Microstructure of Si3N4-TiN composites prepared by chemical-vapour deposition

The shapes and the distribution of TiN within Si₃N₄-TiN composites prepared by the chemical-vapour deposition of a SiCl₄-TiCl₄-NH₃-H₂ system have been examined using an electron microscope. The TiN dispersion in the amorphous Si₃N₄ matrix was granular and its maximum size was 3 nm. The TiN dispersions in- and-Si₃N₄ matrices were contained in their respective crystal grains; however, the shape of the TiN dispersions in the-Si₃N₄ matrix was markedly different from that in the-Si₃N₄ matrix. Granular TiN dispersions with an average size of 10 nm were observed in the-Si₃N₄ matrix. On the other hand, the TiN dispersions in the-Si₃N₄ matrix were columnar with a diameter of several nm having its axis extended to the direction parallel to thec-axis of the-Si₃N₄ crystal.     

Preparation and some properties of chemically vapour-deposited Si3N4-TiN composite

Chemically vapour-deposited (CVD) Si₃N₄-TiN composite (a plate with the maximum thickness of 1.9 mm) has been prepared on a graphite substrate using a mixture of SiCl₄, TiCl₄, NH₃ and H₂ gases. The CVD was carried out at deposition temperatures,T _dep, in the range of 1050 to 1450 ° C, total gas pressures,P _tot, from 1.33 to 10.7 kPa and gas flow rates of 136 (SiCl₄), 18 (TiCl₄), 120 (NH₃) and 2720 (H₂) cm³ min^–1. The deposits thus obtained appeared black. The Ti content in the composites ranged from 2.1 to 24.8 wt % and was found in the form of Tin. The structure of the Si₃N₄ matrices varied from amorphous (initially) to the- and-type, with increasingT _dep. Most of the- and-type deposits had a preferred orientation (001) parallel to the deposition surface. While the deposition surface of the amorphous deposits showed a pebble structure, the surfaces of the- and-type deposits were composed of various kinds of facets. The heat-treating experiment suggested that-Si₃N₄ obtained in the present work was formed directly via a vapour phase, and not from crystallization of amorphous Si₃N₄ or from transformation of-Si₃N₄.     

Si3N4／SiC纳米复合陶瓷的微观结构

利用ＪＥＭ２０００ＥＸⅡ高分辨电镜和ＨＦ２０００冷场发射枪透射电镜对Ｓｉ３Ｎ４ＳｉＣ纳米笔合陶瓷材料的微观组织，结构和成分进行了研究。结果表明，ＳｉＣ颗粒弥散分布基体相β－Ｓｉ３Ｎ４晶内和晶界，晶内ＳｉＣ颗粒与基体相的界面结构有三种类型；１）直接结合的的界面；２）完全非晶态的界面；３）混合型的界面，晶间ＳｉＣ颗粒与基体相的界面大部分是直接结合的。     

无压浸渗制备梯度Si3N4/Al复合材料

采用Al-Mg合金无压渗入具有梯度孔隙分布的Si3N4多孔预制体,制得大尺寸、梯度Si3N4/Al复合材料;对复合材料的显微组织,相组成,硬度进行了观察和测定,分析了层间铝合金薄层在释放梯度层间应力的作用,并采用SHPB装置对梯度复合材料进行动态压缩试验.试验结果表明梯度复合材料层间结合紧密,硬度从HRA80.5逐层过渡到HRA61.5,主要组成相为Al,Si3N4,AlN和Mg2Si;梯度复合材料在动态压缩过程中表现出较高韧性.     

Fracture toughness of Si3N4 and its Si3N4 whisker composite without sintering aids

Si₃N₄ without sintering aids is studied with special interest to the fracture behaviour and its relation to microstructure. Cracks propagated almost transgranularly and no rising R-curve behaviour was found, because crack-wake region gave no contribution on toughening due to very high grain-boundary bonding strength. Microstructure with highly elongated grains was obtained by addition of 20%Si₃N₄ whisker, but fracture toughness was found to be similar to that of the monolithic Si₃IM₄ with equiaxed grains. It is recognized that fracture toughness is not determined simply by apparent microstructural parameters such as mean aspect ratio of grains when grain-boundary bonding is sufficiently strong. Detailed examination of microfracture behaviour is, therefore, necessary for the analysis of toughening in this kind of composites.     

