氮化硅陶瓷球精加工表面缺陷的研究

Surface Defects Analysis of Si_3N_4 Bearing Balls in Lapping Process

将3种不同直径的氮化硅球坯采用循环加工方法研磨成G5级轴承用陶瓷球。研究了研磨过程中陶瓷球的磨损行为并将磨损缺陷按光学显微镜下的形貌分成5类。采用扫描电子显微镜观察分析各种缺陷并用陶瓷材料断裂力学解释凹坑与裂纹缺陷的形成。研究结果表明,异常的磨粒作为尖锐压头产生凹坑。各种裂纹主要是由起钝压头作用的上研磨盘产生的。材料的晶体结构变化产生雪花缺陷,雪花缺陷抵抗磨粒磨损的能力较差。精研过程中不正确的加工压力和没有破碎的硬磨粒产生擦伤和划痕缺陷。提高球坯圆度,降低粗研加工的载荷和速度可以减少裂纹缺陷。提高磨粒质量可以减少精研中各种机械加工缺陷。

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.