SiC陶瓷／SiC陶瓷及SiC陶瓷／Ni基高温合金SHS焊接中的界面反应及 …

采用加压自蔓延高温合成（ＳＨＳ）焊接工艺,连接ＳｉＣ陶瓷／ＳｉＣ陶瓷以及ＳｉＣ民／Ｎｉ基高温合金,为了得到牢固的界面结合,实验了多种焊接配方,而且基于润湿性、亲合笥、ＳＨＳ起爆温度及界面反应的可能性等多方面的考虑,设计并实验了多层焊料配方、微观结构显示,液相反应产物对ＳｉＣ陶瓷的润湿性很好,液相能够渗入陶瓷的表面开孔之中,而且界面结合很好,成分分析证实,界面处发生了界面扩散,这有助于界面结合强度的     

高温等静压后处理液相烧结SiC陶瓷的强化与增韧机理

研究了高温等静压（ＨＩＰ）后处理对液相烧结ＳｉＣ陶瓷的强化与增韧机理。通过讨论ＨＩＰ后处理对材料显微结构与力学性能的影响,建立了实验模型,深入分析了ＨＩＰ氮化后处理通过中,起主导作用的物理化学过程,并将此过程分为Ｎ２的扩散、表面氮化反应及进一步的致密化三个阶段。结果表明,ＨＩＰ后处理通过受液相烧结ＳｉＣ陶瓷显微结构的影响非常显著,当ＳｉＣ的液相烧结温度较低,晶粒尺寸较小时,将有利于Ｎ２沿ＳｉＣ晶界     

AIN在SiC—AIN—Y2O3复相陶瓷中的作用

氮化铝相在ＳｉＣ－ＡＩＮ－Ｙ２Ｏ３复相陶瓷中起着至关重要的作用。在２０５０℃高温时，ＡＩＮ颗粒表面发生固相蒸发现象，并聚集到ＳｉＣ颗粒周围最终形成固溶体，改善了ＳｉＣ颗粒周围最终形成固溶体，改善了ＳｉＣ陶瓷的晶界结构，使该复相材料具有良好的机械性能，其室温抗折强度为６１０ＭＰａ，这一强度可持续至１４００℃高温，断裂韧性达到８．１ＭＰａ．ｍ＾１／２。     

液相烧结SiC陶瓷

采用Ｙ２Ｏ３,Ａｌ２Ｏ３为烧结助剂,研究了烧结助剂的含量及组成对ＳｉＣ陶瓷的烧结性和力学性能的影响。结果表明,Ｙ２Ｏ３,Ａｌ２Ｏ３原位形成了ＹＡＧ,材料以液相烧结机制致密化,与传统的固相烧结相比,液相烧结使ＳｉＣ陶瓷性能显著提高,在较佳条件下,材料强度和韧性分别达到７０７ＭＰａ,１０．７ＭＰａ·ｍ＾１／２,显微结构观察表明,裂纹偏转和微裂纹为主要的增韧机理,这与其弱的界面结合有关,而强度的提高则得     

Si3N4／纳米SiC复相陶瓷的研究

采用纳米ＳｉＣ粉体制备了Ｓｉ３Ｎ４／纳米ＳｉＣｐ复相陶瓷。研究了制备工艺、纳米ＳｉＣ含量对材料性能及显微结构的影响,并对材料显微结构特点与强韧化机制进行了分析 。结果表明：添加２０ｖｏ％〈１００ｎｍ的ＳｉＣ粉体时,复相陶瓷的室温抗弯强度达８５６ＭＰａ,当添加１０ｖｏ％上述ＳｉＣ粉体时,复相陶瓷的增韧效果最佳,断裂韧性达８．２７ＭＰａｍ＾１／２,比基体材料提高了２３％。     

陶瓷注射成型有机载体的选择及相容性研究

对数种陶瓷注射成型常用的有机载体，通过ＤＳＣ，ＳＥＭ，溶度参数计算和高温金相显微镜观察，定性和定量地研究了有机载体之间的相容性及它们与Ｓｉ３Ｎ４粉体的润湿性，在此基础上的考察了配方不同的注射成型混合物料的流变特性，确定了适于陶瓷注射成型的有机载体。     