PECVD SiO2/Si3N4双层膜驻极体性能

本文研究了在带有Cr/Au电极的玻璃衬底上利用PECVD制备的SiO2/Si3N4双层膜驻极体性能.针对这种驻极体提出了一个简单的工艺流程暴露出一部分金属电极,并在电晕注极过程中将底电极引出接地.通过实验改变电晕注极过程中的注极时间、温度等因素,希望得到对PECVD制备的SiO2/Si3N4双层膜驻极体性能的优化.本文证实了PECVD双层膜具备良好的驻极体性能,有望广泛应用于微器件中.     

High temperature evaporation characteristics of amorphous Si3N4-C composite prepared by chemical vapour deposition

Evaporation characteristics of amorphous Si₃N₄ and amorphous Si₃N₄-C composite (6 wt % C) prepared by the chemical vapour deposition (CVD) were investigated in the temperature range of 1400 to 1650°C in a vacuum of about 10^?6 torr. The weight loss due to the evaporation was linear with time for all the samples tested. Evaporation rate of the amorphous CVD-(Si₃N₄-C) composite was 50 to 70% of that for the amorphous CVD-Si₃ N4. The activation energy for evaporation, calculated from the temperature dependence of the evaporation rates, was about 160 kcal mol^?1 for both samples. The carbon dispersed in the amorphous CVD-(Si₃N₄-C) composite reacted at the time of heat-treatment with the amorphous Si₃N₄ matrix and formedβ-SiC particles. Theβ-SiC particles were found to be about 100 nm in diameter and connected each other to form a three-dimensional network structure.     

Mechanical Properties and Microstructure of Si3N4-TiC Nanocomposites

1. IntroductionSilicon nitride is one of the promising structural ma-terials for high-temperature applications because of itshigh resistance to thermal shock, as well as high strength,high fracture toughness, and high resistance to chemicalattack[1~3]. However, wider application has been lim-ited mainly due to its inherent brittleness. Many effortshave been made to improve its properties by control-ling the microstructure or by fabricating various typesof composites[4~7].The silicon nitride wi…     

Microstructure and Toughness of Seeded Hot-Pressed Si3N4 Ceramics

Densification, phase transformation and fracture toughness were studied in hot-pressed Si_3N_4 seeded by in-houseproduced large, elongated β-Si_3N_4 seeds. A mixture of Y_2O_3-Al_2O_3 was used as the sintering aid. Concentration ofseeds were varied from 0 to 6 wt pct and the sintering time at 1700℃ was varied from 1 to 4 h. Maximum fracturetoughness of 9.0 MPam~(1/2) was measured in samples containing 5 wt pct seeds, hot pressed at 1700℃ for 4 h.     

凝胶注模Si3N4陶瓷的力学性能与显微结构

凝胶注模成型工艺是一种重要的原位凝固成型技术,它能有效地提高材料的可靠性以及降低复杂形状陶瓷部件的制造成本。本工作在Si     

烧结助剂对Si3N4/BN层状复合陶瓷结构与性能的影响

研究了MgO-Y₂O₃-Al₂O₃体系(相应的层状复合陶瓷试样记为A)、Y₂O₃-Al₂O₃体系(相应的层状复合陶瓷试样记为B)及La₂O₃-Y₂O₃-Al₂O₃体系(相应的层状复合陶瓷试样记为C)烧结助剂对Si₃N₄/BN层状复合陶瓷结构与性能的影响.研究表明:在相同的烧结工艺下,试样A、B、C的抗弯强度分别为700、630、610MPa,断裂功分别为2100、1600、3100J/m².试样A、B以脆性断裂为主,裂纹偏转现象不明显,而试样C的载荷-位移曲线显示了明显的“伪塑性”特征,裂纹的偏转与扩展现象明显.试样A中Si₃N₄晶粒大小不均且长径比较小,而试样C中长柱状Si₃N₄晶粒发育完善,有较大的长径比.     

