渗硅碳化硅材料的研究

本文通过调整生坯结构,研究了全碳粉渗硅碳化硅（PCRBSC0的显微结构及力学性能。实验结果表明：生坯结构影响烧结体显微结构,同时显微结构、游离硅含量影响材料力学性能,渗硅碳化硅（PCRBSC0材料中随游离硅含量的增加,其抗折强度下降,并且二者呈直线关系,符合线性复合规则：P＝∑i=1^nPiVi。     

碳化硅材料中游离硅及游离碳对性能的影响

研究了全碳粉反应渗硅碳化硅（PCRBSC）材料的结构与力学性能的关系。分析了渗硅碳化硅材料中游离硅（fsi),游离碳（fc)含量对抗折强度的影响。结果表明：参硅碳化硅材料中随游离硅（fsi)含量的增加,其抗折强度下降,并且二者呈直线关系,符合线性复合规划,另一方面,游离碳（fc)含量较高的渗硅碳化硅材料,尽管游离硅（fsi)含量低,但其抗折强度低于等量或较多游离硅（fsi)含量的渗硅碳化硅材料的抗折强度。     

高温处理对渗硅碳化硅性能的影响

研究了全碳粉反应渗硅碳化硅（PCRBSC）材料在1700℃高温氩气氛中4h的处理，研究结果表明，RCPBSC材料的结构对高温处理后的强度有很大的影响，特别是游离硅sfi，游离碳fc的含量明显影响高温处理后PCRBSC材料的抗折强度。     

高温处理对渗硅碳化硅性能的影响

研究了全碳粉反应渗硅碳化硅（ＰＣＲＢＳＣ）材料在１７００℃高温氩气氛中４ｈ的处理,研究结果表明：ＰＣＲＢＳＣ材料的结构对高温处理后的强度有很大的影响,特别是游离硅ｆｓｉ、游离碳ｆｃ的含量明显影响高温处理后ＰＣＲＢＳＣ材料的抗折强度。     

渗硅碳化硅材料的高温氧化

研究了全碳粉反应渗硅碳化硅(PCRBSC)材料,在1300℃静态空气中的高温氧化行为.研究结果表明:PCRBSC材料的氧化过程遵循直线-抛物线规律,其结构对高温氧化有很大的影响,特别是游离硅fsi和游离碳fc的含量对氧化影响更大,fsi含量高的PCRBSC材料单位面积氧化增重(Δm/s)明显,fc含量高的PCRBSC材料氧化后表现为先减重后增重,氧化层断口经扫描电镜观察有明显的气孔存在.     

碳化硅晶须改性反应烧结碳化硅陶瓷的显微结构及性能

以碳化硅晶须为增强体、碳化硅--碳为基体制备晶须增强反应烧结碳化硅复合材料,研究了碳化硅晶须、碳含量对复合材料显微结构与性能的影响。结果表明:碳化硅晶须经高温反应烧结后仍保持表面的竹节结构,且晶须增强体与反应烧结碳化硅基体间形成适中的界面结合强度;材料断口处有明显的晶须拔出,当碳黑含量为6%(质量分数)时,随着晶须含量的增加,材料的抗弯强度从200MPa提高到310MPa(晶须含量15%),当碳黑含量为18%时,随着晶须含量的增加,材料断裂韧性从3.3MPa·m1/2提高到4.3MPa·m1/2;碳化硅晶须含量过高时,晶须的"搭桥"效应导致材料中含有较多的游离硅,限制了材料力学性能进一步提高;微氧化处理使材料表面形成致密、均匀的氧化膜,可显著提高反应烧结碳化硅的抗弯强度和断裂韧性。     

反应烧结碳化硅高温性能的研究进展

反应烧结碳化硅具有优良的力学性能、抗侵蚀性能和抗氧化性能等优点,是一种高致密度、低成本和净尺寸成型的材料.但由于反应烧结法的特殊工艺,反应烧结碳化硅中常含有较多游离硅,严重损害了材料的高温性能.主要阐述了反应烧结碳化硅高温力学性能、抗氧化性能、导热性能和抗热震性能的研究现状,并总结了近年来降低游离硅含量、提高反应烧结碳...     

