针刺炭纤维预制体的发展与应用

对比了国内外针刺炭纤维预制体的发展与应用.法国Sneema公司采用针刺技术成型的预制体有Novoltex和Naxeco两种,应用于火箭发动机延伸锥、喉衬等.国产薄壁针刺C/C复合材料性能与法国针刺扩张段材料性能相当.国产针刺预制体有整体毡和炭布/网胎针刺预制体,炭布/网胎叠层针刺预制体由于x-y向引入了连续纤维,制品整体性能较好.针刺技术是炭纤维预制体的自动化成型技术,拓宽了C/C复合材料应用领域.     

化学气相沉积致密针刺C/C复合材料的结构及力学性能研究

以T300炭纤维无纬布、网胎为原材料,层叠针刺成型炭纤维预制体,并采用化学气相沉积工艺对预制体进行致密,制成密度为1.55 g/cm3的针刺C/C复合材料。对针刺C/C复合材料的微观结构进行了观察分析,并对材料力学性能进行了测试。结果表明:化学气相沉积致密的针刺C/C复合材料呈现出以层间大量垂直纤维束为节点的类钉板状网状结构,这种特殊结构使材料层间结合更好,材料整个结构更加紧密;针刺C/C复合材料内部纤维被沉积形成的热解炭所包裹,热解炭的织构类型为光滑层(SL)和粗糙层(RL)并存;针刺C/C复合材料的各项力学性能均达到了较高水平,并且高温力学性能比常温力学性能有了很大幅度的提高。     

致密工艺对C/C复合材料摩擦性能的影响

采用针刺全炭纤维网胎无纬布整体结构预制体为骨架，经化学气相沉积（CVD）、树脂浸溃（RD固化致密及炭化、石墨化制得C／C复合材料。研究了粗糙层（RL）和树脂炭（RC）对摩擦性能的影响。结果表明，RL结构的C／C复合材料的摩擦性能较好，稳定性较高，是用作飞机刹车材料的前提；采用CVD＋RI制备且石墨化后的C／C复合材料具有优良的摩擦磨损特性；CVD试样的密度较低时，摩擦系数较高，但磨损较大，较难形成完整的摩擦膜。     

纤维编织结构对C/C复合材料摩擦磨损性能的影响

在MM-1000摩擦磨损试验机上对炭纤维无纬布层(简称炭布层)和炭纤维网胎层(简称网胎层)针刺结构的炭/炭(C/C)复合材料的摩擦磨损性能进行了研究,并采用光学显微镜和扫描电镜(SEM)对C/C复合材料的摩擦表面和磨屑进行了观察和分析。结果表明:与网胎层C/C复合材料相比,炭布层C/C复合材料的摩擦磨损性能更好;当制动压力为0.6 MPa、制动速度为26 m/s时,网胎层C/C复合材料的平均摩擦系数为0.36、质量磨损率为12.8 mg/次、制动时间为15.2 s;而炭布层的平均摩擦系数为0.38,质量磨损率为10.5 mg/次,制动时间为14.9 s。     

不同增强结构炭/炭复合材料力学及抗烧蚀性能

分别采用轴棒法编织、轴向穿刺以及无纬布/网胎针刺3种结构预制体,经致密化处理得到高密度C/C复合材料,研究了材料力学性能、抗烧蚀性能,并评价了3种增强结构材料的整体性能。结果表明,C/C材料轴向拉伸强度与预制体轴向纤维含量、纤维连续状态有关。轴向穿刺、轴棒法C/C材料轴向拉伸强度明显高于无纬布/网胎针刺C/C材料,但无纬布/网胎针刺C/C材料的径向压缩强度最高。经300 s氧-乙炔烧蚀后无纬布叠层针刺C/C材料的线烧蚀率和质量烧蚀率最低,抗烧蚀最好,烧蚀过程主要受热化学烧蚀和机械剥蚀共同作用。     

