Papers by Keyword: C/C Composite

Abstract: Using C/C composite and chrome bronze as a friction couple, the frictional wear properties of C/C composite with electric current is studied in this paper. The results have shown that current, velocity and load are important factors to affect the frictional wear properties of C/C composite with electric current. Wear rate of C/C composite increases with the increase of arc energy .The coefficient of friction and the wear rate increase with the increase of velocity when the electric current is constant of 100A. The coefficient of friction increases but the wear rate decreases with the increase of load when the electric current is constant at 100A. The coefficient of friction decreases but the wear rate increases with the increase of current when the load is constant of 80N. Comparing with no electric current, the coefficient of friction of C/C composite with electric current decreases but the wear rate of that increases obviously. The wear mechanism of C/C composite is mainly of electric wear caused by arc erosion under the condition of current-carrying.

Abstract: C/C composites have excellent properties, but it will be rapidly oxidized when temperature is above 500 °C, which limits its applications in high temperature environment. In order to improve Anti-oxidation, using CVD method, a SiC coating is prepared on the surface of C/C composites. We have studied the microstructure of the SiC coating, oxidation resistance and high temperature mechanical properties. The results show that SiC coating has excellent oxidation resistance. When coated sample is oxidized at 1500 °C after 50 hours, its oxidation weight loss rate is only 1.45%, and coated samples can still maintain high mechanical properties at 1200 °C.

Abstract: Reusable spacecraft/supersonic aircraft is research and development towards the realization of a new aerospace transportation system.Because these transport aircraft is to flight at a speed of more than Mach 5,are considering the use of scramjet engine.Because this engine uses air as an oxidant and liquid hydrogen as a fuel,the combustion gas temperature is more than 2500°C.So the combustor is required lightweight material and super-heat-resistant material.In the field of aerospace,SiC-based ceramics that is heat-resistant materials are well known as to maintain the mechanical properties at high temperatures and have a high oxidation resistance.However, this material limit as heat-resistant material is about 1600 °C .Therefore, it can not be used in an environment of scramjet engine combustor.There are the measures by metal structure to be force-cooled by refrigerant fuel,but apply is difficult because the system is complexity and very heavy. In this study use the hafnium-based super heat-resistant ceramics that is having a melting point more than 2000°C. Purpose is to develop a new technique for forming the ceramics mainly composed from Hafnium Carbide (Melting point:3950°C) that is very high melting point and have oxidation resistance by melt impregnation to inside C/C composite.In addition, implement the evaluation of changes in the organization after each process by the cross-sectional observation and strength assessment by three-point bending test.

Abstract: Carbon fiber reinforced carbon matrix composites (C/C) have received much attention due to their excellent high-temperature strength, high thermal conductivity, low coefficient of thermal expansion (CTE), good thermal shock resistance. However, the poor ablation resistance of the C/C restricts its high temperature ablating applications. Making a thin anti-ablation coating on the C/C has been proved to improve the performance effectively. In order to improve the anti-ablation property of the composite, MoSi₂ coatings were deposited by Atmosphere Plasma Spraying (APS) on the SiC covered C/C matrix. The SiC coatings were prepared by pack cementation. Oxyacetylene flame torch was selected to simulate the ablation situation. The ablation temperature was 1800°C. XRD and SEM were employed to discover the diversification of the coatings structure and composition. And the mechanism of anti-ablation of the MoSi2 coatings system was investigated in this paper.

Abstract: A two dimensional model was employed to simulate the densification process of thick-walled hollow cylinder preform of C/C composite. Using the hydrogen inhibition model, carbon deposition processes under different partial pressures were compared and the efficiency of densification was analyzed. Then the density distribution of some definite time was analyzed to explain the mechanism of hydrogen inhibition. The results showed that with the adjunction of hydrogen, density distribution in preform was improved while the deposition process took a longer time.

Abstract: Nowadays, composite material is more and more popular mainly because of its low density and high strength. This paper focuses on experimental research of coarse milling process of carbon fiber reinforced carbon matrix composite (C/C composite) in low spindle speed and large milling depth. The milling force prediction model for milling of composite using the end milling cutter is built by orthogonal experiment. Experiment test shows that the results predicted by the proposed model are in well agreement with measured ones and the milling force increases with the increment of feed per tooth, milling depth and milling width, and the effect of milling speed on milling force is not very obvious. In addition, machining accuracy and quality of machined surface is difficult to satisfactory, because of the existence of the substrate lacunas and carbon fibers in C/C composite, by using the existing ordinary material surface integrity evaluation method.

Abstract: Along with the development of high speed machining technology, the ball end milling cutter’s application is more and more widely. An influence of four control parameters, namely feed, cutting depth, spindle speed and cutting width, on cutting forces is investigated. This paper focuses on experimental research of milling process of carbon fiber reinforced carbon matrix composite (C/C composite). The milling force prediction model for milling of composite using the carbide ball-end tools is built by orthogonal experiment. The experiment results show that : the reliability of the this prediction model is quite high, and the effect of milling speed on milling force is not very obvious, but the milling force increases with the increment of feed per tooth, milling depth and milling width. Using this information, a new prediction model for the milling forces is proposed that can be used for C/C composite milling.

Abstract: Zirconium carbide (ZrC) coatings were prepared on C/C composite via molten salt reaction process at relatively low temperatures of 800-1000°C. During the reaction process, potassium fluorozirconate (K2ZrF6) played a role transporting zirconium from the molten salt to the C/C composite surface. Elevating reaction temperature increased the growth rate of coatings, simultaneously leaded to rougher coatings. The coatings growth rate increased with reaction time at first and then decreased gradually. The ZrC coatings prepared at 900°C for 5h was ~2m thickness. At the early stage, the low solubility of zirconium in the molten salt leaded to the low coatings growth rate. Secondly, the growth rate of the ZrC coatings was controlled by the chemical reaction between C/C composites and zirconium once zirconium was saturated in the molten salts. Thirdly, the control step of coatings formation turned into the diffusion of carbon through the formed ZrC coatings and which leaded to a gradual decrease of growth rate.

Abstract: In this work, on the basis of carbon materials microstructure and morphology, we study on the influence of carbon fiber content , graphite degree and metal impurities on oxidation performance of carbon materials. The result of oxidation test shows that there are more crystal defects at the interface of carbon fiber and carbon matrix, and oxidation activity of carbon atoms near the area of crystal defects is higher than others.Carbon materials with higher fiber content and higher graphite degree, has a better anti-oxidation performance. The presence of impurities, especially metal impurities play a catalysis role in oxidation of carbon materials. After purification, impurities escape from the graphite microcrystal,resulting that the distortion of lattice decreased, that cause the better anti-oxidation performance.

Abstract: C/C composite and TC4 alloy were successfully brazed using 70Ag28Cu2Ti (wt. %) as filler metal at brazing temperature 820 º°C~920 °C for soaking time 5 min ~30 min. The effects of brazing parameters on the microstructures and phase composition and the fracture modes of the brazed joints were investigated by SEM and XRD. The mechanical performances of the brazed joints were measured by a universal mechanical testing machine. The results show that the maximum shear strength of the brazed joint is 28 MPa at brazing temperature 860°C and soaking time 10min. Fracture surface analysis of the brazed joints indicates that the position of the fracture surface is related to the orientation of carbon fiber. The brazed joints are fractured in the C/C composite when the carbon fiber is parallel to the joined surface, and the brazed joints are fractured at the C/C composite / 70Ag28Cu2Ti interface when the carbon fiber is vertical to the joined surface.