Tribological properties and thermal-stress analysis of C/C-SiC composites during braking

The tribological properties and thermal-stress behaviors of C/C-SiC composites during braking were investigated aiming to simulate braking tests of high-speed trains. The temperature and structural fields of C/C-SiC composites during braking were fully coupled and simulated with ANSYS software. The results of tribological tests indicated that the C/C-SiC composites showed excellent static friction coefficient (0.68) and dynamic friction coefficient (average value of 0.36). The highest temperature on friction surface was 445℃. The simulated temperature field showed that the highest temperature which appeared on the friction surface during braking was about 463℃. Analysis regarding thermal-stress field showed that the highest thermal-stress on friction surface was 11.5 MPa. The temperature and thermal-stress distributions on friction surface during braking showed the same tendency.

Preparation and properties of C/C-SiC brake composites fabricated by warm compacted-in situ reaction

Carbon fibre reinforced carbon and silicon carbide dual matrix composites（C/C-SiC） were fabricated by the warm compacted-in situ reaction.The microstructure,mechanical properties,tribological properties,and wear mechanism of C/C-SiC composites at different brake speeds were investigated.The results indicate that the composites are composed of 58wt%C,37wt%SiC,and 5wt%Si.The density and open porosity are 2.0 g.cm^（-3） and 10%,respectively.The C/C-SiC brake composites exhibit good mechanical properties.The flexural strength can reach up to 160 MPa,and the impact strength can reach 2.5 kJ.m^（-2）.The C/C-SiC brake composites show excellent tribological performances.The friction coefficient is between 0.57 and 0.67 at the brake speeds from 8 to 24 m·s^（-1）.The brake is stable,and the wear rate is less than 2.02×10^（-6） cm^3·J^（-1）.These results show that the C/C-SiC brake composites are the promising candidates for advanced brake and clutch systems.

Wet friction performance of C/C-SiC composites prepared by new processing route

C/C-SiC composites with SiC island distribution Were prepared via a new processing route. The fabrication process mainly included silicon infiltration by ultrasonic vibration, chemical vapor deposition （CVD）, siliconizing, liquid phase impregnation and carbonization. The wear and friction properties were tested by an MM-1000 wet friction machine. The results show that SiC phases are mainly distributed between carbon fibers and pyrocarbons as well as among the pryoearbons. The dynamic friction coefficient of the composites decreases gradually from 0.126 to 0.088 with the increase of the surface pressure from 0.5 to 2.5 MPa at the same rotary speed. Furthermore, under the constant surface pressure, the dynamic friction coefficient increases from 0.114 to 0.126 with the increase of the rotary speed from 1 500 to 2 500 r/min. However, the coefficient decreases to 0.104 when the rotary speed exceeds 4 500 r/min. During the friction process, the friction coefficient of C/C-SiC composite is between 0.088 and 0.126, and the wear value is zero after 300 times brake testing.

Oxidation Behavior of C/C-SiC Gradient Matrix Composites

Oxidation behavior of C/C-SiC gradient matrix composites and C/C composites were compared in stationary air. The results show that oxidation threshold of C-SiC materials increases with the amount of SiC particles in the codeposition matrix. Oxidation rate of C/C-SiC gradient matrix composites is significantly lower than that of C/C material. The micro-oxidation process was observed by SEM.

The influence of ablation products on the ablation resistance of C/C-SiC composites and the growth mechanism of SiO_2 nanowires

Ablation under oxyacetylene torch with heat flux of 4186.8（10%kW/m2 for 20 s was performed to evaluate the ablation resistance of C/C-SiC composites fabricated by chemical vapor infiltration（CVI） combined with liquid silicon infiltration（LSI） process.The results indicated that C/C-SiC composites present a better ablation resistance than C/C composites without doped SiC.The doped SiC and the ablation products SiO2 derived from it play key roles in ablation process.Bulk quantities of SiO2 nanowires with diameter of 80 nm-150 nm and length of tens microns were observed on the surface of specimens after ablation.The growth mechanism of the SiO_2 nanowires was interpreted with a developed vapor-liquid-solid（VLS） driven by the temperature gradient.

