Wear and failure mechanisms of polycrystalline diamond compact bits

Abstract

Four mechanisms of polycrystalline diamond compact cutter failure are identified in a detailed study of cutters damaged in both laboratory rock-cutting tests and field operation. One mechanism is smooth wear. This occurs when individual diamond grains are polished away by a combination of high mechanical and thermal loads. A second mechanism is microchipping of the polycrystalline diamond table. This is caused mainly by the action of the bit cutting forces. A third mechanism is gross fracturing. This is caused by the application of excessive normal force to the bit. A fourth mechanism is delamination at the interface between the diamond table and the cemented tungsten carbide substrate. This results both from impact loading in the bit normal-force direction and thermal stress build-up at the interface between the diamond layer and carbide substrate due to the mismatch in the thermal expansion coefficients of these materials. All these processes lead to the formation of a wear flat beneath the cutter. Once this flat forms, repeated frictional heating and cooling cause thermal fatigue which results in the commonly observed heat checking on this surface.