Development of vapor grown carbon fibers (VGCF) reinforced carbon/carbon composites

C/C composites are developed using vapor grown carbon fibers (VGCF) with two types of pitches as matrix precursor. The composites are carbonized at 1000 degrees C by applying the isostatic pressure throughout the carbonization process and further heat treated at different temperatures up to 2500 degrees C in the inert atmosphere. By applying iso-static pressure one can able to developed VGCF based C/C composites possessing the very high bulk density (1.80 g/cm(3)) and apparent density (2.01 g/cm(3)) only by heat treatment up to 2500 degrees C without any densification cycle. This high value of density is due to the extremely strong fiber-matrix interactions and self sintering between the VGCF fibers during carbonization process under iso-static pressure. From the SEM study it reveals that, fiber-matrix interactions are strong and fiber boundaries merges with each other, also there is not a evidence of matrix shrinkage cracks in case 1500 degrees C heat treated composites. On the other hand, in 2500 degrees C heat treated composites, there is evidence of uniform fiber-matrix interfacial cracks and porosity in nanometer dimensions. This is due to the change in fiber morphology above HTT 1500 degrees C. But the formation of nano width cracks does not affect on the mechanical properties of composites. The compressive strength increases from 95MPa of 1500 degrees C to 105 MPa of 2500 degrees C heat treated composites. However, hardness decreases due to the increase in the degree of graphitization of composites on 2500 degrees C. The study reveals that by controlling processing condition and the uniform dispersion of VGCF fibers in the matrix phase, it can be possible to developed nano porosity at fiber-matrix interface