Thermal Damage Mechanisms And Tribological Properties Of Polycrystalline Diamond Compact

Polycrystalline diamond compact(PDC) is widely used to produce ultra-hard cutting tools and drilling bits for its outstanding mechanical and chemical properties such as high hardness, excellent wear resistance and good corrosion stability. The life of cutting tools and drilling bits will be inevitably affected by the heat from friction and environment during service process. Therefore, it is important to study the thermal damage mechanisms as well as characteristics of friction and wear of PDC. In our work, we firstly had annealed the PDC samples at different temperatures in ambient air and vacuum by using SX-8-10 muffle furnace. Then the microstructures and thermal damage mechanisms of PDC were obtained by analyzing the results of three-dimensional surface topography, XRD, Raman, SEM and EDS. Finally, we had performed the tribological tests of annealed PDCs against Si3N4 balls and further studied the friction characteristics and wear mechanisms at the interface between PDC and Si3N4 ball. The results are as follows:(1) At the temperature of 500℃, numbers of spalling pits appeared on the PDC surface and the stress-induced spalls mechanism was the dominant thermal damage mechanism for annealed PDC surfaces both in ambient air and vacuum. At 800℃, the thermal damage mechanism was a mixed-mechanism including graphitization,oxidation and stress-induced micro-cracks mechanisms. Whereas, the thermal damage mechanism in vacuum was still the stress-induced spalls mechanism. The annealed PDC surface, at 900℃ in ambient air, only contained dendritic phase of Co3O4 because of extensive graphitization and oxidation. In vacuum, many cracks appeared on the PDC surface and some fine diamond grains near the cracks spalled. It demonstrated that the thermal damage mechanism consists of stress-induced cracks and spalls mechanisms.(2) The annealed PDC at 200℃ in ambient air sliding against Si3N4 ball was worn severely because of the shedding of tiny diamonds and abrasive wear. The friction coefficient was controled by diamond-induced transfer film mechanism. The friction coefficient of PDC annealed at 300 ~ 600℃ in ambient air was linearlydependent on the transfer film. With increasing of transfer film, the friction coefficient declined and wearing capacity increased. The friction coefficient of PDC annealed above 600 was controlled by surface roughness, surface graphitization and diamond-induced transfer film. PDC had worn slightly and the wearing capacity was dependent on surface roughness and spalled tiny diamonds.(3) The annealed PDC at 200℃ in vacuum sliding against Si3N4 ball, with the lowest friction coefficient, was worn severely because of the shedding of tiny diamonds and abrasive wear. The friction coefficient was linearly dependent on the transfer film because of its friction-reducing performance. During the tribological test,PDC annealed at 300 ~ 600℃ in vacuum sliding against Si3N4 ball, the friction coefficient declined and wearing capacity of PDC and Si3N4 ball increased.