Abstract:Sliding friction experiments were conducted on hot-pressed B₄C ceramic under the condition of sliding contact with themselves in air. The tests were run at average sliding velocity of 1.41 m/s and normal forces ranging from 11. 8 N to 37.6 N. The friction coefficients decrease with the increase of sliding distance and the increase of normal load. The lowest friction coefficient is as low as 0.09, compared to 0.35～0.40 as the initial friction coefficient. X-ray diffraction was used to analyze the sliding surface before and after friction tests. The results show that the tribochemical reaction between B₄C and O₂ produces B₂O₃, and B₂O₃ undergoes a secondary chemical reaction with moisture in the air to form H₃BO₃, which is responsible for the lower friction coefficients. The low-friction mechanism of boric acid is associated with its layered-triclinic-crystal structure. The atoms on each layer are closely packed and strongly bonded to each other, but the layers are widely separated and are held together by van der Waals force. Regarding the wear rate of B₄C ceramics used in friction experiments, there is not any wear could be measured by using a surface profilometer.

Key words: boron carbide; friction coefficient; wear; tribochemistry