真空热压烧结制备高性能B4C/Al复合材料

B4C/Al复合材料因其优异的性能,受到了人们广泛关注.以Al粉和B4C粉体为原料,采用真空热压烧结法,在高于Al熔点温度时,制备出了碳化硼含量10wt%的铝基复合材料.研究结果表明:烧结温度为700 ℃,烧结压力为30 MPa,保温时间为45 min时,获得的B4C/Al复合材料力学性能最佳,其相对密度为98.2%,硬度为2.53 GPa,抗弯强度为350 MPa.球磨混料使Al颗粒表面生成少量Al2O3,在烧结过程中,Al2O3与B2O3发生固-液反应形成共融物,改善了B4C/Al之间的界面结合强度,从而获得力学性能优异的B4C/Al复合材料.     

微波烧结WC-ZrO_2复合材料的微观组织及增韧机理

采用微波烧结工艺制备超细晶WC-ZrO_2复合材料,研究了其显微组织和力学性能。结果表明:ZrO_2含量为10 wt%、烧结温度为1360°C时获得的WC-10ZrO_2复合材料综合性能良好,致密度达98.50%,其断裂韧性和硬度分别为8.13 MPa·m~(1/2)和21.81 GPa。随着烧结温度的升高,致密度增大,硬度也随之升高。温度达到1320°C时,硬度达到最高值22.58 GPa。继续升高温度,晶粒粗化导致硬度降低,但断裂韧性随温度升高不断增大。烧结温度为1360°C时,纯WC试样的硬度为23.92 GPa,当ZrO_2含量增加至14 wt%时,材料的硬度降低至21.3 GPa,但韧性却由4.04 MPa·m~(1/2)大幅度提高至9.60 MPa·m~(1/2)。WC-ZrO_2复合材料断裂主要表现为穿晶断裂,ZrO_2颗粒阻碍了裂纹的扩展,使裂纹发生偏转、绕行和桥接,增加裂纹扩展路径,从而达到增韧的效果。     

烧结温度对原位反应TiB2/B4C复合材料的组织与力学性能的影响

为了降低B_4C的烧结温度,提高B_4C断裂韧性,本文以B_4C、TiO_2、活性炭为原料,采用原位反应法热压烧结制备了TiB_2体积分数为10％的TiB_2/B_4C复合材料。探索了烧结温度对复合材料组织和力学性能的影响规律。结果表明,随烧结温度的提高,复合材料的抗弯强度和断裂韧性先增大后减小,在2050℃时有最大值,分别为544MPa和6.3MPa·m~(1/2),弹性模量和断裂韧性变化不大。随烧结温度的升高,基体和第二相晶粒逐渐长大。采用2050℃/1h/35MPa为最佳烧结工艺。     

凝胶注模制备碳化硼多孔陶瓷EI北大核心CSCD

以琼脂糖大分子为凝胶体系、聚丙烯酸为分散剂,采用凝胶注模工艺制备B4C坯体,经过1 800~2 000℃烧结,制备得到B4C多孔陶瓷。结果表明:pH值为7.5、分散剂含量为0.15%(体积分数)时,陶瓷浆料的稳定性和流动性最佳,制备得到固相含量为45%(体积分数)的低黏度陶瓷浆料。随着烧结温度升高,多孔陶瓷的通孔率下降,1 800℃烧结得到的块体通孔率为100%,气孔呈明显的单峰分布,孔径大小为1μm。多孔陶瓷的抗弯强度在60 MPa左右。Zr金属浸渗B4C多孔陶瓷后得到Zr C/Zr B2复合材料,其微观组织随渗层深度变化出现分层现象。     

凝胶-注模成型技术制备碳纤维/HA复合材料的研究

本文研究了pH值、分散剂、有机单体和碳纤维含量对碳纤维/HA陶瓷浆料粘度的影响,观察了复相陶瓷浆料的凝胶固化过程,研究了烧结温度和碳纤维含量对复合材料烧结密度、抗弯强度和断裂韧性的影响.研究结果表明:当pH =9、有机单体含量为10wt％、分散剂含量为5wt％、固相含量为50wt％的碳纤维/HA陶瓷浆料具有良好的分散性.随引发剂、催化剂含量的增加,复相陶瓷浆料的凝胶固化时间缩短.复合材料的烧结密度、抗弯强度和断裂韧性均随烧结温度的升高而升高.复合材料的抗弯强度和断裂韧性均随着碳纤维含量的增加呈现先增加而后降低趋势.当碳纤维含量为2wt％和2.5wt％时,凝胶注模成型所制备的复合材料的抗弯强度和断裂韧性分别为80.6 MPa和1.87 MPa·m1/2,较干压成型样品提高了24.9％和19.8％.     

