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石墨烯具有优异的力学性能, 是一种较佳的硬质合金刀具涂层材料. 本文采用分子动力学, 以硬质合金(WC-Co)为基底, 并以Ni为过渡层, 建立沉积石墨烯涂层模型, 模拟Ni, C原子连续沉积和高温退火过程, 研究沉积温度和入射能量对石墨烯涂层生长的影响, 探究石墨烯沉积过程. 模拟结果发现, 当沉积温度为1100 K时, 石墨烯的覆盖率较高, 结构平整. 较高的沉积温度有助于提供足够的动能使碳原子来克服成核的势能障碍, 减少石墨烯生长缺陷. 温度过高导致碳原子不断在优先沉积的碳环处堆积形成多层网状结构和无序结构, 形成的石墨烯涂层覆盖率低. 入射能量的增大有助于减少石墨烯中的空位缺陷; 但入射能量过高, C-C的吸附作用较之C-Ni的吸附作用更强, 导致涂层连续性较差. 入射能量为1 eV时, 涂层表面粗糙度较低, 生长出较多的单层状石墨烯. 1100 K退火时, 碳膜在Ni过渡层同时存在溶解-成核过程, Ni过渡层催化消除了部分石墨烯缺陷, 六元碳环数量增多, 适宜的高温退火有利于缺陷碳环的修复重构和碳链的重排成环, 提高了石墨烯质量. 因此, 当沉积温度1100 K、入射能量1 eV时, 石墨烯沉积完后并退火, 可生长出较高质量的石墨烯涂层.
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. -
Keywords:
- molecular dynamics /
- graphene /
- physical vapour deposition /
- nickel transition layer /
- high temperature annealing
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Atom pair $ {D}_{{\mathrm{e}}} $/eV $ \alpha $/Å–1 $ {r}_{0} $/Å W-Co 0.098 25.14 0.0872 C-Co 0.1114 19.725 0.1743 
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Atom pair $ \varepsilon $/eV $ \sigma $/Å W-Ni 0.07449 2.4180 C-Ni 0.0487 2.9645 W-C 0.0073 3.1411 C-C 0.0050 3.8510 Co-C 0.0017 3.3257 Ni-C 0.0487 2.9645
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