热处理温度对炭/炭复合材料性能的影响

利用热梯度化学气相沉积工艺制备了炭／炭复合材料,研究了热处理温度对炭／炭复合材料石墨化度、硬度、抗弯强度和摩擦性能的影响。结果表明：石墨化度随着热处理温度的升高而增大,炭,炭复合材料石墨化的能垒在2200℃附近;炭／炭复合材料的抗弯强度随着热处理温度的升高,先升高后降低,当热处理温度是2000℃时,所得材料的抗弯强度最高;炭／炭复合材料的硬度和摩擦系数随着热处理温度的升高而降低。     

不同热处理温度下炭/炭复合材料的制动摩擦性能

在MM - 10 0 0摩擦试验机上 ,对一种针刺毡结构的炭 /炭 (C/C)复合材料在不同热处理温度下的摩擦磨损性能进行了测试 ,并对摩擦表面进行了光学形貌观察 ;采用X射线衍射技术测试了其在不同热处理温度下的石墨化度 ,并对石墨化度与材料的摩擦性能之间的关系进行了探讨。结果表明 :随着热处理温度升高 ,针刺毡结构的炭 /炭复合材料的石墨化度提高 ,摩擦磨损性能也相应发生变化 ,即摩擦因数开始随热处理温度升高而增大 ,到 2 30 0℃时出现峰值 ,线性磨损和质量磨损则在 2 2 0 0℃时出现峰值 ,氧化磨损则随热处理温度升高而下降。石墨化度对材料的摩擦磨损性能有一定影响 ,合理控制石墨化度可以得到理想性能的材料 ,对本研究所用的C/C复合材料其最佳的热处理温度为 2 30 0℃。     

热膨胀性能对炭/炭复合材料在制动摩擦过程中热应力场的影响

测量以纯树脂炭、粗糙层热解炭和光滑层热解炭为基体的3种炭/炭复合材料的热膨胀系数,并采用有限元分析软件,模拟这3种炭,炭复合材料在飞机正常着陆能量条件下的热应力场,研究热膨胀系数对炭,炭复合材料热应力场及其摩擦性能的影响.结果表明:3种炭/炭复合材料在z方向上的热膨胀系数大于在X和y方向的,且热膨胀系数均随着温度的升高而逐渐增大,其中,基体为粗糙层热解炭的炭/炭复合材料的热膨胀系数最小,纯树脂炭试样的次之,光滑层热解炭试样的最大;在制动过程中,炭/炭复合材料摩擦表面产生的热应力与材料的热膨胀系数相关,材料的热膨胀系数越大,产生的热应力越大;过大的热应力使纯树脂炭试样具有相对稳定的摩擦曲线,在较大热应力的作用下,光滑层热解炭试样的摩擦曲线不稳定,影响其摩擦性能.     

炭／炭复合材料导热系数影响因素的研究

研究了影响炭／炭复合材料导热系数的主要因素：炭纤维取向，热处理温度和CVD热解炭的结构，结果表明，在炭／炭复合材料中，影响炭／炭复合材料导热系数的主要因素是CVD热解炭结构；以RL结构为主的CVD热解炭，导热系数高，热处理温度对材料导热系数的影响不及CVD热解炭的微观结构对其的影响。     

原位生长碳纳米管对炭/炭复合材料导热性能的影响

以炭纤维表面原位生长有碳纳米管(Carbon nanotubes,CNTs)的针刺毡体作为前驱体制备出生长有CNTs的炭/炭复合材料,并与在同样工艺条件下通过致密化最终热处理得到的纯炭/炭复合材料进行对比.结果表明,在密度几乎相同的情况下,生长有CNTs的炭/炭复合材料的室温Z轴热导率约为11.10 W/(m·K),几乎为纯炭/炭复合材料的室温Z轴热导率(6.28 W/(m·K))的2倍,其原因可能在于CNTs可以有效改善炭纤维和热解炭之间的界面特性,明显减少炭/炭复合材料中纤维和热解炭界面处周裂纹的出现,还可以诱导热解炭形成一种拥有更高导热率更易石墨化的粗糙结构.     

