Wear mechanisms of silicon carbide subjected to ultrasonic nanocrystalline surface modification technique

A modified surface layer with a thickness of about 4 µm was produced at the top surface of sintered silicon carbide (SiC) by ultrasonic nanocrystalline surface modification (UNSM) technique. The objective of this study is to investigate the effectiveness of modified surface layer on the tribological properties and to give insight into the wear mechanisms of SiC. The tribological properties of the untreated and UNSM-treated SiC disk specimens against silicon nitride (Si3N4) ceramic ball were investigated using a ball-on-disk tribometer at normal loads of 1 N, 5 N and 10 N under water-lubricated conditions. Results revealed that the friction coefficient was found to be 0.08 and 0.065 for the untreated and UNSM-treated specimens at a normal load of 1 N which may be attributed to the modified surface layer at the top surface having higher hardness and smoother roughness with a small number of porosity, respectively. This reduction in friction coefficient enables to reduce energy consumption of water-based tribological systems. Wear track analysis was conducted using a nanoscale hybrid microscopy (NHM). NHM images showed that severe polishing and grooving marks were observed on the untreated specimen, while only mild grooving marks were observed on the UNSM-treated specimen. It was also confirmed that the UNSM technique changes the wear mechanisms of SiC: oxidative-adhesive-abrasive-micro fracture wear takes place in the untreated specimen, while adhesive-abrasive wear takes place in the UNSM-treated specimen. Application of UNSM technique would be highly advantageous for water-lubricated ceramic bearings.