Background: Graphitization behavior of diamond has received an increasing interest in nanoscale machining of some hard and brittle materials. Diamond has always been an important and excellent tool material in cutting area. However, the graphitization of the diamond tool is inevitable when it was used in special conditions. It is indicated that the graphitization of diamond crystal has great influence on the wear resistance of diamond cutting tool. The graphitization behavior needs to be investigated extensively in nanoscale with an atomic view. Molecular dynamics simulation provides a useful tool for understanding of the graphitization mechanism of diamond. The investigation on graphitization behavior of single crystal diamond can also provide a useful reference for the application of diamond cutting tool.

Materials and Methods: In this paper, a molecular dynamics (MD) diamond crystal model is built to examine the graphitization behavior of diamond under various conditions. The sixfold ring method was employed to identify the structural characteristics of graphite and diamond. The effects of temperature and crystal orientation on the graphitization of diamond have been revealed. Considering the effect of temperature, the anisotropy of diamond graphitization against various crystal planes is presented and discussed carefully. The nano-metric cutting model of diamond tool evaluated by the sixfold ring method also proves the graphitization mechanisms in atomic view.

Results: Results indicate that the sixfold ring method is a reliable method to evaluate the graphitization behavior of diamond crystal. There exists a critical temperature of the graphitization of diamond. The results also show that {111} plane is more easy to get graphitization as compared with other crystal planes. However, {100} plane of diamond model presents the highest antigraphitization property.

Conclusion: The obtained results have provided the in-depth understanding on the wear of diamond tool in nano-metric machining and underpin the development of diamond cutting tool.

背景：金刚石的石墨化行为在一些硬脆材料的纳米级加工中受到越来越多的关注。金刚石一直是切削领域重要而优良的刀具材料。但是，金刚石工具在特殊条件下使用时，石墨化是不可避免的。表明金刚石晶体的石墨化对金刚石刀具的耐磨性有很大影响。石墨化行为需要用原子视图在纳米尺度上进行广泛研究。分子动力学模拟为理解金刚石的石墨化机制提供了有用的工具。对单晶金刚石石墨化行为的研究也可为金刚石刀具的应用提供有益的参考。

材料与方法：在本文中，建立了分子动力学（MD）金刚石晶体模型来检查金刚石在各种条件下的石墨化行为。采用六环法鉴定石墨和金刚石的结构特征。揭示了温度和晶体取向对金刚石石墨化的影响。考虑到温度的影响，对金刚石石墨化对各种晶面的各向异性进行了详细的介绍和讨论。用六环法评价的金刚石刀具纳米级切削模型也证明了原子观上的石墨化机制。

结果：结果表明，六环法是评价金刚石晶体石墨化行为的可靠方法。金刚石的石墨化存在临界温度。结果还表明，与其他晶面相比，{111}晶面更容易石墨化。然而，金刚石模型的{100}面呈现出最高的抗石墨化性能。

结论：所得结果为深入了解金刚石刀具在纳米加工中的磨损提供了依据，为金刚石刀具的发展奠定了基础。