炭/炭复合材料石墨化度的XRD均峰位法测定

采用XRD平均峰位法测定了4种C／C复合材料的石墨化度。研究结果表明：用平均峰位法测定C／C复合材料的石墨化度具有简便可靠、区分度高的优点。当C／C复合材料中炭纤维的含量低于基体炭含量时，难石墨化的炭纤维对C／C复合材料XRD谱线低角度一侧的线形有一定影响，但对最终的测量结果影响不大。     

炭/炭复合材料航空刹车副的湿态摩擦性能

对两种不同的炭/炭复合材料湿态下的摩擦磨损性能进行对比分析。结果表明:具有粗糙层热解炭的炭/炭刹车副由于其晶格结构较为完善,生长组织择优取向度和各向异性度均高于含有光滑层结构热解炭的炭/炭刹车副。前者的石墨化度及可石墨化能力均大于后者,由于前者的表面缺陷较少,所吸附的水分子较少,因而在湿态下刹车时,其刹车力矩将很快恢复到正常干态刹车时的力矩水平,对环境的适应能力大于光滑层结构的炭/炭刹车副。     

密封用炭/炭复合材料的摩擦磨损性能

针对液体火箭发动机涡轮泵密封件磨损量较大问题,在MVF-1A多功能立式摩擦磨损试验机上,以GCr15钢环为对偶件,研究低载荷高线速度(12N,2.25m/s)以及高载荷低线速度(50N,1.25m/s)工况条件下热处理温度不同时(2 250、2 400和2 500℃)对炭/炭(C/C)密封材料摩擦磨损性能的影响,采用扫描电镜观察摩擦表面形貌,利用能谱仪确定摩擦表面元素组成。结果表明:低温(2 250℃)热处理材料石墨化度程度低,弯曲强度高,摩擦因数小,线性磨损量大;随着热处理温度的升高,材料石墨化程度升高、界面结合强度弱化,弯曲强度降低;当热处理温度升高到2 500℃后,材料表面易形成完整致密的磨屑膜,磨损机制由磨粒磨损转变为粘着磨损,摩擦因数大,线性磨损量低。此外,在高载荷条件下,适当增大线速度(1.50、1.88m/s),有利于降低摩擦因数及线性磨损量。由此可知,采用高温(2 500℃)热处理的C/C复合材料具有良好抗磨性能,可较好地满足密封件使用要求。     

结构类似的炭材料和C/C复合材料的滑动摩擦磨损行为

制备粗糙层热解炭(RL)和光滑层热解炭(SL)基体的C/C复合材料,测试该C/C复合材料与40Cr钢配副时的摩擦磨损行为,并对磨损表面进行SEM观察.对比研究高强石墨和光滑层结构的块状热解炭在相同条件下的滑动摩擦磨损行为.结果表明:PAN炭纤维改善C/C复合材料的摩擦磨损行为;在实验载荷范围内,与高强度石墨材料相比,含RL炭C/C复合材料的摩擦因数降低0.08～0.12;体积磨损量增幅降低;与热解炭试样相比,具有SL炭C/C复合材料的摩擦因数降低0.02～0.05,体积磨损量低0.2 mm~3左右;随着时间的延长,大部分C/C复合材料的摩擦因数基本相对稳定或呈小幅下降,而石墨、热解炭块的摩擦因数均呈不同幅度的上升;具有RL炭的C/C复合材料摩擦表面膜厚度随载荷增加而降低,具有SL炭的C/C复合材料摩擦表面较粗糙;高强石墨能形成较完整致密的摩擦膜,但磨粒磨损严重,磨屑易在摩擦膜边缘形成层状堆积;热解炭块摩擦表面磨屑堆积松散,有较多的孔洞以及热解炭层整体剥落的形貌.     