增韧SiC陶瓷在蒸馏水润滑下的摩擦学特性

在ＭＭ－２００块－环接触磨损试验上，测定了一种增韧ＳｉＣ陶瓷在蒸馏水下自配对，与ＷＣ＋Ｃｏ硬质合金和等离子喷涂Ｃｒ２Ｏ３涂层配对摩擦系数和摩损系数，利用ＳＥＭ，ＸＰＳ和ＦＴＩＲ等测试技术，观察和分析了磨痕的形貌和化学组成，讨论了摩擦副材料的显微结构和机械性能对ＳｉＣ陶瓷的摩擦学的特性的影响，实验表明，该增韧ＳｉＣ陶瓷大水介质中滑动，ＳｉＣ与水发生化学反应，在磨损表面形成一层由ＳｉＯ２与Ｓｉ（ＯＨ）     

氮化硅陶瓷连接工艺及结合强度研究

采用由Ｙ２Ｏ３,Ａｌ２Ｏ３,ＳｉＯ２和Ｓｉ３Ｎ４粉料配制的焊料对氮化硅陶瓷进行连接试验,探讨了组分、焊接温度、压力和保温时间对结合强度的影响规律。结果表明,结合层致密化程度结合强度的关键因素。随着焊料中α－Ｓｉ３Ｎ４含量的增加,结合强度先升后降,在较高的温度下纯液态玻璃焊料容易从结合层流失,而对于氮化硅－玻璃复合焊料,高温加速了α－Ｓｉ３Ｎ４和βＳｉ３Ｎ４转变的动力。合适的压力可以保证焊料具有良好     

SiCw／涂层／TZP陶瓷复合材料界面化学键的XPS和IR研究

本文用ＸＰＳ和ＩＲ测定了ＳｉＣｗ／（Ａｌ２Ｏ３，莫来石）涂层／ＴＺＰ陶瓷复合材料的界面化学键。结果表明ＳｉＣｗ／Ａｌ２Ｏ３、莫来石、ＴＺＰ界面为化学结合而Ａｌ２Ｏ３、莫来石／ＴＺＰ界面为物理结合。     

化学气相渗（CVI）C／SiC复合材料性能控制

本研究用化学气相渗技术制备了四种Ｃ／ＳｉＣ复合材料：在ＣＨ３ＳｉＣｌ３＋Ｈ２（普通）＋Ａｒ（高纯）系统中制各了两种材料：材料Ａ为１Ｋ炭布层叠无热解炭界面层，材料Ｂ为１Ｋ炭布层叠有热解炭界面层；在ＣＨ３ＳｉＣｌ３＋Ｈ２（高纯）＋Ａｒ（高纯）系统中制备了另两种材料：材料Ｃ和材料Ｄ分别为１Ｋ、Ｔ３００炭布层叠有热解炭界面层．分别对其中每两种材料进行了相互比较，研究了骨架纤维、界面层及基体对整个复合材料性能的影响；通过控制上述三方面因素可以对Ｃ／ＳｉＣ复合材料的总体结构进行设计从而控制其材料最终性能。     

High-Temperature Chemical Stability of Plasma-Sprayed Ca05Sr05Zr4P6O24 Coatings on Nicalon/SiC Ceramic Matrix Composite and Ni-Based Superalloy Substrates

The potential application of Ca05Sr05Zr4P6O24 (CS50) as a corrosion-resistant coating material for Si-based ceramics and as a thermal barrier coating material for Ni-based superalloys was explored. A ∼200 (xm thick CS50 coating was prepared by air plasma spray with commercially available powder. A Nicalon/SiC ceramic matrix composite and a Ni-based superalloy coated with a ∼200 (xm thick metallic bond coat layer were used as substrate materials. Both the powder and coating contained ZrP2O7 as an impurity phase, and the coating was highly porous as-deposited. The coating deposited on the Nicalon/SiC substrate was chemically stable upon exposure to air and Na2SO4/O2 atmospheres at 1000°C for 100 h. In contrast, the coating sprayed onto the superalloy substrate significantly reacted with the bond coat surface after similar oxidation in air.     

