Spark plasma sintered multiwalled carbon nanotube/silicon carbide composites: densification, microstructure, and tribo-mechanical characterization

Multiwalled carbon nanotube (MWCNT)/silicon carbide (SiC) composites were fabricated by spark plasma sintering at 2000 °C under 50 MPa for 10 min in Argon. Physical properties and Williamson–Hall analyses of X-ray diffraction patterns indicated strong influence of CNT on densification, crystallite size, and lattice micro-strain of pure SiC. Structural retention of CNTs, CNT/SiC interactions, and formation of 3–4 nm thick interface in sintered composites were confirmed through electron microscopy. Meyer’s exponent (1.84–1.89) of hardness data indicated almost similar indentation size effect in the studied specimens. Modified proportional specimen resistance model revealed formation of compressive surface residual stress and enhanced elastic response in CNT/SiC composites compared to pure SiC. R-curve sensitivity of present composites (toughening exponent, n ranged from 0.231 to 0.247) was found to be much improved than that obtained for pure SiC (n = 0.155). The 0.3 wt% MWCNT/SiC composite offered the highest toughness (3.93–5.56 MPa-m0.5) within the investigated loading range which was 17–31 % higher than those of monolithic SiC. Present composites also offered much better wear resistance up to 20 N. Wear rate of 0.1 wt% CNT/SiC composite was found to be more than 47 % lower than that obtained for pure SiC. At the highest CNT loading i.e., 1.2 wt%, composite also showed 10–12 % reduction in friction coefficient (μ) over monolithic SiC (μ = 0.53–0.58) due to the self-lubrication ability of CNT.