Wear diagram for sliding of silicon nitrides

Knowledge of the friction and wear behavior of ceramics is essential for their successful tribological applications in advanced mechanical systems. Understanding of this important behavior is very limited because of the complexity of the wear processes. In this study, wear diagrams, which are three-dimensional representations of the dependence of the wear on the applied pressure and the sliding velocity, were constructed from sliding test data with silicon nitride specimens. Two kinds of silicon nitride were selected to study the micro-structural effect on the wear behavior. A multi-wear tester with pin-on-disk test geometry was used. The applied pressure and the sliding velocity ranged from 1 to 100 MPa and 0.01 to 0.30 m/s, respectively. The results show the existence of two distinct regions for the mild and the severe wear in wear diagrams of both materials, but with different proportions of the two regions. Scanning electron microscopy (SEM) of the worn area shows clearly that different wear mechanisms dominate in the mild and severe wear regions. A possible wear transition model from mild to severe wear is discussed based on SEM observations of surface damage and the wear diagrams.