硅液相浸渍反应制备TiC/SiC和TiN/SiC复相陶瓷

以滤纸、酚醛树脂和氧化钛为原料,经过模压成型、固化、碳化及不同条件下渗硅制备了TiC/SiC和TiN/SiC复相陶瓷。通过X射线衍射和扫描电子显微镜研究了TiC/SiC和TiN/SiC复相陶瓷的微观结构和物相组成,测量了复相陶瓷的弯曲强度和断裂韧性。结果表明:真空条件下液态渗硅获得的TiC/SiC复相陶瓷具有多孔的微观结构,其弯曲强度和断裂韧性较小。氮气气氛下液态渗硅制备的TiN/SiC复相陶瓷结构致密,有较高的弯曲强度和断裂韧性。不同反应生成的TiC,TiN陶瓷颗粒对液态硅的润湿性不同,使得生成的复相陶瓷具有不同的微观结构。TiN/SiC复相陶瓷中TiN颗粒的引入,在基体与第二相颗粒间的界面上产生拉应力和压应力,使达到这一区域的裂纹偏转,从而获得增韧效果。     

A novel high entropy CoFeCrNiCu alloy filler to braze SiC ceramics

In order to reduce intermetallic compound formations in brazed joints, a CoFeCrNiCu high entropy alloy was invented and employed to braze SiC ceramics. Results show that SiC ceramics were tightly and strongly brazed with the CoFeCrNiCu filler. Microstructure, phase and shear strength were systematically studied for joints brazed at different temperature. Main compositions were identified as high-entropy FCC, Cu(s, s), Si(s, s), and Cr₂₃C₆ phases, regardless the brazing temperature differences. After being brazed at 1453 K, the joint reached a maximum shear strength of 60 MPa, much higher than those brazed with conventional AgCuTi filler. Thanks to high entropy effect of CoFeCrNiCu filler, random solid solution turned out in the seam and benefitted joint quality. The successful use of CoFeCrNiCu high entropy alloy as fillers can expand the application range of high entropy alloys and provide a new filler system to braze ceramics.     

Interfacial microstructure and mechanical properties of SiC joints achieved by reactive air brazing using Ag-V2O5 filler

SiC ceramics are successfully brazed via reactive air brazing using Ag-V₂O₅ fillers. The wettability of SiC ceramics by Ag-V₂O₅ fillers is investigated. Interfacial microstructure of SiC joints is analyzed by scanning electron microscopy and transmission electron microscopy with energy dispersive spectroscopy. Effect of the brazing filler composition on the microstructure and mechanical properties of SiC joints is studied in detail. The V₂O₅ from the brazing fillers is found to react intensively with SiC, and the SiO₂ reaction layer with the thickness of ?7 μm is formed on the SiC surface which ensures a good wetting of the brazing filler on SiC ceramics. The brazing seam is composed of Ag and VO₂ with small amount of remaining V₂O₅. The maximum shear strength (?58 MPa) is achieved when using the optimized brazing process (Ag-8V₂O₅, 1050 ℃/30 min, the loading pressure is ?20 kPa and the cooling rate is 2 ℃/min).     

Design of a C/SiC functionally graded coating for the oxidation protection of C/C composites

To reduce the residual thermal stress between the carbon fiber-reinforced carbon (C/C) composites and the SiC coating layer, functionally graded materials (FGM) consisting of a C/SiC compositionally graded layer (C/SiC interlayer) were adopted. After designing the compositional distribution of the C/SiC interlayer which can relieve the thermal stress effectively, the deposition conditions of the entire compositional range of the C/SiC composites were determined using a thermodynamic calculation. According to the design and calculation the C/SiC interlayer and the SiC outer layer were deposited on the C/C composites by a low pressure chemical vapor deposition (LPCVD) method at deposition temperatures of 1100 and 1300 °C. The stress calculation and the experimental results suggested that the SiC-rich compositional profile in the FGM layer is the most effective for relieving the thermal stress and increasing the oxidation resistance.     

Processing and characterization of particles reinforced SiOC composites via pyrolysis of polysiloxane with SiC or/and Al fillers

Polysiloxane loaded with SiC as inert filler, and Al as active filler, was pyrolyzed in nitrogen to fabricate SiOC composites, and the processing and properties of the filled SiOC composites were investigated. Adding SiC fillers could reduce the linear shrinkage of filler-free cured polysiloxane in order to obtain monolithic SiC/SiOC composites. The flexural strength of SiC/SiOC composites reached 201.3 MPa at a SiC filler content of 27.6 vol.%. However, SiC/SiOC composites exhibited poor oxidation resistance, thermal shock resistance and high temperature resistance. Al fillers could react with hydrocarbon generated during polysiloxane pyrolysis at 600 °C and N₂ at 800 °C to form Al₄C₃ and AlN, respectively. The volume expansions resulting from these two reactions were in favor of the reduction in linear shrinkage and the improvement in flexural strength of SiC/SiOC composites. The flexural strength of Al-containing SiC/SiOC composites was 1.36 times that of SiC/SiOC composites without Al at an Al filler content of 20 vol.%. The addition of Al fillers remarkably improved the high temperature resistance and oxidation resistance of SiC/SiOC composites, but not thermal shock resistance.     