Friction and Wear Behaviors of C/C-SiC Composites under Water Lubricated Conditions

C/C-SiC composites have the potentiality to be applied in shield pumps of nuclear reactors as the bearing material because of their low density,good mechanical properties and excellent tribological properties.The C/C-SiC composites are fabricated via reactive melt infiltration(RMI)using silicon liquid infiltrated in C/C matrix composites.Friction and wear behaviors of C/C-SiC composites under water lubricated conditions are investigated using the block-on-ring test at room temperature,and compared with those of the resin graphite which is used as the bearing material in shield pumps at present.In addition,friction and wear mechanisms of C/C-SiC composites under water lubricated conditions have been discussed.Results show that tensile strengths of C/C-SiC composites are 150210 MPa,and compressive strengths are 403536 MPa.Friction and wear behaviors of C/C-SiC composites are closely related to the load and the speed.The time to reach a stable friction status decreases with the increase of the speed.Though the friction coefficient of C/C-SiC composites under water lubricated conditions is slightly higher than that of graphite,the wear rate of C/C-SiC composites is much lower,which suggests that the C/C-SiC composites can sustain a longer life during operation.

Reciprocating sliding tribology of brake oil treated carbon fiber reinforced ceramic matrix composites

The effect of brake oil on sliding behavior of carbon/carbon(C/C) and carbon/carbon-silicon carbide(C/C-SiC) composites was investigated with the variation of laminate orientation and surface conformity. The partial and low conformity contacts with the normal and parallel orientations of laminates were considered. The normal load was varied from 50 to 90 N in a step of 10 N. The friction and wear behavior was investigated under reciprocating sliding conditions. The results showed that friction coefficient and wear loss of composites with normal orientation of laminates were larger as compared to those of composites with parallel orientation of laminates. C/C composites with normal orientation of laminates yielded the highest value of friction coefficient. Wear loss decreased by a maximum of 78%, and friction coefficient decreased by a maximum of 49% in low conformity contacts as compared to partial conformity contacts. The presence of brake oil reduced the adhesion tendency of compacted wear debris because the formation of friction film was difficult, and thus, friction behavior was affected. The wear debris retention between the contact surfaces due to confined area motion in reciprocating sliding depicted the tribological behavior.

Carbon-fiber-reinforced silicon carbide composites prepared by precursor pyrolysis-hot pressing

The Cf/SiC composites were prepared by precursor conversion-hot pressing sintering with AIN and Y2Os as additives. The effects of sintering temperature and additives on the microstructures and properties of the composites were investigated. The composite sintered at as low as 1 75O℃ already showed higher density and better mechanical properties, which was mainly attributed to the liquid-phase-sintering and the formation of the AIN-SiC solid solution. With increasing the sintering temperature to 1 800 ℃, the flexural strength and fracture toughness of the composite were substantially improved up to 691. 6 MPa and 2O. 7 MPa’ m1/2 respectively in spite of the slightly elevated density, and the composite exhibited "tough" failure. Despite the improved density, the composite sintered at 1 85O℃ displayed brittle failure, which mainly attributed to the strongly bonded fiber/matrix interface and the degradation of the properties of the fibers.

Effect of fiber characteristics on fracture behavior of C_f/SiC composites

C f/SiC composites were prepared by precursor pyrolysis hot pressing, and the effect of fiber characteristics on the fracture behavior of the composites was investigated. Because the heat treatment temperature of fiber T300 (below 1?500?℃) was much lower than that of fiber M40JB (over 2?000?℃), fiber T300 had lower degree of graphitization and consisted of more impurities compared with fiber M40JB, suggesting that T300 exhibits higher chemical activity. As a result, the composite with T300 showed a brittle fracture behavior, which is mainly ascribed to a strongly bonded fiber/matrix interface as well as the degradation of fibers during the preparation of the composite. However, the composite with M40JB exhibits a tough fracture behavior, which is primarily attributed to a weakly bonded fiber/matrix interface and higher strength retention of the fibers.

