Morphological optimization of process parameters of randomly oriented carbon/carbon composite

Abstract

A microstructure analysis is carried out to optimize the process parameters of a randomly oriented discrete length hybrid carbon fiber reinforced carbon matrix composite. The composite is fabricated by moulding of a slurry into a preform, followed by hot-pressing and carbonization. Heating rates of 0.1, 0.2, 0.3, 0.5, 1, and 3.3°C/min and pressures of 5, 10, 15, and 20 MPa are applied during hot-pressing. Matrix precursor to reinforcement weight ratios of 70:30, 50:50, and 30:70 are also considered. A microstructure analysis of the carbon/ carbon compacts is performed for each variant. Higher heating rates give bloated compacts whereas low heating rates give bloating-free, fine microstructure compacts. The compacts fabricated at higher pressure have displayed side oozing of molten pitch and discrete length carbon fibers. The microstructure of the compacts fabricated at low pressure shows a lack of densification. The compacts with low matrix precursor to reinforcement weight ratios have insufficient bonding agent to bind the reinforcement whereas the higher matrix precursor to reinforcement weight ratio results in a plaster-like structure. Based on the microstructure analysis, a heating rate of 0.2°C/min, pressure of 15 MPa, and a matrix precursor to reinforcement ratio of 50:50 are found to be optimum w.r.t attaining bloating-free densification and processing time.

Influence of hot-pressing pressure on the densification of short-carbon-fiber-reinforced, randomly oriented carbon/carbon composite

“…4, it can be seen that the density of Compacts DE-1 and DE-4 is not mentioned because these failed, either during hot pressing, or during carbonization. The causes of their failure were presented in our previous work [11]. The density of Compacts DE-2 and DE-3, as depicted in Fig.…”

“…Some of these extended applications include nuclear reactor components [6], brake discs for high speed vehicles [7], components for chemical plant equipment [8], artificial body parts [9], and bipolar plates for polymer electrolyte membrane (PEM) fuel cells [10][11][12][13]. Of significance is that these areas do not require the very high levels of mechanical properties needed for space and military applications.…”

“…2. A detailed discussion about these micrographs was presented in our earlier work [11]; however, for a one-to-one comparison, they are briefly described here. The FESEM images of the same compacts after three densification cycles, each comprising resin impregnation, thermosetting, and carbonization, are depicted in Fig.…”

“…Hence, there is still scope to tailor the hot-pressing method using various combinations of short carbon fibers, partial hot-pressing-assisted carbonization under low heat, and complete carbonization under higher heat. In earlier work [11], we worked on morphological optimization of the hot-pressing parameters of a 'randomly oriented, hybrid carbon-fiber-reinforced, mesophase-pitch-derived, carbon-matrix C/C' composite. Though the density and mechanical properties achieved in our work with the C/C composite were very good, further enhancement of the properties of this particular C/C composite could widen its scope of application.…”

“…Though the density and mechanical properties achieved in our work with the C/C composite were very good, further enhancement of the properties of this particular C/C composite could widen its scope of application. Hence, in the present work, low-pressure densification of some of the coupons from the previous study [11] was done using liquid phenolic resin. The influence of hot-pressing pressure and reinforcement wt% on the densification, microstructure, and mechanical properties of the resulting composite were investigated.…”