Pressureless sintering of SiC matrix composites reinforced with nano-β-SiC and graphene

Silicon carbide (SiC) is an effective material for high-temperature engineering applications owing to its desirable properties such as high elastic modulus, high hardness, and melting temperature, high thermal conductivity, good corrosion and oxidation resistance, low density, and coefficient of thermal expansion compared with other advanced ceramics. Nevertheless, poor sinterability and low toughness limit its use, which can be overcome using appropriate additives. In this study, the effect of different amounts of nano-β-SiC (0, 5, 10, and 15 wt.%) and graphene (0, 1, 2, and 3 wt.%) particles on the sinterability behavior and microstructure of SiC composite has been investigated. After weighing, dispersing nano-β-SiC and graphene, and mixing the starting materials, milling was carried out at 180 rpm for 3 h. The materials obtained were then compressed uniaxially under a pressure of 75 MPa and then were compressed again through CIP under 150 MPa. To remove volatile products, the pyrolysis process was performed at 800 °C under Ar atmosphere. Finally, the samples were sintered at 2200 °C for 2 h by the pressureless sintering process. XRD analysis was used to investigate the phases and FESEM images were used to study the microstructure. According to the XRD patterns, β-SiC particles were converted to α-SiC, which was accompanied by the elongation of SiC grains. Also, no reaction was observed between graphene and the SiC matrix. According to the FESEM images, the samples containing 5 wt.% nano-β-SiC and 1 wt.% graphene showed a uniform distribution of reinforcement particles but with increasing the amount of the reinforcement particles, agglomeration was observed. According to the results, upon increasing the nano-β-SiC up to 5 wt% and graphene up to 1 wt.%, all the measured properties including relative density, and linear shrinkage improved and reached 99.04%, and 18.01%, respectively. However, with increasing the additives, these properties deteriorated due to increasing porosity and agglomeration in the composite structure.