The Influence of Site of Co and Holes in PCD Substrate on Adhesive Strength of Diamond Coating with PCD Substrate

Abstract

Polycrystalline diamond (PCD) prepared by the high temperature and pressure method often uses Co as a binder, which had a detrimental effect on the cutting performance of PCD, thus Co needed to be removed. However, the removal of Co would cause residual holes and also make the cutting performance of PCD poorer. To address this issue, hot filament chemical vapor deposition (HFCVD) was used. During deposition, the residual holes cannot be filled fully, and Co would diffuse to the interface between CVD diamond coatings and the PCD substrate, which influenced the adhesive strength of the diamond coating with the PCD substrate. In order to investigate the influencing mechanism, both experiments and the density functional theory (DFT) calculations have been employed. The experimental results demonstrate that Co and the holes in the interface would reduce the interfacial binding strength. Further, we built interfacial structures consisting of diamond (100), (110), (111) surfaces and PCD to calculate the corresponding interfacial binding energy, charge density and charge density difference. After contrast, for Co and the holes located on the (110) surface, the corresponding interfacial binding energy was bigger than the others. This means that the corresponding C-C covalent bond was stronger, and the interfacial binding strength was higher. Based on this, conducting cobalt removal pretreatment, optimizing the PCD synthetic process and designing the site of Co can improve the performance of the PCD substrate CVD diamond coating tools.