凝胶注模制备碳化硼多孔陶瓷

以琼脂糖大分子为凝胶体系、聚丙烯酸为分散剂,采用凝胶注模工艺制备B4C坯体,经过1 800~2 000℃烧结,制备得到B4C多孔陶瓷。结果表明:pH值为7.5、分散剂含量为0.15%(体积分数)时,陶瓷浆料的稳定性和流动性最佳,制备得到固相含量为45%(体积分数)的低黏度陶瓷浆料。随着烧结温度升高,多孔陶瓷的通孔率下降,1 800℃烧结得到的块体通孔率为100%,气孔呈明显的单峰分布,孔径大小为1μm。多孔陶瓷的抗弯强度在60 MPa左右。Zr金属浸渗B4C多孔陶瓷后得到Zr C/Zr B2复合材料,其微观组织随渗层深度变化出现分层现象。     

针刺石英纤维预制体增强石英陶瓷复合材料的制备研究

以针刺石英纤维预制体、硅溶胶等为原料,采用溶胶-凝胶的方法制备了石英纤维增强石英陶瓷复合材料。研究了热处理温度对纤维形貌和纤维布拉伸性能的影响以及烧结温度对复合材料弯曲强度的影响。结果表明:石英纤维预制体经丙酮浸泡烘干后,经450℃热处理2h,可以完全去除纤维表面的浸润剂;复合材料经450℃烧结2h,材料弯曲强度为78.5MPa,拉伸强度为31.8MPa,抗压强度为88.8MPa,可以达到天线罩材料力学性能的要求。     

层厚比和硬夹层组成对B_4C-BNNTs/TiB_2-B_4C层状陶瓷复合材料性能的影响

以B_4C为基体层材料,BNNTs为基体层补强增韧剂,TiB_2为硬夹层,采用水基流延成型和热压烧结工艺制备了B_4C-BNNTs/TiB_2-B_4C层状陶瓷复合材料。研究了基体层与硬夹层的层厚比、硬夹层组成和烧结温度对层状陶瓷复合材料的显微结构和力学性能的影响。实验结果表明:当层厚比为1,硬夹层组份为80 wt%TiB_2+20 wt%B_4C,烧结温度为2050℃时,可以制备出力学性能良好的B_4C-BNNTs/TiB_2-B_4C层状陶瓷复合材料,其抗弯强度和断裂韧性分别达到570.54 MPa和7.74 MPa·m~(1/2)。     

Al-MoSi2-TiC陶瓷基复合材料的研究

研究了Al-MoSi2-TiC陶瓷基复合材料的烧结工艺;利用MoSi2高温蠕变的特性促进TiC粉料的高温烧结：探讨了添加少量的金属铝粉对复合材料力学性能的影响;用SEM扫描电镜和x一射线衍射对复合材料显微形貌和晶体结构进行了表征。结果表明,MoSi2降低了TiC的烧结温度;制备的复合材料中除了TiC之外,还生成了新物相Mo,C,TiSi2和C：金属铝均匀分布在复合材料基体中,明显提高了材料的力学性能,抗折强度由50MPa提高到90MPa,抗压强度由55MPa提高到180MPa,同时其热膨胀系数随Al增加逐渐增大;讨论了Al-MoSi2-TiC陶瓷基复合材料的断裂机理。     

(SiC,TiB2)/B4C复合材料的微观结构及性能

以B4C与Si3N4和少量SiC,TiC为原料,Al2O3和Y2O3为烧结助剂,烧结温度为1 800～1 880℃,压力为30 MPa的热压条件下制备(SiC,TiB2)/B4C复合材料.用透射电子显微镜、扫描电子显微镜和能谱分析进行显微结构分析.结果表明:在烧结过程中反应生成了SiC,TiB2和少量的BN.复合材料的主晶相之间有长棒状架构弥散相和束状弥散相,在部分B4C晶粒内部出现了内晶结构.结合对复合材料性能的分析表明:新形成相、均匀细晶和棒状结构对提高材料的性能具有重要作用.通过对材料断口形貌和裂纹扩展模式分析认为,复合材料的断裂机制主要为裂纹偏转.     

