N₄ has been coated on them, forming CSCNT-Si₃N₄/Si₃N₄ composite ceramics. Results show that CSCNTs possess abundant exposed atomic edges on the outer surface and in the inner channel. Such unique defects not only benefit the impedance match but also cause considerable conductive loss, which helps CSCNT-Si₃N₄/Si₃N₄ with a filler content of only 0.79 wt% to achieve an effective absorption bandwidth (EAB) of 3.74 GHz in the X band at a thickness of 3.5 mm coupled with a minimum reflection loss of ?43.3 dB and an EAB covering the entire Ku band at a thickness of 2.25 mm. The ultralow filler loading generates a high efficiency of CVD Si₃N₄ in protecting CSCNTs against high-temperature oxidation, leading to a steady MA performance for CSCNT-Si₃N₄/Si₃N₄ during 23–1200 °C thermal shock tests in air.     

Si3N4含量对Si3N4-SiC材料腐蚀性能的影响

利用Si3N4—SiC材料在冰晶石静态融盐电解质中的腐蚀实验研究材料的腐蚀性能,对腐蚀增重率进行记录分析,Si3N4的含量是影响材料腐蚀性能的重要因素,根据实验测定得出Si3N4的含量越高,Si3N4-SiC材料腐蚀程度越严重。     

3D printing of honeycomb Si3N4 ceramic

In this paper, a honeycomb Si₃N₄ ceramic was fabricated by 3D printing with a well-preserved structure. The effects of Si₃N₄ content on the rheological properties of Si₃N₄/sol–silica ink and the printing resolution of products were investigated. The microstructure, phase composition, liner shrinkage rate, and fracture behavior of printed samples before and after sintering were systematically characterized in detail. The results showed that the modified inks had the optimized rheological properties, and the stress–shear rate curves corresponding to each slurry could be well described by Bingham and Herschel–Bulkley fluid models. The corresponding slump rates of the printed samples with different Si₃N₄ to sol–silica mass ratios were all lower than 4%, and the linear shrinkage rate of all of the samples after sintering was below 20%. The fracture behavior under compressive loading of the honeycomb Si₃N₄ ceramics tended to be non-catastrophic fractures both before and after sintering. The compressive strengths of all of the printed samples decreased with the increase of the Si₃N₄ content, and the highest compressive strength of the honeycomb ceramics could reach 131.2 MPa after sintering at 1600°C, which was about 366.9% higher than that of the samples in green state prior to the sintering.     

Microstructure and EMW absorption properties of CVI Si3N4–SiCN ceramics with BN interface annealed in N2 atmosphere

A kind of chemical vapor infiltration (CVI) Si₃N₄–BN–SiCN composite ceramic with excellent electromagnetic wave (EMW) absorbing properties is obtained by CVI BN interface and SiCN matrix on porous Si₃N₄ ceramics, and then annealed at high temperatures (1200°C‐1500°C) in N₂ atmosphere. The crystallization behavior, EMW absorbing mechanism and mechanical properties of the composite ceramics have been investigated. Results showed CVI SiCN ceramics with BN interface were crystallized in the form of nanograins, and the crystallization temperature was lower. Moreover, both EMW absorbing properties and mechanical properties of CVI Si₃N₄–BN–SiCN composite ceramics firstly increased and then decreased with the increase in annealing temperature due to the influence of BN interface on the microstructure and phase composition of the composite ceramics. The minimum reflection coefficient (RC) and maximum effective absorption bandwidth (EAB) of the composite ceramics annealed at 1300°C were ?47.05 dB at the thickness of 4.05 mm and 3.70 GHz at the thickness of 3.65 mm, respectively. The flexural strength and fracture toughness of the composite ceramics annealed at 1300°C were 94 MPa and 1.78 MPa/m^1/2, respectively.     

氮化硅陶瓷的应用和酸腐蚀研究进展

综述了氮化硅陶瓷的三种工业应用,即氮化硅陶瓷轴承球、氮化硅涡轮转子、铝冶金氮化硅陶瓷部件,以及氮化硅在H2SO4,HN03,HCl,HF等酸溶液及高温SO2和HCl气体中的腐蚀行为,对其腐蚀机理进行总结,并提出今后提高氮化硅陶瓷抗腐蚀性能的研究重点。     

Si3N4／SiC纳米复相陶瓷研究进展

本文综述了Ｓｉ３Ｎ４／ＳｉＣ纳米复相陶瓷的研究进展,较详细地介绍了纳米粉体的制备工艺及热处理研究、复相陶瓷的制备工艺、力学性能、微观结构及增韧强化机理。     

Effect of interphase on mechanical properties and microstructures of 3D Cf/SiBCN composites at elevated temperatures