专利信息

纯碳粉水基分散一步法制造反应烧结碳化硅陶瓷材料的方法一种用水为分散剂,以纯碳粉取代碳化硅粉制造高性能反应烧结碳化硅陶瓷的方法,采用添加外加剂的方法制成高分散的水基泥浆(料),采用注浆、挤塑、凝胶注成型的方法制成生坯,用控制粉料粒径以及烧蚀剂、填充剂加入量的方法,调整生(素)坯的孔径分布和单位体积碳含量,生坯经干燥后,经1550～1650℃真空下或1850～2050℃氩气气氛下渗硅烧结2h,制得反应烧结碳化硅陶瓷材料。一种泡沫剂及其制备方法本发明公开了一种泡沫剂及其制备方法,其主要组成及含量为(重量百分比):骨胶1.55%～1.65%,松香3…     

碳化硅木质陶瓷的显微结构及力学性能

以汉麻秆芯碳化后的碳粉为原料,分别采用注浆和干压成型工艺制备素坯,通过反应烧结制备出碳化硅木质陶瓷.研究了注浆成型工艺中悬浮稳定剂的种类和添加量对浆料性能的影响.采用激光共聚焦显微镜、扫描电子显微镜和X射线衍射仪等分析了碳化硅木质陶瓷的显微结构、物相组成及力学性能.结果表明:采用注浆成型制备的碳化硅木质陶瓷力学性能优异,实测的游离硅含量同理论计算结果一致,说明渗硅过程中硅碳反应充分,烧结体显微硬度、弯曲强度、弹性模量和断裂韧性分别为22.3 GPa、397 MPa、290 GPa和3.0 MPa·m1/2.     

硅/碳化硅材料显微特征与强度关系研究

通过改变坯体碳/碳化硅质量比,采用反应烧结方法制备了不同硅相含量和次生碳化硅分布形式的硅/碳化硅复合材料。探讨了该复合材料不同显微组织的形成机理。用三点弯曲法评价了材料强度与显微组织的关系,结合断口断裂模式,从热失配引起颗粒周围残余应力和界面能两个方面对强度-组织之间的关系进行了定性讨论。结果表明,硅/碳化硅相体积含量、碳化硅分布形态、热失配导致的残余应力是影响材料强度的主要因素,优化制备工艺参数是获得高性能材料的关键。     

纳米SiO2对先驱体浸渍裂解法制备SiCf/SiC复合材料力学性能的影响

以纳米SiO2为填料,采用先驱体浸渍裂解法制备2.5D-SiCf/SiC（D为维数,SiCf为SiC纤维）复合材料,研究了前驱液中纳米SiO2含量对复合材料力学性能的影响。结果表明,纳米SiO2的添加能有效抑制先驱体裂解过程中的体积收缩,提高致密度,但过量引入易导致浸渍液黏度过高,浸渍效率降低。纳米SiO2含量对材料力学性能有较大影响,添加纳米SiO2后材料的抗弯强度和断裂韧性均高于没有添加的样品,材料抗弯强度随纳米SiO2含量的增加先增大后降低。当浸渍液中纳米SiO2含量为6%时,复合材料具有优异的力学性能,抗弯强度达到211.1MPa。     

不同铝源对SiC/堇青石复相多孔陶瓷的制备及性能影响

以碳化硅、氮化铝、层析氧化铝、氢氧化铝、氟化铝、滑石为主要原料,石墨为造孔剂通过原位反应烧结技术制备碳化硅/堇青石复相多孔陶瓷.研究了含铝化合物种类、烧结温度、石墨含量对SiC/堇青石复相多孔陶瓷相组成、微观结构、气孔率和抗折强度的影响,同时对S0组在1200℃烧结温度下制得的SiC/堇青石复合多孔陶瓷的孔径分布进行了测试分析.结果表明:以AlN为铝源在1200℃下烧结,石墨含量在15％时,堇青石结合SiC多孔陶瓷的抗弯强度和气孔率两项综合性能达到最优,气孔率为31.99％,相应的弯曲强度86.20 MPa.S0组的平均孔径大小在3.0191 μm.     

