Effect of MWCNTs on Improvement of Fracture Toughness of Spark Plasma Sintered SiC Nano-Composites

Background: Silicon carbide (SiC) ceramics are promising engineering material due to its phenomenal properties, such as strong corrosion resistance, high-temperature hardness, wear resistance, high thermal conductivity and high stability in aggressive environment. The key problem of SiC is low fracture toughness due to its brittle nature and to circumvent this, herein high ductile material like MWCNT was used as reinforcement by different proportions. Methods: Nanocrystalline powdered Silicon Carbide (SiC) of particle size of 40 nm and x % weight ratio of SiC (x = 95%, 90% and 85%) + y % weight ratio of multiwalled carbon nanotubes (MWCNTs) of particle size of 20 nm (y= 5%, 10% and 15%) composites were ball milled and fabricated using spark plasma sintering process with temperature rate of 100 oC/min and external pressure of 50 MPa. The sintered samples were tested according to ASTM standards to verify the mechanical properties of the samples. Further, lattice strain, crystalline size was determined by XRD and crack bridging mechanism was studied by FESEM. Results: It was observed that the uniform distributions of MWCNTs were achieved through ultrasonication and ball milling processes, which play a predominant role in increasing fracture toughness. The fracture toughness of the composite improves drastically from 3.71 MPa m 1/2 (100% SiC) to 10.21 MPa m 1/2 (85% SiC-15% MWCNT). The theoretical and relative densities of the materials were gradually reduced due to the increase in MWCNTs which is due to the lower density of the reinforcement material and an increase in porosity of the samples. Conclusion: The MWCNTs act as a bridging aid in sintered samples, FESEM image signifies some pull-outs and crack branching mechanism of MWCNTs which is the reason for increase in the fracture toughness of SiC.