Fibra De Carbono

International Journal of Mechanical and Materials Engineering (IJMME), Vol.6 (2011), No.1, 133-139

CARBON-CARBON COMPOSITES BY PREFORMED YARN METHOD P. Naika, N.V. Londeb, A.O. Surendranathana and T. Jayarajub
Department of and Metallurgical and Materials Engineering National Institute of Technology, Surathkal, India-575025 b Department of Mechanical Engineering National institute ofEngineering, Mysore, India-570008 Email: padmayyanaikshaniyara@yahoo.com ; nvlondhe@yahoo.com Received 16 June 2010, Accepted 3 December 2010 ABSTRACT The conventional techniques of manufacturing carboncarbon(C/C) composites have reportedly encountered problems because the resulting C/C composites exhibit non-uniform properties such as bending strength and density. A novel method of manufacturing C/Ccomposites by preformed yarns (PY) is used. The matrix powder consists of coke powders and the binder. The preformed yarn contains the matrix powders inside the carbon fiber bundle and coated on circumference with nylon-6 polymer. This preformed yarn is then chopped and hot pressed at about 600°C to get bars and pellets. These are again heat treated at 1500°C and further impregnated by one more pitchcycle, again heat treated at 2200°C. The tests for hardness, compression strength, Creep strength, resistance to oxidation, and fracture toughness are conducted on these pellets and bars. The micostructural analysis in SEM is done. These tests reveal that the properties obtained from PY method are superior to the properties obtained from any other conventional method. Key words: Tow, Precursor,Preformed yarn, Carbon fiber, Carbon-Carbon composites. 1. INTRODUCTION One of the most important reinforcement fibers in all kinds of composites is carbon fiber. Carbon /Carbon (C/C) is a lightweight, high-strength composite material capable of withstanding temperatures over 3000°C in many environments. Composite structures can be tailored to meet varied physical and thermal requirements throughweaving architecture design (Fatz et al., 1992). C/C offers a high performance, cost effective alternative to refractory metals. Aerospace components commonly fabricated from C/C includes rocket motor nozzle throats and exit cones. Aerospace structural C/C composites are often manufactured using woven 2D or 3D C-fiber fabrics, and are sometimes densified using hot isostatic pressing (Pudhi, 1992).Conventional production methods of manufacturing C/C composites include CVD in which a thermosetting resin binder is carbonized. A preform of carbon fibers having a specified shape is heated in a furnace to a high temperature, while a hydrocarbon gas is fed to the furnace. The gas is thermally cracked to form carbon, which then deposits uniformly on the fiber surfaces. The resulting preforms arethen 133 charred to carbon, and densified by adding carbon by chemical vapor deposition (CVD). In other processes, the yarns or woven/nonwoven fabrics of carbon fibers are shaped into various structural shapes, with the use of a thermosetting binder such as phenolic or epoxy resin (Corum et al., 2001).The structure is subsequently heated in an inert gas atmosphere to carbonize the resin. Theseconventional techniques have reportedly encountered problems because the resulting C/C composites lack uniformity in properties such as bending strength and density (Davis and Meier, 2004). The processes are also complicated and time consuming. Across Co. Ltd has developed a unique manufacturing process of C/C composite, utilizing preformed yarn which is superior to conventional method of CVD orimpregnation method ( Alman et al., 1998).This unique method has enabled drastically reduced processing time. This improvement allows various kinds of customers needs for reasonable time periods. The new method has also resulted in dramatic cost reductions for the manufacturing of C/C composites (Economy et al., 1992). PAN fibers are white with a density of 1.17 g/cm3 and molecular structure comprised...