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 A degrees 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-m(0.5)) 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 (mu) over monolithic SiC (mu = 0.53-0.58) due to the self-lubrication ability of CNT.