High temperature bending properties and failure mechanism of 3D needled C/SiC composites up to 2000 ℃

Three-dimensional (3D) needled C/SiC composites were prepared and subjected to three-point bending tests from room temperature (RT) to 2000 ℃ under vacuum. The results show that the flexural strength and modulus increase in the range of RT to 800 °C due to the release of thermal residual stress (TRS). At 800–1700 °C, the modulus further increases for the further release of TRS, while the destruction of the pyrolytic carbon (PyC) coating reduces the flexural strength. Up to 2000 ℃, the thermal mismatch stress in the composites cause fiber slippage and matrix crack deflection to be zigzag, which increase the fracture strength. The change of components properties mediated by high temperature and the release of TRS play a leading role in the flexural strength and fracture mode. The results provide important support for the mechanical behavior of 3D needled C/SiC composites at ultra-high temperature.     

Effect of carbon fabric type on the mechanical performance of 2D carbon/carbon composites

A stabilized PAN fabric was carbonized and graphitized from 800°C to 2500°C. Two-dimensional (2D) carbon/carbon composites were made using the stabilized PAN fabric, carbonized fabrics, and a resol-type phenol-formaldehyde resin. These composites were heat-treated from 600°C to 2500°C. The influence of different heat-treated fabrics and heat treatment on the fracture and flexural strength of these composites was also studied. The composite reinforced with higher heat-treated fabrics showed a lower weight loss than that with lower heat-treated fabrics. When the composites were graphitized at 2500°C, the loss was 49.7 wt% for the composite made with stabilized PAN fabric and 26 wt% for that with carbonized fabric at 2500°C. Those composites also have a higher density than composites produced by other methods. Composites made with stabilized PAN fabric exhibited a strong bonding in the fiber/matrix during pyrolysis. This composite showed catastrophic fracture and a smooth fracture surface with no fiber pullout. Composites made with higher carbonized fabrics exhibited a weak interface bonding. These composites showed a pseudo-plastic fracture pattern with fiber pullout during pyrolysis. Composites made with carbonized fabrics at 2000°C and 2500°C showed the highest flexural strength at the prolysis temperature of 1000°C. Composites made with carbonized fabric at 1300°C showed the highest flexural strength above 1500°C to 2500°C. The composite made with stabilized PAN fabric exhibited the lowest flexural strength during pyrolysis.     

Effects of sintering temperature on mechanical properties of 3D mullite fiber (ALF FB3) reinforced mullite composites

A new method to weaken the interfacial bonding and increase the strength of 3D mullite fiber reinforced mullite matrix (Mu_f/Mu) composites is proposed and tested in this paper. Firstly, Mu_f/Mu composites were fabricated through sol–gel process with varied sintering temperature. Then, the effects of sintering temperature on mechanical properties of the composites were tested. As sintering temperature was raised from 1000 °C to 1300 °C, the three-point flexural strength of the composites firstly decreased from 66.17 MPa to 41.83 MPa, and then increased to 63.17 MPa. In order to explain the relationship between composite strength and sintering temperature, morphology and structure of the mullite fibers and mullite matrix after the same heat-treatment as in the fabrication conditions of the composites were also investigated. Finally, it is concluded that this strength variation results from the combined effects of matrix densification, interfacial bonding and fiber degradation under different sintering temperatures.     

