三维织物碳／碳复合材料中层间剪切强度的改进

碳纤维增强碳(C/C)复合材料是由沥青基碳纤维粗纱纺织的多层织物和煤沥青基体构成的,本次实验研究了两种C/C多层织物复合材料和一种平纹编织C/C布复合材料,测试了弯曲、剪切和压缩强度。根据不同跨距--高度比下的三点弯曲试验结果,表明C/C1多层织物复合材料具有高的剪切性能,多层织物复合材料的分层断裂比平纹编织C/C布复合材料具有更高的层间断裂韧性。     

复合材料带缠绕张力参数对碳/酚醛材料层间剪切强度影响研究

目前缠绕工艺参数对制品层间剪切强度的影响研究多集中于3k碳布或高硅氧布为增强体的复合材料,而一体化复合材料喷管制品烧蚀层常采用1k碳布/酚醛材料进行制备。因3k碳布和1k碳布稀疏特性存在本质区别,将影响酚醛树脂固化过程中产生小分子挥发物的排出效率,从而导致制品性能存在差异。为揭示带缠绕张力对1k碳布/酚醛制品层间性能的影响,采用湿法预浸工艺制备1k碳布/酚醛预浸带,基于控制变量法设计缠绕参数,通过数控布带缠绕机缠绕试样环,设计层间剪切测试工装,实现对试样整环的层间剪切强度测试。结果表明,选用张力系数为20N/cm制备的试样环性能最低,平均值为16.996Mpa;张力系数在30N/cm至70N/cm范围内,制品层间剪切强度波动较为平缓,无明显变化趋势。     

二维C/(BCχ-SiC)n复合材料的高温层间剪切性能

采用双槽口剪切法(double-notchcd shear,DNS)研究了二维(twodimensional,2D)碳乡纤维增强碳化硼-碳化硅[2DC/(BCx-SiC)]复合材料的高温层间剪切性能,用扫描电子显微镜观察断口彤貌.结果表明:在25～1200℃范围内.温度对2DC/(BCx-SiC)n复合材料的层间剪切强度有明显影响,在900℃时材料的层间剪切强度最高可达40.0MPa,分别比25℃和1200℃的商约13%和8%,略高于700℃的.此外,C/(BCx-SiC)n的层间剪切强度始终高于C/SiC的强度,且2种材料的层间剪切强度随温度变化规律相似.断口分析表明:层间剪切失效发生在基体内部或基体/纤维界面上,而纤维并没有受到损伤.     

纤维热处理对C/C-SiC复合材料剪切强度的影响

对T300碳纤维在真空环境下,在600、900、1200、1500℃进行热处理,用液硅熔渗反应法(liquid silicon infiltration,LSI)制备了不同微观组织结构的C/C-SiC复合材料。采用光电子能谱分析了热处理对纤维表面结构的影响,用光学显微镜和扫描电子显微镜对材料微观形貌进行了观察分析。采用双槽口剪切法(DNS)测试了C/C-SiC复合材料层间剪切强度(interlaminar shear strengh,ILSS),并分析了纤维热处理对材料剪切性能影响的微观机理。结果表明：碳纤维经热处理后,表面化学成分发生变化,氧含量显著降低,改变了碳纤维增强树脂基复合材料(carbon fiber reinforced resin matrix composite,CFRP)先驱体中纤维/树脂界面结合强度,从而在CFRP裂解后形成了具有不同微观结构的C/C预制体,通过液Si对不同微结构的C/C预制体进行熔渗,获得具有不同微观结构的 C/C-SiC复合材料;DNS 测试发现碳纤维热处理能够有效改善 C/C-SiC复合材料的层间剪切强度,主要是由于纤维经热处理后制备的C/C-SiC复合材料中,SiC基体相分布较均匀并包裹在碳纤维周围,导致纤维/基体界面结合强度高。经1500℃热处理纤维增强的C/C-SiC复合材料,其剪切强度为34 MPa,与未处理的相比,ILSS提高了33%。     

