Influence of Speed on the Tribochemical Reaction Products and the Associated Transitions for the Dry Sliding of Silicon Nitride against Steel

Dry sliding of Si3N4 against steel has been studied using a pin‐on‐disk machine as a function of speed at a pressure of 15.5 MPa. Four types of friction and wear behaviors can be observed with associated transition in their values, called regions R1, R2, R3, and R4. R1 (0.1 to 1.25 ms‐1) is associated with high friction as well as the wear rate of the pin and the negligible wear rate of the disk. In R2 (1.25 to 3.5 ms‐1) friction is low and the wear rate of the pin is negligible but the wear rate of the disk is high. The friction and the wear rate of the pin as well as that of the disk are high in R3 (3.5 to 6.5 ms‐1). In R4 (6.5 to 12.0 ms‐1) the friction is low. The wear rate of the pin is similar to that in R3, while that of the disk is very low. SEM, EDXA, XRD, and IR reveal that each of these changes is associated with certain tribochemical interaction. R1 is associated with reaction between Si3N4 and water vapor to form hydrated silica (SiO2·nH2O), R2 is controlled by softening of SiO2·nH2O, R3 is characterized by microfracture and limited formation of Y2SiO5, and R4 is associated with increased formation of Y2SiO5 and SiO2.