新型SiC-MoSi2/Al-O-Ti炭/炭抗氧化复合涂层的制备及其性能研究

采用包埋和涂刷法制备出一种新型的炭/炭复合材料抗氧化涂层,它由自愈合内涂层、热膨胀系数匹配过渡层、氧阻挡层三层复合而成.用SEM,XRD对它的组分和形貌进行了表征,同时测试了涂层在1 000,1 300和1 400℃下的抗氧化性能和抗热震性能.实验结果表明:该涂层能在1 400℃下有效保护炭/炭材料达50 h以上,经过...     

碳纤维表面生长纳米碳管及其增强的炭/炭复合材料

采用化学气相沉积工艺在碳纤维表面生长了纳米碳管,将此种碳纤维作为增强材料,以中间相沥青为基体炭前驱体采用浸渍炭化工艺制备了炭/炭复合材料.观察了所得复合材料断口的微观形貌,测试了抗弯强度及热物理性能.结果表明,碳纤维表面的纳米碳管可以有效地提高纤维与基体的粘结力,复合材料的抗弯性能提高了50%,而对复合材料的导热性能影响较小.     

Microstructure of carbon fiber preform and distribution of pyrolytic carbon by chemical vapor infiltration

The carbon/carbon composites were made by chemical vapor infiltration(CVI) with needled felt preform. The distribution of the pyrolytic carbon in the carbon fiber preform was studied by polarized light microscope (PLM) and scanning electronic microscope(SEM). The experimental results indicate that the amount of pyrolytic carbon deposited on the surface of chopped carbon fiber is more than that on the surface of long carbon fiber. The reason is the different porosity between the layer of chopped carbon fiber and long carbon fiber. The carbon precursor gas which passes through the part of chopped carbon fibers decomposes and deposits on the surface of chopped carbon fiber. The pyrolytic carbon on the surface of long carbon fibers is produced by the carbon precursor gas diffusing from the chopped fiber and the Z-d fiber. Uniform pore distribution and porosity in preform are necessary for producing C/C composites with high properties.     

核壳结构镍碳纳米胶囊和碳纤维的制备

以脱油沥青（Deoiled Asphalt）为碳源、二茂铁为催化剂,采用化学气相沉积法（CVD）制备碳纤维（CFs）,其裂解后的残渣经真空热处理制得含镍碳纳米胶囊（CNCs）。用场发射扫描电镜（FESEM）、高分辨透射电镜（HRTEM）、X射线衍射仪（XRD）和拉曼光谱（Raman）对产物进行表征。结果表明：碳纤维纯度较高,属中空结构,直径主要分布在200～500 nm范围内;含镍碳纳米胶囊为准球形核壳结构,核为金属镍,壳为石墨化碳,大小在5～30 nm范围,晶化程度较高,结构较完善。     

Double SiC coating on carbon/carbon composites against oxidation by a two-step method

To improve the oxidation resistance of C/C composites, a double SiC protective coating was prepared by a two-step technique. Firstly, the inner SiC layer was prepared by a pack cementation technique, and then an outer uniform and compact SiC coating was obtained by low pressure chemical vapor deposition. The microstructures and phase compositions of the coatings were characterized by SEM, EDS and XRD analyses. Oxidation behaviour of the SiC coated C/C composites was also investigated. It was found that the double SiC coating could protect C/C composites against oxidation at 1773 K in air for 178 h with a mass loss of 1.25%. The coated samples also underwent thermal shocks between 1773 K and room temperature 16 times. The mass loss of the coated C/C composites was only 2.74%. Double SiC layer structures were uniform and dense, and can suppress the generation of thermal stresses, facilitating an excellent anti-oxidation coating.     