Cf/SiC复合材料铣削加工过程仿真分析及试验研究

针对Cf/SiC复合材料铣削加工过程中刀具磨损快、加工效率低、加工工艺优化试验成本高等问题,开展Cf/SiC复合材料三维铣削仿真分析及试验研究。基于ABAQUS软件建立Cf/SiC复合材料三维铣削加工仿真有限元模型,预测加工过程中的铣削力,通过试验验证该模型的正确性。对比仿真预测的理论值和试验测得的实际值发现二者的平均误差仅为15%,所获取的一组较优的加工参数为Cf/SiC复合材料铣削加工参数优化提供了理论依据。

(C-SiC)f/C复合材料的烧蚀性能

将SiC纤维毡与C纤维毡交替层叠,通过针刺工艺制备(C-SiC)_f/C预制体,采用化学气相渗透与前驱体浸渍裂解复合工艺(CVI+PIP)制备(C-SiC)_f/C复合材料,研究(C-SiC)_f/C复合材料H_2-O_2焰烧蚀性能。利用SEM、EDS和XRD对烧蚀前后材料的微观结构和物相组成进行分析,探讨材料抗烧蚀机理。结果表明:(C-SiC)_f/C复合材料表现出更优异的耐烧蚀性能。烧蚀750 s后,(C-SiC)_f/C复合材料的线烧蚀率为1.88mm/s,质量烧蚀率为2.16 mg/s。与C/C复合材料相比,其线烧蚀率降低了64.5%,质量烧蚀率降低了73.5%;SiC纤维毡在烧蚀中心区表面形成的网络状保护膜可以有效抵御高温热流对材料的破坏;在烧蚀过渡区和烧蚀边缘区形成的熔融Si O2能够弥合材料的裂纹、孔洞等缺陷,阻挡氧化性气氛进入材料内部,使材料表现出优异的抗烧蚀性能。

Na2FePO4F/C composite synthesized via a simple solid state route for lithium-ion batteries

Using low-cost FePO4·2H2O as iron source,Na2FePO4F/C composite is prepared by alcohol-assisted ball milling and solid-state reaction method.The XRD pattern of Na2FePO4F/C composite demonstrates sharp peaks,indicating high crystalline and phase purity.The SEM and TEM images reveal that diameter of the spherical-like Na2FePO4F/C particles ranges from 50 to 300 nm,and HRTEM image shows that the surface of Na2FePO4F/C composite is uniformly coated by carbon layer with a average thickness of about 3.6 nm.The carbon coating constrains the growth of the particles and effectively reduces the agglomeration of nanoparticles.Using lithium metal as anode,the composite delivers a discharge capacities of 102.8,96.4 and 90.3 mA·h/g at rates of 0.5C,1C and 2C,respectively.After 100 cycles at 0.5C,a discharge capacity of 98.9 mA·h/g is maintained with capacity retention of 96.2%.The Li+diffusion coefficient(D)of Na2FePO4F/C composite is calculated as 1.71×10^–9 cm^2/s.This study reveals that the simple solid state reaction could be a practical and effective synthetic route for the industrial production of Na2FePO4F/C material.

C_f/SiC制备过程中纤维热应力损伤研究

采用束丝碳纤维和聚碳硅烷先驱体浸渍裂解工艺制成 Cf/ Si C丝束 ,并进行了分析表征 ,研究了其中的纤维受损情况。实验结果表明 ,由于先驱体聚碳硅烷在浸渍裂解时倾向于以纤维为依托进行热解 ,并且其中较多量的氧及杂质的存在将对纤维造成损伤 ,因而会形成较强的纤维基体界面 ;

偏磷酸铝粘结剂在真空液相浸渗制备C_f/Al复合材料中的应用研究

采用真空压力浸渗工艺 ,以高强高模碳纤维M4 0J增强AlMg5为研究对象 ,研究了预制件抗压强度提高技术和高温粘结剂偏磷酸铝对复合材料中纤维平直度、复合材料性能的影响。结果表明 ,预制件中偏磷酸铝的加入使复合材料中纤维的平直度及分布的均匀性提高 ,用P Al 15∶1、浓度为 10wt%偏磷酸铝溶液处理后的预制件经真空液相浸渗后制得的复合材料 ,纤维不仅保持了较好的平直度 ,而且弯曲强度比未经粘结剂处理的提高近 10 2 %左右 ,达到5 35MPa。

