Thermo-Chemical Wear Mechanism of Diamond as a Tool Material

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Thermo-chemical process is considered to be an essential mechanism of wear of diamond cutting edge in ultraprecision metal cutting, because the cutting edge under attritious contact with workmaterial is inevitably subject to elevated temperature. To understand the wear mechanism, the simplified experiments simulating the wear process of cutting edge are carried out. Analyses on the behavior of chemical reaction between diamond and metal are also made based on the thermodynamics and quantum chemistry. The results of the experiments and analyses show that the thermo-chemical wear by oxidation on the diamond surface contacting with a metal is observed when it is heated under the condition that the metal can be oxidized and also the metal oxide can be deoxidized by diamond. The wear of diamond is also promoted by carbonization of the contacting metal or the diffusion of carbon atoms on diamond surface into the metal. Based on the analyses, the condition on temperature and oxygen partial pressure under which the diamond shows thermochemical wear can be predicted. Although it is difficult to prevent the wear of cutting edge due to the restriction in realistic condition of atmosphere attainable, the application of thermo-chemical process seems to be useful for the high efficiency polishing of diamond.