Research On Fabrication And Properties Of Graphite Fibre Reinforced Copper Matrix Composite

Graphite fiber are used as the reinforced material in the copper matrix. The graphite fiber reinforced copper matrix composites not only has excellent mechanical strength and electrical and thermal conductivity, but also has good abrasion resistance. The composites have very broad applications. Therefore, it may become an alternative material for electric locomotive pantograph slide.In this paper, the optimal method of the coating surface of graphite fiber was found through comparing electroless copper plating and electroplating. The wetting problem between graphite fiber and copper matrix was solved through the metallization on the surface of graphite fiber. And the pretreatment process of graphite fiber, such as gluing and coarsening was studied. The graphite fiber reinforced copper matrix composites were prepared by cold press molding. The effect of solvent wet mixing process and molding pressure on the density of the composites was studied. The composite material was sintered through the vacuum sintering. The optimal sintering temperature, holding time and some other factors affecting on the physical properties of the composites were studied. The friction and wear mechanism of the composite was studied by the current carrying friction and wear testing machine. The friction and wear mechanism of the composite was also investigated.The results showed that: the good quality and uniform thickness of copper coating on the surface of the graphite fiber was obtained through the optimization parameters of the orthogonal experiments. The optimum parameter was: 15 g CuSO4, 5H2 O, 30 g EDTA-2Na, 10 ml formaldehyde and the temperature of the water bath was 60 oC; the optimum pH of copper plating reaction was 12.4; the stability and uniformity coating by using the air stirring method was obtained. The acidic plating solution for copperplating was used, formulation of the main component was: 100 g/L CuSO4?5H2O, 180 g/L H2SO4; the suitable ratio of copper ions and sulfate ions could be helped to improve the dispersion ability of the bath and avoid the "black heart" on the process of electroplating; adding additives could make the layer of copper-plating be more smooth and bright. The optimized process was as follows: 1~2 V, 5~15 min, 30 oC of he bath temperature. Ultrasonic assisted in the electroplating process could improve the copper plating. Two kinds of copper plating technology has theirs own advantages and disadvantages, that is electroplating copper technology was relatively simple; and copper plating layer was relatively thick; the coating was rough and the resultant force was insufficient. The process of electroless copper plating is slightly complicated, the coating was smooth and the bonding strength between the coating and the graphite fibre was strong.Compared with different mixing methods, the result showed that the solvent wet mixing method combined with the ball milling method gave more uniform and no damage to the fiber surface coating. The optimal pressure of cold press molding was 200 Mpa. The effect of pressure on the density and hardness of the composits was minimal. The best sintering process of the composite was studied: the sintering temperature was 820 oC, the holding time was 2 h. The result showed that graphite fiber content of 12.5 vol% reached the maximum value of 101.2 HV0.2, and the content of 7.5 vol% achieved the best hardness and conductivity combination.The graphite fiber in the matrix of composite had a good self lubrication effect in the process of friction and wear throungh the current carrying friction and wear testing machine. The composite wear rate in the graphite fiber content of 7.5~15 vol% appeared a low value and keep steady; the increasing of the sliding velocity showed little effect to the graphite fiber reinforced copper matrix composite material friction coefficient. The lower load, the more easily "off-line", the more seriously electrical erosion happened; when the load was 40 N the composite wear rate reached a lowest value; In the process of friction and wear of the composite, the arc erosion became serious with the increase of the current carrying strength, the 7.5 vol% graphite fiber reinforced copper matrix composites with high output stability in the process of current carrying friction and wear. The mechanisium of graphite reinforced copper matrix composites in the current friction & wear process was determined to be adhesive wear, abrasive wear & arc erosion.