用(CuZn)85 Ti15钎料连接Si3 N4陶瓷接头的微观结构

采用（CuZn)85Ti15钎料,研究了Si3N4陶瓷活性钎焊的接头微观组织结构,结果表明：在合适的钎爆条件下可以获得致密的Si3N4/Si3/N4接头,钎缝主要由含有Ti的硅化物和Ti的氮化物的Cu固溶体和Cu2TiZn组成,随着爆接温度从850℃升高,界面反应层增厚,填充金属中反应物的数量增多。尺寸增大,Zn能降低钎爆合金的熔化温度并降低钎焊温度,这有利于钎料的流动和润湿钎缝。Zn的蒸发将随着钎焊温度的上升而加剧,但它可以被合适的钎爆过程所控制。     

Processing and microstructural development of reaction-bonded sintering of a Si3N4/intermetallic composite

This paper focuses on the reaction-bonded sintering of a Si₃N₄/intermetallic composite. The preparation process and the microstructural characterization of this composite with different initial contents of Ni₃Al have been investigated. The effects of Ni₃Al addition on the nitridation of silicon and the phase transformation of Si₃N₄ formed, as well as the densification of the composite, also have been discussed. The addition of Ni₃Al particles accelerates the nitriding rate of silicon and results in the formation of -Si₃N₄ phase at low temperature due to the reaction occurring between silicon and Ni₃Al. Consequently, a completely nitrided and denser composite, compared with reaction-bonded sintered Si₃N₄, was obtained at low temperature. For comparison, pure silicon simultaneously processed was also investigated.     

The microstructural characterization of in situ grown Si3N4 whisker-reinforced barium aluminum silicate ceramic matrix composite

The microstructure of Barium Aluminum Silicate (BAS)/Silicon Nitride in situ whisker reinforced ceramic matrix composite was examined by X-ray diffraction, transmission electron microscopy, electron diffraction and energy-dispersive X-ray microanalysis. Although we cannot conclusively exclude the presence of orthorhombic BAS, hexagonal BAS and both -Si₃N₄ and -Si₃N₄ were identified in this material. The crystallization process of the glass phase can be taken almost to completion but a small proportion of residual glass phase is present. Both whiskerlike and equiaxed -Si₃N₄ exist in this material.     

Microstructure,chemical reaction and mechanical properties of TiC/Si3N4 and TiN-coated TiC/Si3N4 composites

Silicon nitride containing various compositions of as-received TiC and TiN-coated TiC, were hot pressed at 1800 °C for 1 h in a nitrogen atmosphere. In TiN-coated TiC/Si₃N₄ composites, TiC reacted first with the TiN coating to form a titanium carbonitride interlayer at 1450 °C, which essentially reduced further reactions between TiC and Si₃N₄ and enhanced densification. TiN-coated TiC/Si₃N₄ composites exhibited better densification, hardness, flexural strength and fracture toughness than those of as-received TiC/Si₃N₄. The toughening mechanisms for as-received TiC/Si₃N₄ and TiN-coated TiC/Si₃N₄ composite were attributed to crack deflection, load transfer and crack impedence by the compressive thermal residual stress.     

Strength,toughness and R-curve behaviour of SiC whisker-reinforced composite Si3N4 with reference to monolithic Si3N4

The flexural strength and fracture toughness of 30 vol% SiC whisker-reinforced Si₃N₄ material were determined as a function of temperature from 25 to 1400°C in an air environment. It was found that both strength and toughness of the composite material were almost the same as those of the monolithic counterpart. The room-temperature strength was retained up to 1100°C; however, appreciable strength degradation started at 1200°C and reached a maximum at 1400°C due to stable crack growth. In contrast, the fracture toughness of the two materials was independent of temperature with an average value of 5.66 MPam^1/2. It was also observed that the composite material exhibited no rising R-curve behaviour at room temperature, as was the case for the monolithic material. These results indicate that SiC whisker addition to the Si₃N₄ matrix did not provide any favourable effects on strength, toughness and R-curve behaviour.     

氮化硅晶须的研究现状

介绍了晶须的生长机理、氮化硅晶须的制备方法以及影响其生长的因素。阐述了氮化硅晶须增强复合材料的现状,指出加强晶须的基础研究,改进制备技术和降低成本是今后的发展方向。