芳纶纤维/AFR树脂复合材料界面粘结性能的研究

为了改善芳纶纤维复合材料的界面粘结性能,合成了一种新型树脂(AFR)作为基体,以未经任何表面处理的芳纶纤维作增强材料,制备了芳纶纤维/AFR复合材料。采用测定表面能、接触角、层间剪切强度、横向拉伸性能和扫描电镜观察形貌等方法,从宏观和微观等方面研究了芳纶纤维/AFR复合材料的界面粘结性能。结果表明,AFR树脂与芳纶纤维有相近的表面能,AFR树脂溶液与芳纶纤维的接触角为42.8°,而环氧树脂(EP)与芳纶纤维的接触角为68°,说明AFR树脂对芳纶纤维的润湿性优于EP树脂;芳纶/AFR复合材料的层间剪切强度、横向拉伸强度和纵向拉伸强度分别为74.64MPa、25.34MPa和2256MPa,比芳纶/EP复合材料的相应强度分别提高了28.7%、32.5%和13.4%,其复合材料破坏面的形貌也说明芳纶纤维与AFR树脂之间的界面粘结性能较好。     

酚醛改性聚芳基乙炔基复合材料探索

聚芳基乙炔（PAA）树脂具有残碳率高、吸水率低、固化反应为加聚反应、无低分子物副产物逸出等特点,是专为新一代树脂基热防护复合材料而研制的。但其与碳布的浸润性及粘接性能差,碳布增强复合材料的剪切强度较低。本文采用酚醛树脂对PAA树脂进行改性处理,在不降低残碳率的情况下,明显改善了PAA树脂与碳布的粘接性能。改性后碳／聚芳基乙炔复合材料的剪切强度由5．5MPa提高到11MPa以上。     

三维针刺C/SiC复合材料的结构特征和力学性能

采用化学气相渗透法制备了在厚度方向上具有纤维增强的三维针刺碳纤维增强碳化硅(C/SiC)陶瓷基复合材料,复合材料的密度和气孔率分别为2.15 h/cm3和16%.三维针刺C/SiC复合材料中的针刺纤维将各层紧密结合在一起,其层间抗剪切强度显著提高,为95MPa,比二维碳布叠层C/SiC复合材料的剪切强度(35MPa)高171.4%.三维针刺C/SiC复合材料的拉伸强度和弯曲强度分别为159MPa和350MPa,断裂模式为非脆性断裂,包括:裂纹扩展、偏转,碳纤维的拉伸断裂和逐步拔出.     

RTM成型针刺预制体增强糠酮树脂烧蚀复合材料性能研究

以炭布/炭网胎叠层针刺预制体为增强体,糠酮树脂为基体,采用RTM工艺制备出表面质量良好的复合材料,对复合材料的力学及烧蚀性能进行测试分析.结果表明,制备的复合材料具有良好的力学性能特别是层间剪切强度,高达66.3MPa;氧-乙炔线烧蚀率为0.0368mm/s,质量烧蚀率为0.0865g/s,烧蚀性能较好.     

不同温度下T700/环氧复合材料层间剪切强度（ILSS）统计分析

本文根据25℃-125℃不同温度条件下的碳纤维/环氧复合材料层间剪切强度实验数据,利用统计学中的线性回归分析法,对不同温度下T700/环氧复合材料的层间剪切强度进行拟合,得到了回归方程,为预判、检验碳/环氧复合材料性能提供参考依据。并预测了125℃下层间剪切强度最小值为31.23MPa,通过与实测数据比较,吻合较好。     

二维C/(BC_x–SiC)_n复合材料的高温层间剪切性能(英文)

采用双槽口剪切法(double-notched shear,DNS)研究了二维(two dimensional,2D)碳纤维增强碳化硼-碳化硅[2DC/(BCx-SiC)n]复合材料的高温层间剪切性能,用扫描电子显微镜观察断口形貌。结果表明:在25～1200℃范围内,温度对2DC/(BCx-SiC)n复合材料的层间剪切强度有明显影响,在900℃时材料的层间剪切强度最高可达40.0MPa,分别比25℃和1200℃的高约13%和8%,略高于700℃的。此外,C/(BCx-SiC)n的层间剪切强度始终高于C/SiC的强度,且2种材料的层间剪切强度随温度变化规律相似。断口分析表明:层间剪切失效发生在基体内部或基体/纤维界面上,而纤维并没有受到损伤。     

Influence of graphitization treatment on microstructure and flexural strength of C/C-ZrC-SiC composites fabricated via reactive melt infiltration

