【正文】 own in . The crystal lattices near the diamond grit are distorted when the diamond grit cuts into the region including these crystal lattices is halfellipse in region is under the diamond grit and a bit left to the center o. And the major axis of the ellipse is in the same direction as the position of forces. Furthermore， this region moves left as the diamond grit slides. 31 As shown in ， A1+A2A3 ， where O1O2 represents the surface of the shows that the removal materials do not pole up on both sides of the groove materials are removed and form chips. It is a cutting process. Whereas， the existing A1 and A2 show that ploughing also this state is the cutting state acpanied by ploughing. 32 Microstructure of specimen after the grit sliding Section of the grooves in the longitudinal direction There are three key points in lapping， as shown in . Firstly， atoms near the diamond grit are forced to make some displacement from their initial crystal lattices including these atoms distort a boundary between the distorted lattices and the perfect lattices is along the diamond（ 111） surface（ the black lines） as shown in （ a） .The 33 displacements of the atoms bee bigger and bigger along with the diamond grit sliding and more atoms deviate from their initial lattices including these atoms distort phase transformation that the diamond cubic diamond transforms into amorphous graphite starts on a few atoms （ in the dark circles） at the end of this is to say that the hybridized orbit converts from sp3 to sp2. Secondly， the lattices below the diamond grit have the worst distortion and the boundary faceting along the（ 111） surface extend to the deeper layer， as shown in （ b） . More atoms transform from diamond cubic diamond to amorphous graphite ， especially those in the dark circle. Besides， some atoms are taken away by the diamond ， some lattices revert a little with the force minimizing， as shown in （ c） . However， the atoms which have the phase transformation cannot revert to their initial phase， especially those in the dark circle. Therefore， the groove is to the left on the surface of the diamond specimen. 34 Scattergrams of atoms in longitudinal section A in different states Bond formation From the simulation， it is found that the phase transformation is due to the flattening of the tetrahedron structure in diamond cubic diamond， as shown in position transformation at progressive time steps is demonstrated 35 in . Crystal cell of the diamond crystal lattice taken out from the circular region in （ a） As shown in （ a）， the tetrahedron is deformed when the grit slides close. And the deformation is serious when the grit cuts into section A， as shown in （ b） . The tetrahedron is flattened a after， the tetrahedron deforms badly， as shown in （ c） .Its four vertexes are almost on a plane and some bonds are broken. At the same time the phase transformation is acplished. Change of the tetrahedron marked in when the grit slides Pair correlation function The pair correlation functions of the specimen and the chip are shown in and curve in is syllabified to a lot of clear 36 peaks， which are the same as the diamond’s radial distribution fuction(RDF). However， there are only two peaks in , and the peaks are continued, which illuminates that amorphous exists in debris atoms. Therefore， it is sure that the phase transformation takes place in lapping. Pair correlation function of specimen atoms Pair correlation function of debris atoms XRD shows the Xray diffraction（ XRD） analysis of the debris produced in the lapping experiment. It demonstrates that the amorphous carbon， small 37 diamond particles or chips and FeC positions（ like Fe7C3 and Fe5C2）exist together in the debris. Consequently， the amorphous carbon is produced in lapping， which corresponds to the simulation result. XRD analysis of the debris produced in the experiment 3 Conclusions （ 1） A threedimensional MD model about the atoms of diamond cutting tools and diamond grit is built by using the molecular dynamics. Lapping at a special cutting depth is simulated. （ 2） The boundary of the transformation zone is regular ， faceting along （ 111 ） surface. The microcleavage only occurs inside this boundary. （ 3） Interaction between the diamond grit and diamond specimen leads to a phase transformation amorphous transformation appears as the grit 38 it is expounded from the parison between the bond formatting and pair correlation function. Moreover， it has also been proved in the lapping experiment. References： ［ 1］ Yuan Z J， Yao Y X， Zhou M， et al. Lapping of single crystal diamond tools［ J］． CIRP AnnalsManufacturing Technology， 2021， 52（ 1）： 285288. ［ 2］ Uegami K ， Tamamura K ， Jang K K. Lapping and frictional properties of diamond，and characteristics of diamond cutting tool［ J］． Journal of Mechanical Working Technology，1988， 17（ 8）： 147155. ［ 3］ Tolkowsky M. Research on the Abrading， Grinding or Polishing of Diamond［ D］． London： City and Guilds College， University of London， 1920. ［ 4］ Bowden F P， Tabor D. Physical Properties of Diamond ［ M］． Oxford： Clarendon Press， 1965. ［ 5］ Brezoczky B ， Seki H. Triboattaction ： Friction under negative load［ J］． Langmuir，1990， 6（ 6）： 11411145. ［ 6］ Couto M， van Enckevort W J P， Seal M， et al. Scanning tunneling microscopy of polished diamond surfaces ［ J］． Applied Surface Science， 1992， 62（ 4）： 263268. ［ 7 ］ van Bouwelen F M. Mechanically Induced Degradation of Diamond ［ D］ ． Cambridge ： University of Cambridge， 1996. ［ 8］ Grillo S E， Field J E， van Bouwelen F M. Diamond polishing： The dependency of friction and wear on load and crystal orientation［ J］． Journal of Physics D： Applied Physics，