Wear induced ripplocation during dry sliding wear of TiC-based composite

Monolithic TiC and TiC particulate ceramic composite containing 30 and 50 mol.%SiC were consolidated and synthesized using spark plasma sintering (SPS) without sintering aids. The as-sintered bulk samples microstructural evolution and dry sliding room-temperature tribological properties against Al2O3 ball were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman analysis. The role of coefficient of thermal expansion (CTE) mismatch between TiC and SiC as well as cubic to hexagonal SiC phase transformation on the evolution of residual stresses in the composite was also investigated. The friction and wear properties of the monolithic TiC were superior to that of the composite with frictional heating-induced tribo-oxidation playing a dominant role in the wear mechanism. The increase in friction and wear of the composite is attributed to wear-induced stress-relaxation of the previously trapped residual stresses in the composite leading to extensive ripplocation of the TiC grains and consequent SiC grain pull-outs. Herein, we report for the first time on the wear-induced mechanical exfoliation of carbon, its subsequent decomposition into graphite and eventual deformation by micromechanism involving nucleation and propagation of ripples.