Interphase between the fibers and matrix plays a key role on the properties of fiber reinforced composites. In this work, the effect of interphase on mechanical properties and microstructures of 3D C_f/SiBCN composites at elevated temperatures was investigated. When PyC interphase is used, flexural strength and elastic modulus of the C_f/SiBCN composites decrease seriously at 1600°C (92 ± 15 MPa, 12 ± 2 GPa), compared with the properties at room temperature (371 ± 31 MPa, 31 ± 2 GPa). While, the flexural strength and elastic modulus of C_f/SiBCN composites with PyC/SiC multilayered interphase at 1600°C are as high as 330 ± 7 MPa and 30 ± 2 GPa, respectively, which are 97% and 73% of the values at room temperature (341 ± 20 MPa, 41 ± 2 GPa). To clarify the effect mechanism of the interphase on mechanical properties of the C_f/SiBCN composites at elevated temperature, interfacial bonding strength (IFBS) and microstructures of the composites were investigated in detail. It reveals that the PyC/SiC multilayered interphase can retard the SiBCN matrix degradation at elevated temperature, leading to the high strength retention of the composites at 1600°C.     

Si3N4-SiC材料的氧化性能研究

通过对不同Si3N4含量、不同温度下Si3N4-SiC材料的氧化实验,分析氧化后的氧化增重率,得出Si3N4含量越高,材料氧化越严重;氧化温度越高,材料氧化越严重;且氧化增重率与氧化时间呈直线-抛物线规律。     

Preparation and characterization of polymer-derived Zr/Si/C multiphase ceramics and microspheres with electromagnetic wave absorbing capabilities

Precursors for Zr/Si/C multiphase ceramics were synthesized by the reactions of dilithiozirconocene complex with dichlorodimethylsilane, methyltrichlorosilane and dichloromethylvinylsilane, respectively. The precursor-to-ceramic process of the precursor was investigated by TG-GC–MS and TG-FTIR analyses, confirming a complete transformation from organometallic polymers into ceramics below 800 °C. Annealing experiments of the derived ceramics at temperatures from 1000 °C to 2000 °C indicated the crystallization from ZrSiO₄, ZrO₂ to ZrC. Furthermore, micrometer-sized Zr/Si/C ceramic microspheres were successfully fabricated from the precursor at 1000 °C, showing surface morphology like wrinkled pea. According to the XRD, HRTEM and XPS analyses, such multiphase ceramic microspheres consist of ZrSiO₄, ZrO₂, and amorphous SiO_xC_y. Interestingly, the ceramic microspheres performed satisfactory electromagnetic wave absorbing capacity with the RL_max reaching −34 dB, which could be potential candidates for electromagnetic micro-devices.     

纳米氮化硅粉体的制备

本文用碳热还原法制备了纳米氮化硅粉体,研究了纳米氮化硅颗粒的表面形貌及其电子自旋共振谱。     

Si3N4陶瓷常压烧结研究进展

论述了Si3N4陶瓷常压烧结过程中助烧剂的选择，烧结机理和高温性能改善方面的研究进展。     

Temperature-driven wear behavior of Si3N4-based ceramic reinforced by in situ formed TiC0.3N0.7 particles

Si₃N₄ as a structural ceramic is desirable for applications in spacecraft, transportation, and energy, but its poor high-temperature properties still do not satisfy the actual requirements. Here, a TiC_0.3N_0.7 reinforced Si₃N₄ ceramic is successfully designed and fabricated via the high-temperature nitridation of TiC_x. It is found that TiC_0.3N_0.7 grains with the size of 1-2 μm are uniformly dispersed in the Si₃N₄ matrix and show a firm bond with substrate. Compared with pure Si₃N₄, the doping of harder TiCN phase can effectively improve ceramic's hardness and fracture toughness at a certain temperature. Importantly, the ceramic material displays extraordinary wear resistance across a wide temperature range (eg, the wear rate of TiC_0.3N_0.7 containing Si₃N₄ over 63 times and 178 times better than pure Si₃N₄ at 600 and 900°C, respectively). More broadly, a correlation between wear mechanism and temperature is established, and the result shows that the mechanical strength and tribochemical oxidation as two key factors determine the wear behavior of the material. These results developed here can provide a springboard for preparation and optimization of multiphase ceramics that serve under high-temperature conditions.