Sub-surface microstructural investigation for establishing micro-mechanisms of wear in sliding of SiC and SiC-WC ceramics

Dual-beam FIB/FEG-SEM and TEM/HRTEM observations of sub-surfaces of SiC and SiC-50 wt% WC composite disks worn against SiC ball have provided important insights into the micro-mechanisms of material removal and the role of WC towards suppressing the same. Sub-surface analysis reveals the silicon oxide rich tribochemical layer just underneath the worn surfaces of monolithic SiC. Further below this tribochemical layer, dislocations and twins in SiC grains, as well as micro-cracks, are identified. Micro-cracks get extended up to similar to 2 mu m depth below the layer, eventually leading to material removal in SiC ceramics. In case of the SiC-WC composite, neither is the tribochemical layer dominant, nor is twin/dislocation networks seen to extend beyond the SiC/WC interfaces. Overall, the present study highlights that WC particulate reinforcements in SiC-WC composite minimize the wear damage by suppressing oxidative wear and restricting the generation of micro-cracks, which otherwise form extensively due to stress build-up at the tips of dislocations or twins in SiC grains.