RMI法制备C/C-SiC炭陶复合材料的热学性能研究

以针刺网胎无纬布为预制体,采用压力浸渍树脂/炭化工艺结合反应熔体浸渗法(RMI)快速制备C/C-SiC炭陶复合材料。研究了炭陶复合材料在室温~800℃时的热扩散系数、比热容和导热系数等热学性能参数和在室温~1 000℃时的热膨胀系数。结果表明:x-y向(平面方向)和z向(厚度方向)的比热容和热膨胀系数呈非线性增大,而热扩散系数和导热系数则呈非线性降低;x-y向的热扩散系数及导热系数明显大于z向,表明炭陶材料呈各向异性;1 000℃时x-y向平均热膨胀系数为1.506×10~(-6)/℃,低于z向的平均热膨胀系数(3.666×10~(-6)/℃)。     

C/C复合材料预制体结构对摩擦性能的影响

采用整体毡预制体、针刺网胎/无纬布叠层预制体和穿刺预制体,通过化学气相沉积法(CVD)结合液相浸渍法(PIP)制备了C/C复合材料,利用MM1000-Ⅱ型摩擦磨损实验机测试了三种不同预制体C/C复合材料的摩擦性能,采用扫描电子显微镜分别观察了三种C/C复合材料的表面形貌,研究发现预制体结构中纤维排布方式及含量影响C/C复合材料的摩擦系数。相同转速下C/C复合材料的摩擦系数随压力的升高而增大;压力相同的条件下C/C复合材料的摩擦系数随着转速提高而增大;高压高转速下针刺网胎/无纬布制备的C/C复合材料摩擦系数较稳定,整体毡制备的摩擦系数虽小但随转速变化波动较大,穿刺预制体制备的摩擦系数大且波动大,说明穿刺这种增强单元相对较粗大的预制体不适合制备摩擦密封领域的精细结构复合材料。     

针刺成型C／C预制体的研究进展

预制体作为C／C复合材料的增强结构,它的发展必定会推动C／C复合材料应用于更广闾的领域。文章综述了针刺成型C／C预制体技术在国内外研究进展,并概述了影响针刺C／C预制体性能的主要因素,包括炭布、网胎以及针刺工艺参数等,并对我国针刺技术的发展提出了一些建议。     

炭／炭复合材料吊具制备及性能研究

针对高温处理炉使用环境气氛,采用针刺无纬布、网胎交替叠层的预制体,优化组合预制体中结构单元,经气相、液相相结合的致密方法增密后,经高于使用温度高温处理制得炭／炭复合材料吊具,并进行了力学、热学性能检测和微观形貌分析。经校核所研制炭／炭复合材料吊具达到负载2吨能力（安全系数2）,可与产品一起经历1400℃—2600℃高温处理过程,解决目前高温处理无随炉吊装工具的问题,实现在炉外装出产品整体吊装操作。     

针刺+缝合预制体C/C复合材料的制备及性能研究

以无纬布/碳纤维网胎为原料,采用针刺+接力缝合的工艺流程制备预制增强体,并经化学气相渗透(CVI)联合沥青浸渍/高压碳化(HPIC)方法得到新型厚壁C/C复合材料。对该材料进行了力学和热物理性能测试,并观测其微观断口形貌。结果表明:此预制体制备方法能够突破传统缝合材料在厚度方向上的尺寸限制,工艺过程简便,不易变形且利于致密。所得C/C材料厚度方向的纤维密度较高,具有优异的机械和良好的热物理性能,能够满足固体火箭发动机等极端环境下的应用需求。     

三维针刺C/SiC复合材料无纬布纤维方向对材料力学性能的影响

通过化学气相渗透法结合反应熔体浸渗法制备了三维针刺C/SiC复合材料,采用扫描电子显微镜观察材料的显微结构,并研究了无纬布纤维方向对材料力学性能的影响.结果表明,三维针刺C/SiC复合材料由O°无纬布层、短纤维胎网层、90°无纬布层以及针刺纤维束组成,无纬布层纤维方向对材料性能有显著影响.试样的拉伸强度和弯曲强度随着无纬布纤维方向与试样长度方向的夹角θ(0 ～45°)值的增大而减小,面内剪切强度和冲击韧性随θ角的增大而增大.     