Weak interface dominated high temperature fracture strength of carbon fiber reinforced mullite matrix composites

Weak fiber/matrix interface dominates the toughening properties of ceramic matrix composites. This paper reports a novel sol-gel fabricated carbon fiber reinforced mullite matrix composite, in which the fiber/matrix interface was inherently weak in shear properties (∼25 MPa), measured in-situ by fiber push-in tests. The interface microstructure was chemically sharp, characterized by transmission electron microscopy. The outcome of the weak interface was the full trigger of the toughening mechanisms like crack deflection, etc., leading to significant enhancement of the fracture toughness of the composite (∼12 MPa√m), measured by single edged notch beam method. Finally, due to the weak fiber/matrix interface and large thermal expansion mismatch of the fiber and matrix, the high temperature fracture strength was enhanced in the temperature range from 25 to 1200 °C, which is attributed to the enhancement of the interfacial property at elevated temperatures that favors better load transfers between composite constituents.     

Processing and mechanical performance of 3D Cf/SiCN composites prepared by polymer impregnation and pyrolysis

The processing of 3D carbon fiber reinforced SiCN ceramic matrix composites prepared by polymer impregnation and pyrolysis (PIP) route was improved, and factors that determined the mechanical performance of the resulting composites were discussed. 3D C_f/SiCN composites with a relative density of ∼81% and uniform microstructure were obtained after 6 PIP cycles. The optimum bending strength, Young's modulus and fracture toughness of the composites were 75.2 MPa, 66.3 GPa and 1.65 MPa m^1/2, respectively. The residual strength retention rate of the as-pyrolyzed composites was 93.3% after thermal shock test at ΔT = 780 °C. It further degraded to 14.6% when the thermal shock temperature difference reached to 1180 °C. The bending strength of the composites was 35.6 MPa after annealing at 1000 °C in static air. The deterioration of the bending strength should be attributed to the strength degradation of carbon fibers and decomposition of interfacial structure.     

The effect of pyrolysis on the mechanical properties and microstructure of carbon fiber-reinforced and stabilized fiber-reinforced phenolic resins for carbon/carbon composites

Carbon/carbon composites were prepared with phenol-formaldehyde resin, one kind of commercial carbon fiber, and a stabilized fiber that was developed in our laboratory. The effect of pyrolysis on the microstructure, fracture behavior, and flexural strength of the composites during the carbonization process was studied. During the pyrolysis of the composites a chemical reaction at the fiber/resin interface apparently took place. A thermogravimetry (TG) study indicated that the use of stabilized fiber reinforced composites inhibited decomposition reactions and thermal fragmentation in the matrix resin, and reduced the weight loss of the final composites. The X-ray reflection of the resin and the two composites showed a reflection appearing at 2θ ≈ 12° when the samples were carbonized above 600°C. The intensity of this reflection in the composites made with stabilized fiber was higher than that of the composite made with carbon fiber. Because of the formation of strong bonding in the fiber-matrix interface, the composites made with stabilized fiber showed catastrophic failure and low flexural strength below carbonization temperatures of 600°C. Above 600°C, the flexural strength of the composites increased with an increase in the carbonization temperatures, even if the fracture behaviors showed catastrophic failure. The flexural strength of the composites made with carbon fiber showed pseudo-plastic patterns and debonding with very little fiber pullout. Above 800°C, these composites showed a catastrophic failure and smooth failure surfaces. During pyrolysis the flexural strength decreased with an increase in the carbonization temperature.     

Improving delamination resistance of carbon fiber reinforced polymeric composite by interface engineering using carbonaceous nanofillers through electrophoretic deposition: An assessment at different in-service temperatures

In this article, modification of carbon fiber surface by carbon based nanofillers (multi-walled carbon nanotubes [CNT], carbon nanofibers, and multi-layered graphene) has been achieved by electrophoretic deposition technique to improve its interfacial bonding with epoxy matrix, with a target to improve the mechanical performance of carbon fiber reinforced polymer composites. Flexural and short beam shear properties of the composites were studied at extreme temperature conditions; in-situ cryo, room and elevated temperature (−196, 30, and 120°C respectively). Laminate reinforced with CNT grafted carbon fibers exhibited highest delamination resistance with maximum improvement in flexural strength as well as in inter-laminar shear strength (ILSS) among all the carbon fiber reinforced epoxy (CE) composites at all in-situ temperatures. CNT modified CE composite showed increment of 9% in flexural strength and 17.43% in ILSS when compared to that of unmodified CE composite at room temperature (30°C). Thermomechanical properties were investigated using dynamic mechanical analysis. Fractography was also carried out to study different modes of failure of the composites.     

