Surface defects analysis of Si₃N₄ bearing balls in lapping process

Three kinds of silicon nitride ball blanks with different diameters were lapped and polished to G5 degree bearing balls. Wear behaviors of these balls in lapping process were experimentally studied and wear defects were classified into five columns according to their morphologies under optical microscope (OM). All defects were examined using SEM and the formation of flaws and cracks were interpreted with fracture mechanics of ceramics. The results indicate that these defects are dominated by different wear mechanisms. Irregular lapping abrasives act as sharp indenters produce flaws. Various cracks are mainly produced by upper lapping plate as blunt indenters. The reason for snow defects is differences in crystal structures and snow defects show poor resistance to abrasive wear. Abrasion and scratch defects are caused by false lapping load and unbroken hard abrasive particles in final process. Better blank ball roundness and lower lapping load and speed at early lapping stages may reduce various cracks. Increase the quality of abrasive particles can reduce all machining defects at final lapping steps.