INTERFACE STRUCTURE,PROPERTIES AND BONDING MECHANISM OF 25 mm-DIAMETER POLYCRYSTALLINE DIAMOND COMPOSITES

25 mm-diameter polycrystalline diamond composites of typical interface structures were sintered in situ under 5.8 GPa at 1500℃ for ３ min by use of different thick cobalt foils as medial layer and different diamond grain sizes. The linear distribution of Co K _{α (EDW) and characteristic X-ray image of cobalt near the interface was examined by SEM. The bonding strength of the PDC interface was measured by shear test and the heat resistance was measured by the numbers of quench and compression tests. The bonding mechanism of the interface between cemented tungsten carbide and polycrystalline diamond was discussed. The results show that the bonding strength of the PDC interface increased firstly from 2.67 GPa to 2.82 GPa then decreased to 1.47 GPa and the heat resistance decreased from 15, 11 to 5 times separately as the interface cobalt changed from even distribution to high content of cobalt then to cobalt medial layer, compared to the small grain size(10 μm) interface(2.67 GPa, 15 times) the bonding strength and the heat resistance of the coarse grain size(80 μm) interface(0.52 GPa, 7 times) decreased greatly. These indicated that the properties of the PDC interface were depended not only on the content and existential state of the cobalt but also on the grain size of diamond at the interface.}