多孔SiC陶瓷/石蜡复合相变材料定型封装及热性能研究

以微米级SiC粉为原料,采用冷冻干燥工艺制备具有连贯层状孔结构的SiC陶瓷。以多孔SiC陶瓷为基体,石蜡为相变芯材,通过真空浸渍法制备多孔SiC陶瓷/石蜡复合相变材料,研究了石蜡在层状多孔SiC陶瓷内的浸渗行为及复合材料的储热性能。结果表明,层片状多孔SiC陶瓷的显微形貌对石蜡的浸渗过程及储热性能有明显影响。当石蜡负载量为21.7%(质量分数)时,复合相变材料熔融温度为59.6 ℃,凝固温度为53.9 ℃,相变潜热为28.4 J/g,室温下的热导率为2.4 W·(m·K)^-1。复合相变材料吸热峰和放热峰强度随着石蜡负载量减少而降低,当温度为200 ℃时,多孔SiC陶瓷/石蜡复合相变材料失重为5%(质量分数),表明材料具有良好的热稳定性。复合相变材料在100 ℃热处理30 min后陶瓷基体未发生形变,经100次热循环后具有稳定的相变潜热和良好的定型能力。     

Brazing of SiC ceramics pretreated by chromium coating using inactive AgCu filler metal

In this work, chromium coating conducted by magnetron sputtering was introduced to braze SiC ceramics using inactive AgCu filler metal. The results showed that reliable metallurgical bonding of SiC ceramics was obtained at 900°C for 10 minutes. SEM, XRD, and TEM were used to identify the reaction phase in the joint, and the typical interfacial microstructure was SiC/mixed CrSi₂ + Cr₂₃C₆ layer/CrSi₂/Ag(s,s)+Cu(s,s)/CrSi₂/mixed CrSi₂ + Cr₂₃C₆ layer/SiC. The shear strength of SiC joint using chromium coating brazed with inactive AgCu filler metal was 29.6 MPa and the joint fractured at the SiC substrate entirely after shear test. The proposed active element coating method provides a feasible way to achieve the brazing of ceramics.     

Processing and properties of porous SiC ceramics prepared by yttrium aluminum garnet infiltration

Oxide bonded porous SiC ceramics were synthesized by infiltrating a liquid precursor of yttrium aluminum garnet into porous powder compact of SiC followed by sintering at 1300‐1500°C in air. Infiltration rate was estimated using weight gain by the liquid precursor sol into porous SiC powder compact as a function of time and was explained by Darcy's and Ficks's laws. The effects of SiC particle sizes and sintering temperatures on the formation of bonding phases, microstructure, SiC oxidation degree, flexural strength, porosity, and pore size distribution of porous SiC ceramics were studied. Various crystalline oxide phases were detected by XRD analysis. Depending on the starting SiC powder sizes and sintering temperatures, the porosity of the final ceramics varied nearly in the range of ~29‐41 vol. % with the variation of average pore diameter between ~5 and 30 μm. Flexural strength varied from 41 to 8 MPa depending on porosity. The effect of corrosion on oxide bond phases was investigated in strong acidic and basic medium at 90°C. The ceramics showed better corrosion resistance in acidic medium compared to basic medium. In basic medium, significant reduction in flexural strength (~42%) was arisen.     

多孔碳化硅陶瓷的原位氧化反应制备及其性能

以SiC为陶瓷骨料,Al2O3作为添加剂,通过原位氧化反应制备了Sic多孔陶瓷,并对其氧化反应特性及性能进行了研究.结果表明:在1 300～1 500℃,随烧结温度的升高,SiC的氧化程度增加,SiC多孔陶瓷的强度逐渐增加,但开口孔隙率有所降低.莫来石相在1 500℃开始生成·当烧结温度升高到1 550℃时,莫来石大量生成,得到了孔结构相互贯通且颈部发育良好的莫来石结合SiC多孔陶瓷;由于在SiC颗粒表面上覆盖了致密的莫来石层,SiC的氧化受到抑制,开口孔隙率因而升高,SiC多孔陶瓷的强度因莫来石的大量生成而增加.由平均粒径为5.0um的SiC,并添加20%(质量分数)Al2O3,经1 550℃烧结2h制备的SiC多孔陶瓷具有良好的性能,其抗弯强度为158.7MPa、开口孔隙率为27.7%.