C/C-ZrC-SiC composites were prepared by chemical vapor infiltration (CVI) and molten salt assisted reactive melt infiltration (RMI). The microstructure of low density and high density C/C composites without graphitization (LC/HC) and graphitization at 2000 °C (LCG/HCG) were compared. Moreover, the effects of graphitization of LC and HC on the microstructure and flexural strength of C/C-ZrC-SiC composites were investigated in detail. The composites prepared by infiltration of LC and LCG had lower flexural strength, 220.01 ± 21.18 MPa and 197.94 ± 19.05 MPa, respectively. However, the composites prepared by HC and HCG presented higher flexural strength, 308.76 ± 12.35 MPa and 289.62 ± 8.70 MPa, respectively. This was due to the phenomenon of fiber erosion in both LC and LCG during the RMI process. After graphitization, the flexural strength of C/C-ZrC-SiC composites prepared by RMI decreased, but the fracture behavior of the composites tends to be more mild. The decreased strength of the composites were caused by the increased matrix cracks, fiber damage in high temperature and the weak interfacial bonding. The improve of failure behavior of the composites was due to interface debonding between the fiber and matrix, and composites can consume the fracture energy through fiber pull-out.     

Fabrication and optimization of 3D-Cf/HfC-SiC-based composites via sol-gel processing and reactive melt infiltration

In this work, 3D-C_f/HfC-SiC-based composites were fabricated and optimized via reactive melt infiltration (RMI) of Si into porous C_f/HfC-C preforms prepared by a sol-gel processing. The physical and chemical processes involved during the fabrication were identified and analyzed in details. It is revealed that fibers and interphase of the composites can be eroded during carbothermal reduction process, which can be further aggravated during RMI, with the formation of Hf-containing substance on the fibers surface. The fibers and interphase degradation is mainly induced by the reactions between HfO₂ and C/SiC interphase layers at elevated temperatures. Accordingly, a two-step carbothermal reduction treatment was proposed for the optimization of the fabrication procedure. As a result, less fiber/interphase erosion and improved mechanical properties are achieved in the composites, with the bending strength increased by ～49 % (from 214.1 ± 15.7 MPa to 319.0 ± 26.0 MPa).     

三维打印制备MAX基复相陶瓷研究进展

本文综述了三维打印(Three-Dimensional Printing,3DP)结合反应熔体渗透(Reactive Melt Infiltration,RMI)技术制备MAX基复相陶瓷的研究进展。在致密MAX基复相陶瓷的制备过程中,3DP技术的作用主要体现在两方面:一方面是实现预制体的成型,另一方面是通过孔隙结构和成分的设计控制所制备材料的微结构。3DP所制备的预制体呈现为典型的双孔径分布模式,有利于RMI的进行。通过3DP同RMI结合能够实现致密MAX基复相陶瓷的近尺寸成型,同时通过对初始原料、渗透熔体以及渗透温度等参数的优化能够实现微结构、力学性能以及电磁屏蔽性能的调控。     

碳纤维增强超高温陶瓷基复合材料的多相反应制备与抗烧蚀性能

为提高C/C复合材料在2000℃以上有氧环境中的抗氧化烧蚀性能,本研究采用ZrB₂浆料浸渍、ZrC-SiC前驱体浸渍裂解与Si-Zr10共晶合金反应熔渗复合工艺制备了C/C-SiC-ZrB₂-ZrC复合材料,细致研究了复合材料在熔渗过程中的基体微观结构演变机理及其力学性能和抗烧蚀性能。结果表明,在反应熔渗结束后的降温阶段,部分ZrC陶瓷与残余Si熔体通过原位固-液反应转化为ZrSi₂和SiC,生成的亚微米级SiC颗粒均匀镶嵌于ZrC-ZrSi₂二元混合物中,最终形成ZrC-ZrSi₂-SiC三相混合微区。制备的C/C-SiC-ZrB₂-ZrC复合材料密度为3.18 g/cm³,开孔率为2.77%,其弯曲强度和弯曲模量分别为121.46±13.77 MPa和21.78±5.56 GPa。在其断口处能观察到较长且较多的单丝纤维拔出以及明显的界面脱黏,这表明复合材料的失效方式为韧性断裂。经2000℃,300 s的大气等离子体烧蚀,复合材料表...     