Fabrication of C/C-SiC composites using high-char-yield resin

Carbon fiber reinforced ceramic matrix composites (C/C-SiC composites) were fabricated using a type of high-char-yield phenolic resin with the char yield of 81.17 wt.%. Firstly, the fabric prepreg was prepared by spreading the phenolic resin solution onto the two dimensional carbon fiber plain weave fabric and dried consequently. Afterward, the resin was cured and then the carbon fiber reinforced polymer (CFRP) was pyrolyzed to get amorphous carbon. Finally, C/C-SiC composites were obtained through liquid silicon infiltration (LSI) process. SEM micrographs showed that the Si/SiC area was homogeneously dispersed in the matrix, and during the siliconization process, a layer of SiC was formed along the surface of carbon fibers or carbon matrix. The fiber volume of CFRP was about 40 vol.%, which was much lower than other studies. XRD result indicated that only β-SiC type was formed. The result of X-ray computed tomography clearly showed the structure changes before and after the melt infiltration process. Mechanical property test showed that the composites had fracture strength of 186 ± 23 MPa, and a flexural modulus of 106 ± 8 GPa.     

Oxidation and recession of plain weave carbon fiber reinforced ZrB2-SiC-ZrC in oxygen–hydrogen torch environment

The oxidation and recession of four plain weave carbon fiber reinforced ZrB₂-SiC-ZrC composites with different matrix compositions were compared with those of a plain weave carbon fiber reinforced ZrB₂-SiC matrix composite. These composites were fabricated using a silicon melt infiltration method. The composite with the higher ZrC content also formed ZrSi₂ in the matrix instead of residual silicon. The composites were oxidized at 1700 and 1800 °C in an oxygen–hydrogen torch environment. The oxides consisted of ZrO₂ and SiO₂, which formed on the surface of all samples. Carbon fiber at the surface was lost due to oxidation. The recession resistance of ZrB₂-SiC-ZrC matrix composites remained constant at 1700 °C, even if the matrix composition varied, while the resistance at 1800 °C increased with the matrix of ZrC and ZrSi₂. The ZrB₂-SiC-ZrC matrix composite with the higher ZrC and ZrSi₂ compositions formed a sintered ZrO₂-rich layer, which was denser than the ZrO₂-SiO₂ and improved the recession resistance.     

Enhanced mechanical properties of lightweight Al2O3-C refractories reinforced by combined one-dimensional ceramic phases

We prepared a new lightweight Al₂O₃-C refractory material with a higher strength by using microporous corundum aggregates instead of dense tabular corundum aggregates, which was reinforced by in situ formed SiC whiskers, multi-walled carbon nanotubes (MWCNTs), and mullite rods. A comparative study of the microstructure, mechanical properties, and fracture behavior was carried out for dense and lightweight Al₂O₃-C refractories coked at 1200°C and 1400°C, respectively. By using the microporous corundum aggregates, a better aggregate/matrix interface bonding and an optimized distribution of SiC whiskers were obtained. The SiC whiskers formed inside the microporous corundum aggregates and simultaneously in the matrix by a vapor-solid reaction mechanism, resulting in an enhancement at the microporous aggregate/matrix interface. Furthermore, the in situ formed MWCNTs and well-developed mullite rods at 1200°C in the matrix also contributed to the better interface structure. Thus, due to the improved microporous aggregate/matrix interface, the crack propagation along the aggregate/matrix interface was suppressed, resulting in an increased crack propagation within the aggregates. Consequently, the synergy between microporous corundum aggregates and combined one-dimensional ceramic phases caused a lower bulk density but a markedly higher strength, a higher fracture energy, and a higher toughness of lightweight Al₂O₃-C refractories compared to the dense ones. Overall, our study allows to overcome the traditional concept that a higher strength of refractories is reached by a higher density.