Exploring structural evolution and graphitization of the interface between tungsten and diamond (1 1 1) surface: A DFT study

In the ultra-precision machining field, tungsten (W) is a promising material as a polishing disc for machining diamond, which is easier to obtain high-quality diamond surfaces than cast iron. The removal mechanism of the diamond during high-speed polishing is considered surface graphitization. In this work, the diamond graphitization mechanism induced by tungsten is revealed by the density functional theory (DFT). The results show that the W adatoms at the fcc sites can activate the interlayer C-C bonds, causing the surface carbon atoms to separate. Notably, the electron transfer of W atoms and the structure contraction of the diamond surface cause the graphitization. Moreover, the movement of W adatoms intensifies the diamond surface structure transformation and graphitization process. It is worth noting that the W adatoms of the fcc and hcp sites have different contributions to the surface carbon atom separation during the interfacial sliding process. When the W atoms cross the hcp sites, the pulling force of the W-C bonds promotes the reconfiguration of the separated surface carbon atoms. The diamond-to-graphite transition is attributed to catalyst activation by W adatoms, diamond surface structure contraction, and mechanical tensile stress by the W-C bonds.