偏磷酸铝在C_f/AL复合材料中的应用

以高模高强石墨纤维Ｍ４０Ｊ增强铝基复合材料为研究对象，研究了真空液相压渗工艺中，偏磷酸铝粘接剂对纤维预制件抗压性能及复合材料力学性能的影响。结果表明：偏磷酸铝的含量、Ａｌ／Ｐ原子比及处理温度对预制件的抗压性能均有显著影响，加入５％偏磷酸铝粘接剂溶液的预制件，经５００°Ｃ处理后的抗压性能满足压渗要求，纤维保持了较好的平直度及分布均匀性，所制备的复合材料抗拉强度大于５００ＭＰａ。

C_f/Si-O-C复杂形状应用构件的制备

结合树脂传递模塑 (RTM)和先驱体浸渍裂解技术 ,以聚硅氧烷 (PSO)为先驱体 ,制备出复杂形状的 Cf/ Si-O- C陶瓷基复合材料应用构件。根据 RTM的工艺要求 ,研究了二乙烯基苯 (DVB) / PSO的交联和裂解 ,DVB/ PSO粘度与温度和时间的关系 ,DVB/ PSO与碳纤维的润湿性以及用作脱模剂的 Ti O2

烧结温度对C_f/SiC复合材料界面的影响

系统地研究了烧结温度对Cf/SiC复合材料界面和力学性能的影响。结果表明 ,烧结温度较低(1 70 0℃ )时 ,由于复合材料的烧结性差 ,纤维与基体间仅仅为一种机械结合 ,因此纤维与基体间结合很弱 ,从而导致复合材料力学性能低。烧结温度提高至 1 80 0℃后 ,由于适量的富碳界面相不仅可避免纤维与基体间的直接结合 ,而且使纤维与基体间的结合强度适中 ,因而复合材料具有很好的力学性能。进一步提高烧结温度至 1 85 0℃或更高温度时 ,由于界面相与纤维间的反应加重 ,纤维本身性能大大降低。同时 ,纤维与基体间结合强度提高 ,因此复合材料的力学性能大大降低。

先驱体转化-热压烧结C_f/SiC复合材料的密化机理

本文采用先驱体裂解—热压烧结方法制备出了Cf SiC复合材料 ,并重点研究了复合材料的致密化过程。结果表明 ,复合材料主要是通过液相烧结而得到致密化的。由于复合材料中聚碳硅烷 (PCS)的裂解不仅有利于烧结液相的形成 ,而且形成了大量的纳米级SiC颗粒 ,因此 ,复合材料能够在较低烧结温度下得到较好的致密化 。

Al_2O_(3f)+C_f/ZL109干摩擦磨损行为及其人工神经网络分析

采用挤压铸造法制备了氧化铝及碳短纤维混杂增强 Ｚ Ｌ１０９ 合金复合材料，考察了该复合材料的干摩擦磨损行为．结果表明：该复合材料的摩擦磨损性能随纤维总体积分数的增加而降低；当纤维总体积分数一定时，随碳纤维含量的增加复合材料摩擦磨损性能降低．采用人工神经网络技术对该复合材料的干摩擦磨损试验结果进行了综合分析，其结果与试验值吻合较好．分析表明：纤维总体积分数较小时，碳纤维含量对复合材料耐磨性的影响较大，随纤维总体积分数的增大其影响减弱；无论纤维总体积分数如何变化，碳纤维含量对复合材料摩擦系数均有较大影响，这是其自润滑作用的结果；载荷较小时，该复合材料摩擦磨损的跑合时间较长；随载荷的增大摩擦系数减小；

先驱体转化─热压烧结法制备C_f/SiC复合材料

以Y2 O3-Al2 O3和MgO -Al2 O3为烧结助剂体系 ,研究了烧结助剂体系及其含量对Cf/SiC复合材料密度与力学性能的影响。结果表明 ,以Y2 O3-Al2 O3为烧结助剂时 ,复合材料的力学性能优于烧结助剂为MgO -Al2 O3时复合材料的力学性能。当烧结助剂为Y2 O3-Al2 O3时 ,随着烧结助剂含量的增加 ,复合材料力学性能不断提高 ,断裂韧性在烧结助剂含量为 12 %时达到最大值 14.83MPa·m1/ 2 。进一步增加烧结助剂的含量 ,复合材料的抗弯强度虽有提高 ,但断裂韧性急剧降低。烧结助剂含量超过 15%后 ,抗弯强度也急剧降低。结果同时证明 ,复合材料的断裂行为取决于纤维 /基体间的界面结合强度 ,即纤维