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.     

Effects of fiber preform structures on the mechanical properties of C/SiC nuts and bolts

Carbon fiber-reinforced silicon carbide (C/SiC) nuts and bolts (M8) with different fiber preform structures were prepared by precursor infiltration and pyrolysis. The influences of fiber preform structures on the mechanical properties of C/SiC nuts and bolts, as well as the failure behaviors of threaded joints were studied. A C/SiC nut, which was fabricated by using the preform prepared by stacking 3K carbon fiber cloth followed by stitching, had the highest shearing strength (64.5 MPa). The bolt with the preform prepared by alternatively stacking 3 K carbon fiber cloth and unidirectional layer of carbon fiber tows followed by stitching had the highest extreme tensile strength (243.2 MPa) and shearing strength (106.3 MPa), but low thread tooth bearing ability (3.5 kN) and critical thread engagement length (9 mm). It is suitable for applications emphasizing the extreme tensile or shearing strengths of threaded joints or possessing enough thread engagement length to ensure bolt rupture as the failure mode. The bolt with the perform prepared by stacking 1K carbon fiber cloth followed by stitching had the highest thread tooth bearing ability (5.0 kN) and the lowest critical thread engagement length (6 mm), as well as moderate extreme tensile strength (163.0 MPa) and shearing strength (82.1 MPa). It works effectively for applications concerning thread tooth strength or possessing limited thread engagement length. Therefore, the preform for preparing a C/SiC bolt should be selected according to its application requirements.     

短纤维层间增强碳纤维复合材料层板的力学研究

以斜纹3k T300碳纤维布、环氧树脂和0.3~0.5 mm短切碳纤维为主要实验原料,使用短切纤维铺放装置将短切碳纤维定量铺放在碳纤维布表面,并铺层得到5块层间短切纤维增强的预制体,每块预制体含8层碳纤维布且每块预制体层间短切碳纤维铺放面密度分别为5,10,20,30,40 g/m2,并增设一块层数为8层、层间不含短切纤维增强的预制体作为对照组。采用真空辅助树脂灌注成型方式浸渍预制体后高温固化,得到层间含不同面密度短切纤维的碳纤维复合材料层合板,研究了不同面密度短切纤维含量对碳纤维复合材料层合板拉伸、弯曲以及层间剪切强度的影响。研究结果表明,当短切碳纤维铺放面密度为5 g/m2时,复合材料层板的拉伸、弯曲强度最好,在5~40 g/m2范围内,复合材料层板的层间剪切强度随短切碳纤维铺放面密度的增大而增大。     

预制体结构对炭／炭复合材料力学性能影响

四种用于制备炭／炭（C／C）复合材料的预制体，即1K发布叠层坯体（1#坯体），3K发布叠层坯体（4#坯体），发市 炭纸叠层坯体（2#坯体），特殊炭毡 发布叠层坯体（3#坯本），并探索了预制体结构对C／C复合材料力学性能影响．研究表明：用1#坯体制备的C／C复合材料弯曲强度最高，2#坏体制备的材料弯曲强度最低，随著炭纤维（CF）体积含量的增加，用四种坯体制备的材料弯曲强度增大。确定了弯曲强度的优化配方．     

Effect of preform architecture on the mechanical properties of 2D C/C composites prepared using rapid directional diffused CVI processes

The substrate architecture of carbon-carbon (C/C) composites has an effect on both the mechanical properties and the cost of the products. Four kinds of substrate materials, 1K and 3K plain carbon cloth, carbon paper, and carbon felt, were used in this study, and from them four different 2D preforms were produced, namely, 1K plain carbon cloth, carbon paper+1K plain carbon cloth, carbon felt+1K plain carbon cloth, 3K plain carbon cloth, using a spreading layer method. The preforms were densified using the rapid directional diffused CVI processes. A three-point bend test was used to investigate the influence of preform architecture on the flexural properties and microstructure of the C/C composites. The results show that all samples have an obvious pseudo-plastic fracture behaviour, and the macroscopic appearance of the bent fractured section shows as an Z shape. The samples prepared using 1K plain carbon cloth have a uniform microstructure, and consequently possess the highest flexural strength, while the composites produced from 3K plain carbon cloth possess the lowest value due to their poor microstructure and lower strength fibers. In general the flexural properties of the C/C composites are improved with an increase of the carbon fiber volume fraction in the preform. All the C/C composites manufactured from the four preforms fail by delamination when broken.     

