Effect Of Micron Diamond On Properties And Texture Of PCD Sintered By Carbon Onions

At present time, the preparation of polycrystalline diamond (PCD) is using diamondmicro-powder as raw material and need to add additives, which are sintered in hightemperature (HT) and high pressure (HP). The additives is not only easy to remain in thePCD but also easy to form carbide, the physical and mechanical properties of additiveresidue and carbide formed are much lower than that of the diamond, which affects the useand processing properties of PCD. Additive-free sintering of PCD is a fundamental way tosolve these problems.Our project team use onion-like carbon (OLC) as raw material to sinter PCD with noadditives for the first time and have succeeded. Research shows that during the sintering atHT and HP, OLC transform into diamond, which are linked to each other to form largediamond particles (up to13nm). But we also found unconverted OLC and graphite in thiskind of PCD. After analysis we realize that the OLC is a kind of symmetrical structure,some pressure will be balanced during sintering, and for the nana-meter scale raw material,the mutual friction between the particles will make the pressure transmission seriouslydamaged, which reduce the conversion rate of OLC and seriously affect the mechanicalproperties of PCD.Annealing nanodiamond at0.1Pa vacuum and1100℃get OLC, mixing with microndiamond and then are sintered at HT and HP. The experiment proves that the OLCprepared in this condition contains diamond core and the transformation of nanodiamondto OLC starting from the surface of diamond nanoparticles and gradually to the center.The best content of micron diamond mixed with OLC are30%、40%、50%and thebest process conditions for sintering are1300℃,6GPa and heating15min. Under thiscondition, while the content of micron diamond is50%, the average Vickers hardness ofPCD is55.9GPa and the density can run up to3.02g/cm~3. During the high temperatureand high pressure sintering, the graphite layer of OLC particles ruptured and linked toruptured particles nearby to transform large diamond particles and particles wereconnected by D-D (Diamond-Diamond) bonds. And the diamond generated by OLC particles can be combined with added micron diamond. So the adding of micron diamondcan reduce the pressure loss during the pressure transmission and increase the conversionrate of OLC, which can greatly improve the performance of PCD.