Preparation of reaction bonded silicon carbide (RBSC) using boron carbide as an alternative source of carbon

RBSC composites are fully dense materials fabricated by infiltration of compacted mixtures of silicon carbide and carbon by molten silicon. Free carbon is usually added in the form of an organic resin that undergoes subsequent pyrolysis. The environmentally unfriendly pyrolysis process and the presence of residual silicon are serious drawbacks of this process. The study describes an alternative approach that minimizes the residual silicon fraction by making use of a multimodal particle size distribution, in order to increase the green density of the preforms prior infiltration. The addition of boron carbide provides an alternative source of carbon, thereby eliminating the need for pyrolized organic compounds. The residual silicon fraction in the RBSC composites, prepared according to the novel processing route, is significantly reduced. Their mechanical properties, in particular the specific flexural strength is by 15% higher than the value reported for RBSC composites prepared by the conventional approach.     

Effect of carbon particle and carbon fiber on the microstructure and mechanical properties of short fiber reinforced reaction bonded silicon carbide composite

Variation of microstructure and mechanical behavior was investigated with the content increase of carbon particles and carbon fiber in the reaction bonded silicon carbide composites. The composites were prepared by slip casting and liquid silicon infiltration. The bulk density is raised with the increase of carbon black due to the formation of fine β-SiC particles. The flexural strength increases for the reduction of residual Si and the formation of SiC framework; whereas a very high carbon content reduces the flexural strength. The fracture toughness is controlled by the contents of carbon particle and carbon fiber. Thus, fiber debonding, fiber pullout and crack deflection are considered as the main toughening mechanisms. Annealing treatment can effectively improve both the flexural strength and fracture toughness. An increase by 49% of fracture toughness is obtained. A series of structural models are proposed to illustrate the structure changes of carbon fiber.     

C/C多孔体对C/C-SiC复合材料微观结构和弯曲性能的影响

以4种纤维含量相同(32%,体积分数,下同),用化学气相渗透(chemical vapor infiltration,CVI)法制备了4种密度的碳纤维增强碳(carbon fiber reinforced carbon,C/C)多孔体,基体炭含量约20%～50%.利用液相渗硅法(liquid silicon infiltration,LSI)制备了C/C-SiC复合材料,研究了C/C多孔体对所制备的C/C-SiC复合材料微观结构和弯曲性能的影响.结果表明:不同密度的C/C多孔体反应渗硅后,复合材料的物相组成均为SiC,C及单质Si;随着C/C多孔体中基体炭含量的增加,C/C-SiC复合材料中SiC含量逐渐减少而热解炭含量逐渐增加.C/C-SiC复合材料弯曲强度随着材料中残留热解炭含量增加而逐渐增加,热解炭含量为约42%的C/C多孔体所制备的C/C-SiC复合材料的弯曲强度最大,达到320 MPa.     

Preparation of low residual silicon content Si-SiC ceramics by binder jetting additive manufacturing and liquid silicon infiltration

