Material characterization of polycrystalline diamond compacts (PDC)

The mechanical and the thermal behavior of polycrystalline diamond compact (PDC) cutters were evaluated in this study. A systematic method for classifying failure of PDC cutters was developed. Four mechanisms of PDC cutter failure--smooth wear, microchipping, gross fracturing, and delamination, were identified. Testing procedures were developed to examine these failure mechanisms. Edge-loading tests showed that gross failure is produced by the cutter normal force and that the rock must contain hard minerals for this type of failure to occur. The resistance of PDC cutters to gross fracturing is found to increase with increasing the negative rake angle of the cutter. However, cutting tests showed that increasing the negative rake angle increased the susceptibility of cutters to microchipping damage.; The double-torsion test was employed to measure the fracture toughness and study the processes of crack propagation of polycrystalline diamond. The value of fracture toughness of about 13 MPa{dollar}sqrt{lcub}rm m{rcub}{dollar} is surprisingly high. Subcritical crack growth is shown to be negligible and crack deflection is shown to be an important toughening mechanism. A cyclic compressive loading test was employed to investigate the fatigue behavior of PDC cutters. Fatigue damage was observed both in the diamond layer and in the carbide backing. Fatigue crack propagation in the cemented carbide is intergranular and is due mainly to the tensile stresses that arise upon unloading. On the other hand, the failure of polycrystalline diamond started with the formation of spalled flakes produced by extensional splitting cracks in the direction subparallel with the uniaxial compressive stress. As the crack deepened, the size of the fractured zone decreased. Failure at the root of the crack was then more probably in multiaxial compression, in which the diamond grains were crushed and disintegrated.; Thermal degradation of PDC cutters was assessed using electrical resistance measurement and SEM investigation. The sintered diamond was found to lose integrity when the cutter temperature exceeds 700{dollar}spcirc{dollar}C. Model calculations, verified by independent experimental observations, showed that very high residual stresses are induced in PDC cutters during the sintering process. The inclusion of the residual stresses has important consequences in developing a correct understanding of the loading and failure of a PDC cutter.