WC-Co cemented carbide has excellent cutting performance, which is a potential tool material. But when it is used as cutting ultra-high strength and high hardness materials, the machining accuracy and service life of the tool are significantly reduced. Graphene is a potential coating material for cemented carbide cutting tools due to its excellent mechanical properties. In this work, molecular dynamics (MD) is used to simulate the deposition of nickel transition layer and high-temperature catalytic growth of graphene in cemented carbide. The Ni and C atomic deposition process and the high temperature annealing process are simulated, and a combination of potential functions is adopted to continuously simulate these two deposition processes. The effect of deposition temperature and the effect of incident energy on the growth of graphene are analyzed. The healing mechanism of nickel-based catalytic defective graphene under high-temperature annealing is explored in detail.
The simulation results show that at the deposition temperature of 1100 K, the coverage of graphene is higher and the microstructure is flat. The higher temperature helps to provide enough kinetic energy for carbon atoms to overcome the potential energy barrier of nucleation, thereby promoting the migration and rearrangement of carbon atoms and reducing graphene growth defects. Too high a temperature will lead to continuous accumulation of carbon atoms on the deposited carbon rings, forming a multilayered reticulation and disordered structure, which will cause a low coverage rate of graphene. The increase of incident energy helps to reduce the vacancy defects in the film, but excessive energy leads to poor continuity of the film, agglomeration, the more obvious stacking effect of carbon atoms and the tendency of epitaxial growth. When the incident energy is 1 eV, the surface roughness of the film is lower, and more monolayer graphene can be grown. During annealing at 1100 K, the carbon film dissolves and nucleates simultaneously in the Ni transition layer, and the nickel transition layer catalyzes the repair of defective graphene. The graphene film becomes more uniform, and the number of hexagonal carbon rings increases. Appropriate high-temperature annealing can help to repair and reconstruct defective carbon rings and rearrange carbon chains into rings. Therefore, when the deposition temperature is 1100 K and the incident energy is 1 eV, graphene can be deposited and annealed to grow a high-quality graphene coatings. The simulation results provide the reference for preparing the cemented carbide graphene coated tools.
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