高性能炭/炭刹车盘的纤维分布与基体炭特性

炭/炭刹车盘是炭/炭(C/C)复合材料制成品中制造难度最大的一种,除了对其基体炭的结构有特殊要求外,炭纤维预制体的结构也是影响其使用性能的一个关键性因素.该文作者采用先进检测设备对一些高性能炭/炭刹车盘进行了详细的检测、分析.结果显示:高性能炭/炭刹车盘的预制体是由叠层厚度约为0.5 mm、重复单元为…60°/90°/60°/90°…的连续长炭纤维层和厚度约为0.5 mm的短纤维层经针刺而成,其针刺密度约为2.2 hole/mm2.该刹车盘的CVD炭为RL结构炭,并且炭纤维间结合紧密,炭刹车盘的石墨化度高达89.2%.     

制动速度与压力对飞机炭刹车盘摩擦磨损性能的影响

采用HJDS-Ⅱ惯性台在各种制动速度/压力及外场装机使用的条件下,对西安超码科技公司采用自主创新专利技术生产的Chaoma B757,Chaoma A320炭刹车盘与Dunlop公司的B757,以及Messier-Bugatti公司的A320Sepcarb?ⅢOR炭刹车盘的摩擦因数、平均力矩和磨损率进行对比试验。结果表明:4种类型炭刹车盘材料的能量、力矩均随制动速度和制动压力增加而增大;摩擦因数在低速阶段均出现低能峰值特性,然后随着制动速度与压力增加呈降低趋势。ChaomaB757,A320炭刹车盘凸显2个特色:在飞机中止起飞能量下制动压力比国外原件低25%,摩擦因数比国外原件高25%～29%;B757炭刹车盘的装机应用的最长使用寿命达到2823~3289次起落,与国外B757原件的使用寿命相当,凸显出优异的低磨损率特色。     

氮气、空气条件下炭/炭复合材料的摩擦磨损性能

在MM-1000型摩擦试验机上,对炭/炭复合材料分别在氮气和空气中模拟正常着陆能量条件下的摩擦磨损行为进行测试。结果表明:在氮气中,炭/炭复合材料的摩擦因数较高,达到0.32～0.4,磨损率较低,质量磨损率为18 mg/次,线性磨损率为1.4μm/次;在空气中,材料的摩擦因数较低,为0.2～0.3,但磨损率较高,质量磨损率为48 mg/次,线性磨损率为3.8μm/次。磨损表面及磨屑的SEM形貌表明:在空气中,材料摩擦表面易形成炭纤维、基体炭相互脱离的磨屑,其主要磨损机制为氧化磨损;在氮气中,则有纤维与基体炭连接良好、大尺寸的磨屑出现,主要磨损机制为磨粒磨损和粘着磨损。     

基体炭含量对C/C复合材料滑动摩擦磨损行为的影响

在M2000型摩擦试验机上,以表面镀Cr的40Cr钢为配副,测试了基体炭分别为光滑层热解炭(SL)、树脂炭(RC)和热解树脂炭(SL/RC)的3种C/C复合材料摩擦磨损行为.结果表明:随载荷增加,基体炭为全SL炭的材料A摩擦因数变化小,在0.117～0.105之间;全RC炭的材料B波动最大,在0.156～0.123之间;基体炭中SL炭质量分数为48.9%、RC炭质量分数为20.2%的材料C的摩擦因数波动幅度接近于材料A,在0.120～0.110之间.材料C的体积磨损最小,在0.191～0.620 mm3之间.随时间延长,材料A、C的摩擦因数稳定,材料B的下降幅度最大.SEM观察表明,随载荷增加,材料B摩擦表面逐渐致密、完整,材料C摩擦表面的纤维磨损现象加重.     

连续高温制动条件下颗粒增强铁基复合材料的摩擦磨损性能

采用粉末冶金烧结工艺制备了颗粒增强铁基复合材料,研究了颗粒增强铁基复合材料在连续高温制动条件下的摩擦磨损性能。通过扫描电子显微镜观察、能谱分析和热电偶测温等方法研究了摩擦系数、力矩、稳定系数和磨损率的变化规律,并分析相应磨损机理。结果表明：随接合次数增加,摩擦副温度显著提高,在表面形成多层结构的摩擦膜,可有效减少黏着倾向和犁沟效应,因此平均摩擦系数和平均力矩呈先上升后下降趋势,稳定系数下降。前期摩擦副接合以黏着磨损和磨粒磨损为主,磨损率较高;后期接合摩擦膜起到保护作用,以摩擦膜层间和边缘的疲劳磨损为主,磨损率较低。     