Complex silicon carbide (SiC) ceramic components are difficult to fabricate due to their strong covalent bonds. Binder jetting (BJ) additive manufacturing has the outstanding advantages of high forming efficiency and no thermal deformation, especially suitable for printing complex structure SiC components. This study tried to obtain low silicon content silicon carbide ceramics by binder jetting followed by phenolic resin impregnation and pyrolysis (PRIP) and liquid silicon infiltration (LSI). BJ was used for the SiC green parts fabrication, and the highest compressive strength (7.7 ± 0.3 MPa) and lowest dimensional deviations (1.2–1.6 mm) were obtained with the printing layer thickness of 0.15 mm. Subsequently, PRIP treatments were introduced to increase the carbon content for the following LSI process. As the number of PRIP cycles increased, the carbon density of SiC/C preform increased and the porosity decreased. After the LSI treatment, the final Si-SiC composites processed with 2 PIRP cycles reached the highest flexural strength (257 ± 14.26 MPa) and the best wear resistance. This was attributed to the low residual silicon content (10.2 vol%) and almost no residual carbon. Furthermore, several complex structural components were fabricated using these methods. The preparation of complex components verifies the feasibility of BJ and LSI for manufacturing high-strength and high-precision SiC ceramics. Besides, this work hopes to provide technical guidance for the preparation of complex SiC composites in the future.     

Combination of direct ink writing and reaction bonded for rapid fabrication of SiCw/SiC composites

Silicon carbide ceramic matrix composites are widely used in aerospace field due to their advantages of high temperature resistance, high strength and corrosion resistance. However, its application is greatly limited because of the difficulty in preparing complex shape structures by traditional machining methods. Here, a new strategy for preparing SiC_w/SiC complex structure by combining direct ink writing with reaction bonding is proposed. A water-based slurry consisting of silicon carbide, carbon powder and silicon carbide whisker was developed. The influence laws of C content and SiC_w content in slurry on sintering properties of direct-written samples were studied. The reaction bonding mechanism and whisker reinforcing and toughening mechanism were analyzed by means of microstructure and phase composition. The results show that the slurry exhibits shear thinning behavior with stress yield point, and its flow behavior and plasticity meet the requirements of direct writing. When the carbon content is 6.4 wt%, the maximum flexural strength is 239.3 MPa. When 15 wt% SiC_w was added, the flexural strength of the composite reached 301.6 MPa, and when 20 wt% SiC_w was added, the fracture toughness of the composite reached 4.02 MPa m^1/2, which was increased by 26% and 18% compared with single-phase SiC, respectively. The reinforcing and toughening mechanisms of the whiskers mainly include whisker pullout, crack deflection and whisker bridging. After direct ink writing and reaction bonded, the whole process shows good near net forming ability. 3D printed SiC_w/SiC composites have great application prospects in aerospace field.     

Robocasting of reaction bonded silicon carbide structures

A novel shaping method for the fabrication of reaction bonded silicon carbide structures was investigated in this work. A paste consisting of silicon carbide as inert filler and carbon powder was developed and printed by robocasting technology. Layer by layer deposition of the ceramic paste facilitates the printing of complex shaped structures. Different structures such as lattices, hollow cylinders, bending bars and gyroids were printed using nozzles with diameter of 0.5 mm and 1.5 mm. After pyrolysis at 700 °C and further heat treatment at 1850 °C the samples were infiltrated using the liquid silicon infiltration technique to obtain dense near-net shape RBSC structures. The robocasted structures showed a hardness of approximately 20 GPa, a thermal conductivity of ～112 W/m*K, Young’s modulus of ～356 GPa, flexural strength of ～224 MPa and an amount of residual silicon of approximately 23%. These measured properties are comparable with those of traditionally fabricated RBSC.     

Processing and fracture behaviour of hot pressed silicon carbide whisker reinforced alumina

The improvement of mechanical properties of silicon carbide whisker reinforced alumina has been investigated with emphasis on the effects of the whisker type and content, the hot pressing temperature and the influence of an interfacial film between the whisker and the matrix. The introduction of silicon carbide whiskers significantly improves the fracture toughness, flexural strength and creep resistance of polycrystalline alumina.

However, these properties are strongly dependent on the size and morphology of whiskers. Large diameter whiskers generate extensive micro-cracking which leads to a decrease in flexural strength. Also, the presence of carbon-coated SiC whiskers substantially increases the high temperature strain rate by promoting cavitation. A grain boundary glassy phase introduced by the carbon coating was also detected.