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采用第一性原理方法，对孕镶金刚石基底表层Co原子不同嵌入深度时金刚石涂层膜基界面结合作用进行仿真计算分析，以探究基底中黏结相Co的嵌入深度对金刚石涂层膜基界面结合强度的影响。计算结果表明：膜基界面结合能随基底中Co嵌入深度的增加呈先降低后升高的趋势。当Co原子排列位于第三层时，涂层生长易出现明显的石墨结构，Co促金刚石石墨化作用最为显著，膜基界面结合强度达到最小值。分析结构及电荷发现，此时在表面效应及Co-C键键长的共同作用下基底第二层C移至表层，并由sp3杂化转变为sp2杂化，且C的移动导致Co与周围C原子的作用空间增大、作用数量增多，加之Co价层未配对电子较多，易与周围多个碳原子发生电子轨道的混合与重排，最终使得基底表面呈现为石墨结构。Co位于第五层时不再影响基底表面的稳定构型及膜基界面结合强度。Diamond coating has many excellent properties such as extreme hardness, high elastic modulus, high thermal conductivity, low friction coefficient, low thermal expansion coefficient, and good corrosion resistance that are close to natural diamond, making it an ideal new type of wear-resistant tool coating material. However, a large number of experiments have proved that during the deposition of diamond coating, the bonding phase cobalt on the surface of impregnated diamond substrate will generate a layer of graphite at the interface, seriously weakening the adhesive strength between the substrate and the coating. To thoroughly solve this problem, it is necessary to research the theory and microscopic process of graphitization caused by the Co element embedded on the substrate surface. Therefore, this article adopts the first principle theroy to simulate and analyze the interfacial adhesive strength of diamond coating when Co atom is embedded at different depths on the surface of impregnated diamond substrate, in order to explore the influence mechanism of the bonding phase Co element in the substrate on the diamond coating and the
mechanism of Co promoting diamond graphitization. The calculation results show that the interfacial binding energy decreases first and then increases with the increase of Co embedding depth in the substrate. When Co atom is embedded in the third layer, obvious graphite structures are prone to appear at the interface, and Co promotes diamond graphitization most significantly, resulting in the minimum bonding strength between the film and substrate interface. The results of structure and charge indicate that under the influence of surface effect and Co-C bond length, the C atom in the second layer of the substrate move to the first layer and the hybridization mode changes from sp3 to sp2. Meanwhile, this movement leads to an increase in the interaction space and quantity between Co and the surrounding C atoms. In addition, there are many unpaired electrons in the Co valence layer, which can easily mix and rearrange electron orbitals with the surrounding C atoms, ultimately resulting in a graphite structure on the substrate surface. When Co is embedded in the fifth layer, it no longer affects the stable configuration of the substrate surface and the interfacial adhesive strength.
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Keywords:
- diamond coating /
- Co element /
- adhesive strength /
- graphitization
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