SEM observations of the sliding behavior of A12O3 and CBN against steel

Abstract

AbstractBoth aluminum oxide (A12O3) and cubic boron nitride (CBN) are being used as the abrasive medium in grinding wheels. To compare the effectiveness of these abrasives, a study was made, using the scanning electron microscope (SEM), to observe the sliding behavior and surface damage resulting from single particles of polycrystalline A12O3 and CBN sliding dry against hardened M‐50 tool steel. These experiments were run in the chamber of the SEM, which permitted direct observation of the contact areas at high magnifications. Friction force was monitored and videotape recordings were made continuously during these tests. Significantly lower friction and smoother wear tracks were obtained with the CBN. The A12O3 grit produced much sharper ridges and considerable microcracking on the ridges. These microcracks were formed perpendicular to the wear track. The wear tracks obtained in the SEM were compared with the surfaces produced by surface grinding hardened steel with both CBN and A12O3 wheels. At high magnifications, marked similarities between the ground surfaces and the surfaces produced by the basic sliding tests were noted. It is suggested that because of the large number of microcracks formed during the grinding process with the A12O3, the fatigue life of parts ground with an A12O3 wheel would be shorter than those ground with CBN. Practical experience indicates that this is true.