Preparation and mechanical properties of carbon/carbon composites with high textured pyrolytic carbon matrix

Short carbon fiber felts with an initial porosity of 89.5% were deposited by isobaric, isothermal chemical vapor infiltration using natural gas as carbon source. The bulk density of the deposited carbon/carbon (C/C) composites was 1.89 g/cm³ after depositing for 150 h. The microstructure and mechanical properties of the C/C composites were studied by polarized light microscopy, X-ray diffraction, scanning electron microscopy and three-point bending test. The results reveal that high textured pyrolytic carbon is deposited as the matrix of the composites, whose crystalline thickness and graphitization degree highly increase after heat treatment. A distinct decrease of the flexural strength and modulus accompanied by the increase of the toughness of the C/C composites is found to be correlated with the structural changes in the composites during the heat treatment process.     

预浸涂对航空刹车副用C/C复合材料抗氧化涂层性能的影响

采用在C/C复合材料基体表面预先浸涂浸渍剂 ,再涂刷涂层并进行涂层固化处理的工艺方法 ,可制备出抗氧化性能良好的涂层。预浸涂处理可使C/C复合材料的起始氧化温度提高近 2 0 0℃。单独预浸涂以硼酸或TEOS为主的浸渍剂后 ,试样抗氧化效果不明显 ,而预浸涂以磷酸或磷酸 硼酸混合液为主的浸渍剂效果较好 ,90 0℃ ,2h静态氧化质量损失率分别为 0 .4 0 %和 0 .33%。并对以硼酸 ,磷酸和TEOS及其混合液为主的浸渍剂的抗氧化机理进行了分析和探讨     

Graphene-coated copper foam interlayer for brazing carbon/carbon composite and niobium

Problems such as poor structural integrity, inhomogeneous dispersion, and agglomeration of graphene in the brazing seam are typically encountered for graphene additives in a brazed joint interface. To resolve these problems, a plasma-enhanced chemical vapor deposition process was employed for in-situ preparation of a high-quality graphene-coated copper (Cu) foam composite interlayer prior to be applied for brazing carbon/carbon composite and niobium. The prepared graphene and the brazed joints were characterized via Raman spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The results revealed that graphene was evenly distributed in the brazing seam with the help of the Cu foam, which was characterized by interconnected porosity. Simultaneously, the excellent chemical inertia of graphene inhibited the collapse of the Cu foam, based on which the thermal residual stress in the joint was effectively mitigated due to the synergistic reinforcement effect of the Cu foam (with good plastic deformation capacity) and graphene (with extremely low coefficient of linear expansion). This effect led to significant improvement in the average shear strength of the joint.     

Equilibration of plain carbon and alloy steels with endothermic carburizing atmospheres: Part I. Activity of carbon in plain carbon steels

Experimental data on the activity of carbon in commercial plain carbon steel, AISI type 1010, common shim-stock material, at 871 °C, 927 °C, 1000 °C, and 1038 °C, equilibrated with common endothermic carburizing atmospheres, were found to be generally in agreement at relatively high carbon concentrations with previously published data on pure iron equilibrated with CO-CO₂ mixtures. However, noticeable differences were found at low carbon concentrations. The carbon contents of type 1010 steel were generally higher compared to those of previously published data regarding pure iron except at very high activities of carbon. The carbon contents of type 1010 steel foil specimens by weight gain were generally higher than or equal to those chemically analyzed; however, they corresponded with each other within 0.02 wt.% except at very low carbon potentials.     

C/C复合材料航空刹车副表面防氧化涂料的研制

以磷酸,磷酸盐,ＳｉＣ,ＳｉＯ２,Ｂ４Ｃ和含硼化合物等为原料研制了以硅、硼化合物为主的多组分陶瓷混合物涂料。采用该涂料以刷涂的方式制备的Ｃ／Ｃ复合材料复合涂层具有显著的防氧化效果。研究表明,涂覆有涂层的Ｃ／Ｃ复合材料试样在９００℃氧化１０ｈ后,其氧化损失率为１０．３７％;试样在空气中９００℃,３ｍｉｎ＝室温,２ｍｉｎ急冷急热,如此在１０ｈ内循环１００次后,氧化损失率为８．４１％,涂层与基体结合牢固