Abstract
A possible mechanism for the occurrence of numerous shallow cracks, which were observed on the rubbing surface of cemented carbide, was studied The experiments were conducted using an apparatus simulated mechanical face seal composed of two kinds of ceramics rings and cemented carbide ring, with distilled water as the liquid to be sealed. The variations of rubbing surfaces of cemented carbide were examined in detail by using the Vickers indentations. Although the crack spacing gradually decreased with increasing the number of cracks, new crack was hardly formed between the precracks if the crack spacing fell below a critical value. If the Vickers indentation tests were conducted on the rubbing surface where the crack spacing was larger than the critical value, indentation cracks with almost the same length as the neighboring precracks could be formed. It was also found that the surface near the crack piled up in both cases where the crack was caused by rubbing test and by the Vickers indentation test. These results suggested that the cracking occurred by the tensile residual surface stress. A method to predict the magnitude of the tensile residual stress by measuring the surface profile was also proposed.
