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Abstract
Unlubricated tribological behaviors of silicon nitride–boron nitride (Si 3 N 4 -hBN) composites were investigated with two test modes in air by using a pin-on-disc tribometer. Under upper-disc-on-bottom-pin test mode, the addition of hBN to Si 3 N 4 resulted in a significant decrease of the friction coefficient, from 0.54 for Si 3 N 4 against Si 3 N 4 to 0.19 for Si 3 N 4 -20% hBN against Si 3 N 4 . The surface analysis indicated that a tribochemical film consisting of SiO2 and H 3 BO 3 was formed on the wear surfaces. The formation of tribochemical film might be attributed to the embedment of wear debris into the spalling pits on the wear surfaces of Si 3 N 4 -hBN specimen. The wear debris reacted with moisture in air, and the resultant tribochemical film lubricated the wear surfaces. Under upper-pin-on-bottom-disc test mode, the wear mechanism was dominated by abrasive wear, and no tribochemical products could be detected on the wear surfaces. A slight decrease of the friction coefficient, from 0.85 for Si 3 N 4 /Si 3 N 4 to 0.56 for Si 3 N 4 /Si 3 N 4 -30% hBN, was obtained, which might be attributed to the layered structure of hBN.
ACKNOWLEDGEMENTS
The authors thank the Natural Science Foundation of China (No. 50672074) and Laboratory for Mechanical Behavior of Materials.
Review led by David Burris