Microstructures and properties of Si-Zr alloy based CMCs reinforced by various porous C/C performs

C/C-SiC composites were fabricated via Si-Zr reactive alloyed melt infiltration using various C/C preforms with different porosities as reinforcements. The influence of preform porosities on the microstructure, mechanical strength and ablation resistance of the as-prepared composites were investigated. The results indicated that microstructure and properties of the C/C-SiC composites seriously depended on C/C preform porosities. The composites were mainly composed of carbon, SiC and ZrSi₂ phases, while some residual silicon still existed in the composites prepared with very large porosity preforms. Flexural strength of the composites firstly increased with increasing C/C preform porosities, then reached the highest value, 307?MPa, and finally turned to decrease with the further increasing of preform porosities. Densities of the composites increased with increasing preform porosities, while open porosities were generally small below 7%. Linear ablation rates of the composites firstly sharply decreased with increasing preform porosities and then slightly decreased to reach a balance value. In a word, C/C preform porosity was of great significance for reactive melt infiltration of C/C-SiC composites. Densities, microstructure, mechanical strength and ablation resistance of the resulting composites should be comprehensively taken into consideration to choose an optimal preform porosity for fabrication of C/C-SiC composites.     

Carbon fiber/reaction-bonded carbide matrix for composite materials – Manufacture and characterization

The processing of self-healing ceramic matrix composites by a short time and low cost process was studied. This process is based on the deposition of fiber dual interphases by chemical vapor infiltration and on the densification of the matrix by reactive melt infiltration of silicon. To prevent fibers (ex-PAN carbon fibers) from oxidation in service, a self-healing matrix made of reaction bonded silicon carbide and reaction bonded boron carbide was used. Boron carbide is introduced inside the fiber preform from ceramic suspension whereas silicon carbide is formed by the reaction of liquid silicon with a porous carbon xerogel in the preform. The ceramic matrix composites obtained are near net shape, have a bending stress at failure at room temperature around 300 MPa and have shown their ability to self-healing in oxidizing conditions.     

低压化学气相渗透法制备2.5维SiCf/SiC复合材料

采用低压化学气相渗透法制备了具有和不具有热解炭界面层的2.5维连续SiC纤维增强的SiC复合材料(SiCf/SiC).SiC纤维的体积分数为30%和41%.所制备复合材料的气孔率为20%左右.当纤维为30%时,沉积有0.1 μm热解炭界面层的复合材料的弯曲强度由未加热解炭界面层的232MPa增加到328MPa,而且材料由灾难性断裂转变为非灾难性断裂.在同一制备条件下,纤维体积分数为41%的SiCf/SiC比30%的SiCf/SiC具有更高的气孔率.纤维为41%时,热解炭界面层厚度为0.1 μm的SiCf/SiC的弯曲强度只有244MPa,但是它具有更高的韧性和更长的纤维拔出长度.     

Microstructure and flexural strength of C/HfC-ZrC-SiC composites prepared by reactive melt infiltration method

C/HfC-ZrC-SiC composites were fabricated via reactive melt infiltration (RMI) of the mixed HfSi₂ and ZrSi₂ alloys. The microstructure, infiltration behavior of the hybrid silicide alloys infiltrating C/C composites, and flexural strength of C/HfC-ZrC-SiC composites was studied. Inside composites, there were more Hf-rich (Hf, Zr)C phases distributed in the exterior region, while more SiC and Zr-rich (Zr, Hf)Si₂ in the interior region. There was compositional segregation in (Hf, Zr)C, with the HfC content decreasing from the exterior region to interior region. The RMI process was performed at different temperatures to investigate the structural evolution, and a model for the reactive melt infiltration of the mixed HfSi₂ and ZrSi₂ alloys into C/C composites was established. Compared with C/HfC-SiC and C/ZrC-SiC prepared by same process, C/HfC-ZrC-SiC had the highest flexural strength of 247Mpa and 213Mpa after oxidation at 1200 ℃ for 15 min. Both the unoxidized and oxidized samples presented a pseudo-plastic fracture behavior.     

Reactive melt infiltrated Cf/SiC composites with robust matrix derived from novel engineered pyrolytic carbon structure

Needle-punched C_f/SiC composites were fabricated by a novel pore tuned reactive melt infiltration (RMI) process. The novel hierarchically porous carbon structure in the fiber preform with the porosity well open to liquid silicon was engineered by impregnation of phenolic resin with addition of a pore former. Neither residual bulk carbon nor residual bulk silicon is detected in the matrix of the C_f/SiC composites prepared by the pore tuned RMI, indicating that a robust matrix with homogenous SiC can be formed. The composite prepared by the pore tuned RMI exhibits a tensile strength of 159±5 MPa, which is 46% higher than that without addition of pore former.