炭/炭复合材料机轮刹车盘磨削加工方案分析

以炭／炭复合材料飞机机轮刹车盘为例，介绍了冼俄复合材料坯体的组成及机械特性、表面质量要求。根据该材料的特性和产品要求。制定了产品最终机加工磨削加工方案。同时，采用周边固定法。对工件的受力情况作了分析，对用此种固定法磨削加工的产品质量作了评价，结果表明，此种磨削工艺完全满足生产的要求。     

热解碳结构对炭/炭复合材料摩擦磨损性能的影响

通过控制化学气相沉积(CVD)工艺条件,得到粗糙层、光滑层、过渡层等几种具有不同微观结构的热解碳。金相观察、摩擦磨损性能的测试结果表明:热解碳的微观结构对炭/炭复合材料的摩擦磨损性能有重大影响;粗糙层结构的炭/炭复合材料摩擦因数高,热稳定性好,是一种优良的摩擦材料;光滑层结构的炭/炭复合材料摩擦因数低,磨损小,可以用作耐磨材料。     

飞机炭刹车盘的制动摩擦性能

研究了某种针刺毡结构的C/C复合材料刹车盘在不同能量、压力及湿态环境下的摩擦磨损性能,结果表明:该种材料具有稳定的摩擦性能和重复性,刹车力矩平稳,且能载水平高,磨损小;湿态环境下平均动摩擦系数降低,但随着压力的增大,这种影响减小。     

飞机炭刹车盘刹车压力-刹车力矩特性研究

飞机炭刹车盘在压力系统提供的压力作用下,动盘和静盘相互摩擦,产生摩擦力矩。刹车压力的大小对飞机炭刹车盘的摩擦性能具有较大影响。通过对3套炭刹车盘在不同压力状态下的刹车试验,对整套炭刹车盘的摩擦磨损性能进行系统研究,分析飞机炭刹车盘在可用刹车压力条件下,摩擦性能参数的变化规律。结果表明,超码研制的A320系列飞机炭刹车盘在整个刹车压力区间内,摩擦因数、平均力矩等性能指标均在国外原件的性能范围内,与国外原件具有等效的刹车性能。     

炭纤维增强树脂炭复合材料的烧蚀性能

采用等离子烧蚀方法研究了炭纤维增强树脂炭复合材料的烧蚀性能,并对其烧蚀表面形貌进行扫描电镜现察。结果表明,材料取向对其烧蚀性能有很大影响。     

化学镀碳纤维增强羟基磷灰石复合材料的性能

通过化学镀方法,在碳纤维表面分别镀上Ni和Cu+Ni镀层,以这种表面改性碳纤维与羟基磷灰石陶瓷复合,制备表面改性碳纤维增韧增强羟基磷灰石复合材料,研究各种碳纤维的含量对复合材料的抗弯强度、断裂韧度、尺寸变化率和孔隙率的影响。结果表明,表面改性碳纤维可以显著提高材料的性能,尤其是铜镍复合镀碳纤维的效果更好,其断裂韧度可达基体断裂韧度的2.5倍,抗弯强度可达基体抗弯强度的3.4倍,增韧增强后的复合材料的尺寸和孔隙率变化不大。     

碳纤维表面状态及其对复合材料剪切性能的影响

采用X射线衍射仪和扫描电镜观察了碳纤维表面的微观结构以及复合材料的截面形貌,分析了进口碳纤维和国产碳纤维的表面状态差异,以及此差异对碳纤维复合材料进行层间剪切强度(ILSS)的影响.结果表明进口碳纤维表面粗糙度更大,沟槽深度和宽度均大于国产碳纤维.在树脂基复合材料中,进口碳纤维与树脂基体结合更为紧密,固化后形成制件的孔隙率更低,其室温和高温层间剪切强度都高于相应国产碳纤维体系.因此,尽管表面处理会对碳纤维表面造成一定的影响,但处理后得到的高粗糙度表面是纤维在复合材料中形成较强界面的根本原因.     

HNO_3氧化改性对国产PAN基炭纤维表面成分和组织结构的影响

采用HNO3对国产PAN基炭纤维进行表面改性处理。采用氧氮氢联测仪、XPS、FTIR、Raman、SEM检测改性后炭纤维表面活性基团和微观结构的变化。结果表明:经55℃氧化处理后,纤维质量减小;而经80℃和100℃处理后,纤维质量增加。氧化处理后,纤维整体和表面的氧含量都增加,整体的氧含量明显低于表面,而增幅却高于表面。在氧化过程中,—OH、C—O、C=O、COOR及吡啶型氮、四价氮、—NO2的生成与转变同时发生,形成了低活性基团向高活性基团转变的动态过程,且随氧化温度升高或时间延长,纤维表面无序度降低。     

Wear and friction behavior of metal impregnated microporous carbon composites

Metal-matrix composites have been prepared by pressure-infiltration casting of copper-base alloy melts into microporous carbon preforms. The carbon preforms contained varying proportions of amorphous carbon and graphite. Load dependence of the wear and friction behavior of the composite pins has been examined under ambient conditions against cast-iron plates, using a pin-on-plate reciprocating wear tester. The wear resistance of the composite is significantly improved, as compared with the base alloy. Contrary to the normally expected behavior, the addition of graphite to the amorphous carbon does not reduce the friction coefficient, especially at high loads. The wear and friction behavior of the composites is very sensitive to the size and distribution of the microstructural constituents.     

