Development of vapor grown carbon fibers (VGCF) reinforced carbon/carbon composites |
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Authors: | S R Dhakate R B Mathur T L Dhami |
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Affiliation: | (1) Carbon Technology Unit, Engineering Materials Division, National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi, 110012, India |
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Abstract: | 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°C by applying the isostatic pressure throughout the carbonization process and further heat treated
at different temperatures up to 2500°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/cm3) and apparent density (2.01 g/cm3) only by heat treatment up to 2500°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°C heat treated composites. On the other hand, in 2500°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°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°C to 105 MPa of 2500°C heat
treated composites. However, hardness decreases due to the increase in the degree of graphitization of composites on 2500°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. |
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