The growth of graphene on insulating materials is always a focused issue in the field of multifunctional nanomaterials. To investigate the atomistic mechanism of graphene growth on bicrystal diamonds, we initially investigated the process of in situ growth of graphene on bi-crystal diamonds in the presence of a nickel catalyst and further explored the diamond grain boundary (GB) effect on the graphene growth by reactive molecular dynamics (MD) simulations. The detailed dynamic evolution of graphene growth, the counterdiffusion of catalytic nickel atoms/ GB carbon atoms, and the consequent amorphization of GB were observed. The study demonstrated that the presence of GB assists graphene growth, namely, the amorphous C GB atoms participate in the growth of graphene as supplementary carbon atoms, which is in good qualitative agreement with experimental observations. In addition, we demonstrated that the amorphization of GB is caused by the increase of energy at GB driven by the catalysis of nickel atoms. The results further indicate that the diffusion behavior of the amorphous C GB atom in the nickel lattice involves irregular lateral migration instead of pure upward diffusion. In contrast, in the absence of GB, the kinetics of nickel catalyst-induced amorphization of diamond structures is drastically impaired, resulting in lower graphene coverage.
The physical performance of a heterostructure is strongly
influenced
by the adhesion properties. The study of adhesion properties between
graphene and diamond lattice is an inescapable issue in the development
of diamond-based graphene multifunctional nanodevices. Herein, a series
of adhesion intensities have been theoretically examined, and the
optimum facet of diamond and theoretically recommended orientation
angle were obtained, respectively. Moreover, the atomistic peeling
behavior and the effect of three typical graphene topological defects
on adhesion intensity were explored. The study demonstrated that the
presence of double-vacancy defects impairs the adhesion strength due
to the reduction of the contact area. In contrast, the presence of
Stone-Wales defects is conducive to enhancing the adhesion strength.
Interestingly, the effect of single-vacancy defects mainly depends
on the delicate competition between single-atom removal and single-atom
attraction enhancement. Meanwhile, the effects of diamond surface
morphology on graphene adhesion were systematically elaborated by
the modeling of one-dimensional and two-dimensional surfaces, and
randomly rough surfaces. The adhesion details of graphene on regularly
tunable diamonds were explored, and the relations of adhesion intensity
and graphene morphology with the random roughness of a diamond surface
were further revealed in depth. Since the mechanical and electrical
performance of a graphene–diamond heterostructure is sensitively
influenced by the adhesion intensity, our findings provide insight
into the substrate design of graphene–diamond hybrid devices.
Diamond tools are extensively used in ultra-precision machining due to their exceptional performance. However, when machining challenging materials like Ti6Al4V, diamond tools experience significant wear due to poor machining properties and catalytic effects. Tool wear not only impacts machining quality but also escalates machining costs and energy consumption. Cutting fluids are commonly employed to mitigate interfacial reactions and suppress tool wear. However, traditional cutting fluids are difficult to penetrate the cutting area and have limited lubrication and cooling capabilities. Therefore, in this paper, a technique combining graphene nanofluid and minimum-quantity lubrication (MQL) is used to suppress diamond tool wear. Firstly, micro-milling experiments for Ti6Al4V alloy are conducted using diamond tools in the graphene nanofluid MQL and under a dry environment. The experimental results show that tool wear is effectively suppressed by graphene nanofluids. Subsequently, the cutting process in both environments (graphene nanofluid MQL, dry) is simulated. The suppression mechanism of graphene nanofluid MQL for diamond tool wear is evaluated from phase transition, atomic transfer process, and amorphous behavior of diamond structure. The simulation results show that the contact characteristics, cutting force, and cutting temperature are improved by graphene nanofluids. Tool wear is effectively reduced. In addition, the removal efficiency of workpiece materials has also been improved. This work provides a technical basis for exploring the application of graphene nanofluids in diamond tool damage suppression and micro-milling.
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