Tensile and fatigue behavior of Al-based metal matrix composites reinforced with continuous carbon or alumina fibers: Part I. Quasi-unidirectional composites

The thermomechanical (dilatometric, tensile, and fatigue) behavior of Al-based metal matrix composites (MMCs) is investigated. These composites are reinforced by quasi-unidirectional (quasi-UD) woven fabric preforms with 90 pct of continuous fibers in the longitudinal direction and 10 pct in the transverse direction. The two composite systems investigated feature a highly ductile matrix (AU2: Al-2Cu wt pct) with a strongly bonded fiber-matrix interface (N610 alumina fibers) and an alloyed, high-strength matrix (A357: Al-7Si-0.6Mg wt pct) with a weak fiber-matrix interface (K139 carbon fibers). Microstructural investigation of the tested specimens has permitted identification of the specific characteristics of these composites: undulation of the longitudinal bundles, presence of the straight transverse bundles, interply shearing, and role of brittle phases. Moreover, simple semiquantitative models (e.g., interply shearing) have enabled explanation of the specific mechanical behavior of these quasi-UD composites, which exhibit high tensile and fatigue strengths, as compared with the corresponding pure UD composites. Knowledge of the specific characteristics and mechanical behavior of these quasi-UD composites will facilitate the further investigation of the (0, ±45, 90 deg) quasi-UD laminates (Part II). At a more theoretical viewpoint, the specific geometry and behavior of these quasi-UD composites allows exacerbation of fatigue mechanisms, even more intense than in “model” composites.     

Tensile and fatigue behavior of Al-based metal matrix composites reinforced with continuous carbon or alumina fibers: Part II. Quasi-unidirectional composite cross-ply laminates

The mechanical behavior (tension, fatigue, and notch sensitivity) of Al-based metal matrix composite (MMC) cross-ply laminates is investigated. The two selected laminates, K139/A357 and N610/AU2, are reinforced by continuous K139 (carbon) or N610 (alumina) fibers. These multiplies consist in the stacking of (quasi-unidirectional) quasi-UD preforms oriented at 0, ±45, and 90 deg, the thermomechanical behavior of the corresponding quasi-UD composites being reported independently (Part I). The investigated cross-ply laminates exhibit attractive static and cyclic performances and a low notch (circular hole) sensitivity. High-resolution microfractography has led to a better understanding of the fracture mechanisms of these materials. In this respect, the role of the transverse bundles is dominant in the tensile and fatigue failure of both laminates. However, the failure surfaces are completely different: long fiber pullout in the K139/A357 laminate and much more planar areas in the N610/AU2 laminate. Due to the rather low notch sensitivity, a large portion of the specimen section was already highly damaged during a non-negligible part of the fatigue life: debonded interfaces in the K139/A357 laminate and multicracked and “crumbled” matrix in the N610/AU2 laminate. These mechanisms are in good agreement with the weak interface in the first case and the very low yield stress of the AU2 matrix, much lower than the fatigue limit of the N610/AU2 laminate, in the second case. Moreover, compared to the quasi-UD composites, the stress concentration around the notch allows further exacerbation of the fatigue mechanisms, much more intense than that attained in “model” composites.     

Creep behavior of fiber reinforced metal matrix composites

A theoretical model of the creep behavior of metal matrix composites having strong fiber-matrix interfaces is described in terms of creep parameters of the matrix and fibers. The available experimental data, obtained from the unidirectionally solidified aluminum-nickel eutectic containing 10 vol pct Al₃Ni fibers, are in good agreement with the theoretical model. The creep activation energy of the composite is described in terms of the creep activation energy of fibers and the matrix. The experimentally de-termined data of (Co, Cr)-(Co, Cr)₇C₃ and Al-Al₃Ni eutectics are in agreement with those values as predicted.     

Creep behavior of fiber reinforced metal matrix composites

A theoretical model of the creep behavior of metal matrix composites having strong fiber-matrix interfaces is described in terms of creep parameters of the matrix and fibers. The available experimental data, obtained from the unidirectionally solidified aluminum-nickel eutectic containing 10 vol pct Al₃Ni fibers, are in good agreement with the theoretical model. The creep activation energy of the composite is described in terms of the creep activation energy of fibers and the matrix. The experimentally de-termined data of (Co, Cr)-(Co, Cr)₇C₃ and Al-Al₃Ni eutectics are in agreement with those values as predicted. Formerly a Visiting Scholar, Materials Department, University of California, Los Angeles.