Effects of surface structure unit of 2D needled carbon fiber preform on the microstructure and ablation properties of C/C-ZrC-SiC composites

To investigate the effects of different structure units on the ablation properties of C/C-ZrC-SiC composites produced from 2D needled carbon fiber preforms as reinforcements, non-woven layer, short-cut fiber web and the surface of laminated layers of the composites were ablated by oxyacetylene flame respectively. Results showed that the formation ability of surface protective layer and the fiber orientation were the key factors, determining ablation properties of different structure units. Short-cut fiber web presented the best ablation resistance due to the forming of compactly integrated ZrO₂ self-protection coating because of its sufficient ceramic content. However, only scattered oxide particles formed on the ablated surface of non-woven layer, which resulted in serious erosion of carbon fibers and carbon matrices, leading to the poor ablation resistance. Compared with the non-woven layer perpendicular to the flame, the anti-ablation property was even worse when it paralleled to the flame.     

Optimization Study of C/SiC Threaded Joints

The influences of fiber preform structure and thread engagement length on the mechanical properties of Carbon fiber reinforced silicon carbide matrix (C/SiC) threaded joints were studied. The results show that stacking 3K carbon fiber cloth followed by stitching is a good preform for preparing a C/SiC nut because of its high bearing ability. Stacking 1K carbon fiber cloth followed by stitching is a preferred preform to prepare a C/SiC bolt, and its minimum thread engagement length resulting in bolt rupture instead of thread spalling failure is 4 mm, which is obviously smaller than those of other bolts.     

Thermophysical properties of carbon/carbon composites and physical mechanism of thermal expansion and thermal conductivity

Five different carbon/carbon composites (C/C) have been prepared and their thermophysical properties studied. These were three needled carbon felts impregnated with pyrocarbons (PyC) of different microstructures, chopped fibers/resin carbon + PyC, and carbon cloth/PyC. The results show that the X-Y direction thermal expansion coefficient (CTE) is negative in the range 0-100 °C with values ranging from −0.29 to −0.85 × 10⁻⁶/K. In the range 0-900 °C, their CTE is also very low, and the CTE vs. T curves have almost the same slope. In the same temperature range composites prepared using chopped fibers show the smallest CTE values and those using the felts show the highest. The microstructure of the PyC has no obvious effect on the CTE for composites with the same preform architecture. Their expansion is mainly caused by atomic vibration, pore shrinkage and volatilization of water. However, the PyC structure has a large effect on thermal conductivity (TC) with rough laminar PyC giving the highest value and isotropic PyC giving the lowest. All five composites have a high TC, and values in the X-Y direction (25.6-174 W/m K) are much larger than in the Z direction (3.5-50 W/m K). Heat transmission in these composites is by phonon interaction and is related to the preform and PyC structures.     

针刺用炭布／网胎复合织物单层增厚及变形性分析

炭布／网胎复合织物是C／C复合材料针刺预制体的一种重要原料。本文研究了针刺后不同种类炭布／网胎复合织物的单层增厚及针刺变形性。单层增厚与针刺后复合织物的结构、织物的厚度均匀性和针刺密度有关。针刺后复合织物的结构为“销钉”结构,织物的厚度均匀性影响Z向纤维的引入量,针刺密度是影响单层增厚最为显著的因素。针刺密度为20针／cm^2时,预氧丝网胎复合织物的单层增厚小于0．2mm,增厚百分比在4％～25％之间;针刺密度为32针／cm^2时,炭纤维网胎复合织物的单层增厚在0．14mm-0．23mm之间,增厚百分比在16％～34％之间。不同种类炭布／网胎复合织物的整体变形性较为相似,针刺变形性与炭布的结构有关。