Graphitization as a precursor to wear of diamond in machining pure iron: A molecular dynamics investigation
Graphitization as a precursor to wear of diamond in machining pure iron: A molecular dynamics investigation
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DOI：
10.1016/j.commatsci.2008.10.007
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发表时间：
2009-04-01
影响因子：
3.3
通讯作者：
Komanduri, R.
中科院分区：
文献类型：
--
作者：
Narulkar, R.;Bukkapatnam, S.;Komanduri, R.
众所周知，虽然金刚石是已知的最硬材料，但由于刀具磨损非常快，它不能有效地用于加工纯铁或低碳铁合金。几个研究小组已经假设，观察到的金刚石工具磨损的机制涉及四面体金刚石到六方石墨的初始转化。在通常的机械加工/磨削条件下，碳的化学稳定性更高。在假定的机制中，下一步是石墨碳扩散到铁工件中。尽管有大量的出版物报道了这种现象的实验研究，但这种拟议的机制仍然只不过是一种假设，尽管是一种合理的假设。问题是，进行实验的时间尺度（几秒到一分钟或更长）太长，无法直接观察金刚石→石墨的转变，这种转变发生在纳秒到皮秒的时间尺度上，如果发生的话。本文利用分子动力学（MD）和真实相互作用势，首次直接证明了金刚石-石墨转变确实发生，并可能是单点金刚石刀具在加工黑色金属材料时的主要磨损机制。为了研究金刚石刀具在100 m s（1）切削速度下纳米切削（100）取向纯铁和沿着（100）方向切削（110）、（111）和（100）取向纯铁的微观磨损机理，进行了金刚石刀具纳米切削（100）和沿（100）方向切削（110）、（111）和（100）取向纯铁的分子动力学模拟。Fe-Fe和Fe-C相互作用采用修正的嵌入原子（MEAM）势，C-C相互作用采用Tersoff势。计算采用了桑迪亚国家实验室开发的大规模原子/分子大规模并行模拟器（LAMMPS）软件。结果提供了第一个直接证据，即随着切削开始，在铁的存在下，在切削刃处的金刚石结构开始从金刚石立方转变为六方石墨。在这种转变之后，石墨碳扩散到铁中。发现金刚石（100）面对石墨化的抵抗力最大，（011）面对石墨化的抵抗力最小，（111）面显示出向石墨结构转变的中等倾向。这些结果与文献报道的实验观察结果雅阁。因此，MD观察结果提供了支持文献中提出的磨损机制的直接证据。(C)2008年由Elsevier B. V.出版。
It is well known that although diamond is life hardest known material, it cannot be used effectively for machining pure iron or low carbon ferrous alloys due to extremely rapid tool wear. Several research groups have postulated that the mechanism for the observed wear of diamond tools involves the initial transformation of tetrahedral diamond into hcp graphite. the thermodynamically more stable form of carbon under the usual conditions of machining/grinding. The next step in the postulated mechanism involves the diffusion of graphitie carbon into the iron workpiece. In spite of the wealth of publications reporting experimental investigations of this phenomenon, this proposed mechanism still remains no more than a hypothesis, albeit, a reasonable one. The problem is that the lime scales (a few seconds to a minute or more) over which the experiments are conducted are too long to permit direct observation of the diamond -> graphite transformation, which occurs on a nanosecond to picosecond time scale, if it occurs at all. In this paper, We utilize molecular dynamics (MD) and realistic interaction potentials to provide the first direct evidence that the diamond -> graphite transformation does Occur and, therefore, could be the principal mechanism of wear of single-point diamond tools in the machining of ferrous materials. MD simulations of nanometric cutting of pure iron oriented in (100) and cut along (100) direction have been conducted in different orientations of the clearance face, namely, (110), (111), and (100) with a diamond tool at a cutting speed of 100 m s (1) to investigate the micromechanism of diamond tool wear. A modified embedded atom (MEAM) potential was used for the Fe-Fe and Fe-C interactions, and a Tersoff potential for the C-C interactions. The computations employed the large-scale atomic/molecular massively parallel simulator (LAMMPS) software developed at the Sandia National Laboratory. The results provide the first direct evidence that as cutting commences, the structure of diamond at the cutting edge begins to transform from diamond cubic into hexagonal graphite in the presence of iron. Subsequent to this transformation, the graphitic carbon diffuses into the iron. The diamond (100) plane was found to be the most resistant and the (011) plane the least resistant to graphitization with the (111) plane showing intermediate propensity for transformation to a graphite structure. These results are in accord with reported experimental observations. Thus, the MD observations provide direct evidence supporting the wear mechanisms that have been proposed in the literature. (C) 2008 Published by Elsevier B.V.