立体光固化3D打印成型碳化硅陶瓷的烧结特性

立体光固化(SLA)作为碳化硅陶瓷材料3D打印的主流方法之一,具有广泛的应用前景。本文针对立体光固化成型的碳化硅素坯,进行了脱脂与反应熔渗试验,通过烧结过程中密度、强度、收缩率、微观结构的变化,研究了立体光固化成型碳化硅素坯的烧结特性。结果表明:脱脂后样品具有较低的烧结收缩率,特别是增材方向,为0.88%,脱脂后的坯体强度为0.26 MPa;光敏(UV)树脂的残留热解碳(PyC)呈网状结构连接碳化硅颗粒,热解碳局部出现断裂,同时样品沿打印层间出现微裂纹;反应熔渗后残留热解碳与硅反应生成β-SiC,连续相硅填充孔隙与层间微裂纹,样品体积密度为2.79 g/cm³,抗弯强度为183.99 MPa。     

熔融渗硅对石墨氧化行为的影响

分别在500 ℃、700 ℃、900 ℃及1 100 ℃空气条件下,对石墨及渗硅石墨进行氧化实验,以分析熔融渗硅对等静压石墨氧化行为的影响。采用扫描电镜(SEM)分析了样品表面及内部形貌,通过压汞法表征了样品的孔隙结构,并对材料的力学性能进行了测试分析。结果表明:500 ℃条件下,石墨和渗硅石墨均未发生明显的氧化失重现象;温度为700 ℃时,石墨的氧化失重率随时间延长明显增加,而该温度下渗硅石墨的氧化失重率变化较小。而且,渗硅石墨在700 ℃时仍能保持较好的强度,而此温度下,石墨随氧化时间的延长,强度明显降低,甚至被氧化成粉末状。因此,熔融渗硅在提高材料抗氧化性能的同时能够显著提升材料的强度。     

层压成型工艺制备近净成型反应烧结碳化硅材料的研究

采用层压成型工艺制备反应烧结碳化硅,其主要工艺步骤包括原材料料片的制备、层压成型、炭化及熔渗四步。材料在热压、炭化及熔渗后尺寸变化率分别为1.13%、1.65%与0.70%。碳化后得到的多孔体具有均匀的孔径分布,其中值孔径为0.23μm。制备的反应烧结碳化硅材料弯曲强度为269±23 MPa,弯曲模量为231±9 GPa,密度为3.016±0.003g/cm3,孔隙率为2.05±0.38%,实现了近净成型法制备高强度反应烧结碳化硅材料。     

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。     

一种硅基石墨密封用浸渍剂的制备研究

本文针对石墨材料多孔、结构不致密、气孔率较高、机械强度低的缺点,设计制备了无机硅基浸渗剂,以降低石墨材料的开孔率。实验结果表明浸渗剂的最佳配方工艺为:硅酸钠70g、四硼酸钠30g、分散剂14g、表面活性剂10g。使用该浸渗剂对石墨材料进行浸渗后,其开孔率由20.01降低到了12.88%,开孔率降低率为35.63%。     

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。     

反应熔渗烧结法制备MoSi2/SiC复合材料

采用反应熔渗烧结方法制备了弯曲强度达262 MPa的MoSi2／SiC复相材料，并研究了其烧结过程和烧结机理。结果表明：MoSi2／C坯体中熔渗硅的方法制备MoSi2／SiC复相材料，液态硅自然浸渗过程在1450℃即可完成，而且在该温度下液态硅的浸渗速率大于或等于反应速率。在1750℃时虽然C Si→β-SiC反应全部完成，但生成的β-SiC发生再结晶，使复相材料的强度降低。成型压力对反应浸渗材料的强度影响不大。     

渗硅碳化硅材料结构与性能关系的研究

采用低廉石油焦碳分为原料制造全碳粉生坯，通过有机添加剂来调配生坯中碳的比例，以控制烧结体中游离硅（fsi）、游离碳（fC）含量（其中fs,fc为烧结中未反应的硅和碳），研究了全碳粉反应硅碳化硅（PCRSC）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、游了碳含量对抗弯强度的影响。结果表明：渗硅碳化硅材料中随游离硅含量的增加，其抗弯速度下降，并且二者呈直线关系，符合线性复合规则，另一方面，游离碳含量较高的渗硅碳化硅材料，尽管游离硅含量低，但其抗弯强度低于等量或较多游了硅含量的渗硅碳化硅材料的抗弯强度。     

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。     

改性膨胀性石墨对硬质聚氨酯泡沫性能和胞体结构的影响

以改性膨胀性石墨和膨胀性石墨为添加剂制备复合聚氨酯泡沫材料,并表征了微观结构、表观密度、压缩性能、保温性能等。改性膨胀性石墨和膨胀性石墨物对材料的微观结构有很大的影响。加入改性膨胀性石墨可以有效提高材料的压缩模量,其压缩模量为143.58MPa,而膨胀性石墨的添加会降低材料的压缩模量,其压缩模量为106.62MPa,而没有添加膨胀性石墨的样品的压缩模量为为108.53MPa。改性膨胀性石墨和膨胀性石墨都可以提高材料的阻燃性能。     

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.     

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.     

Graphite-Si-SiC ceramics produced by microwave assisted reactive melt infiltration

A novel microstructure of graphite-Si-SiC ceramics was successfully prepared by liquid silicon infiltration of graphite-based preforms; instead of using conventional methods, the reactive infiltration process was assisted by microwaves. The effects of microwave power variation on the microstructure and the mechanical properties of infiltrated materials were studied. X-ray diffraction and Raman investigations showed the presence of both unreacted graphite and Si in addition to SiC formed at their interface. The graphitic and silicon phases were separated by a SiC network, which results more homogeneous as microwave power was increased. The amount of SiC was found to be higher in function of the growing power level; a higher conversion of graphite into SiC yielded a more dense material. The bending strength measurements confirm this, showing higher values for the samples processed using a power level of 75% of the full power compared to those obtained with 30% and 60%.     

Thermo-mechanical characterization of carbon fiber reinforced silicon carbide composites having boron nitride as an interphase material

The carbon fiber reinforced silicon carbide composites were prepared by an isothermal chemical vapour infiltration process. In order to achieve the required density, the carbon fiber preforms in the form of rectangular panels were infiltrated by silicon carbide (SiC) matrix. Prior to the matrix infiltration, a thin coating of boron nitride, as an interphase, was applied on the fiber preform. The test samples were subjected to seal coating of silicon carbide by chemical vapour deposition process. The effect of protective SiC seal coating was examined by testing (3-point bend test) the uncoated and the seal coated samples at different temperatures. Higher value of the flexural strength was observed for the seal coated samples as compared to the uncoated samples, when got tested at high temperature (up to 1400?°C). The detailed analysis of the fractured surfaces of the tested samples was carried out.     

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.     

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。     

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.