Preparation, Structure, Properties And Applications Of Titanium Coating On Diamond Abrasive

The bonding between diamond and many substrates may be realized through the metallization of diamond surface. An effective method is to coat diamond with carbide forming metal, titanium. However, traditional physical vapor deposition (PVD) or chemical vapor deposition (CVD) process cannot coat large quantities of particles each time. A new method, which is called vacuum slow vapor deposition, is developed in the present investigation. Titanium deposits homogeneously on the diamond surface to form Ti (TiC) coating through heating the mixture of diamond particles, Tids and TiH2 powders in vacuum. The gas environment surrounding per diamond particle makes this process especially propitious to large scales industrial deposition.Thermodynamics analysis results show that the equilibrium vapor pressure of TiCls(s) is above the system pressure at the depositing temperature of 923-1073 K, so it is assured that TiCls evaporates during the process. The changes of Gibbs free energy of TiHi decomposition and TiC forming reactions are both negative. Above results indicate that TiC may form during vacuum slow vapor deposition. The desired coating structure can be obtained by controlling the system pressure. The calculated activation energy of TiC forming is about 94 +7 kJ/mol.The structure characteristics of Ti-coated diamond are investigated by means of AFM, SEM, TEM and XRD. The results show that the content of TiC in the coating increases with the rising of depositing temperature, so does the C/Ti ratio of TiC. According to Grazing Incidence X-ray Diffraction (GIXD), the C/Ti ratio decreases from inside to outside of the coating and the layer structure of diamond-TiC-Ti forms. (100) plane of TiC grows preferentially on (100) plane of diamond crystal. TEM observations show that TiC first nucleates and grows at twins and dislocations on nano-crystal diamond surface.The results of the single grit compressive strength measurement show that the compressive fracture strength (CFS) of diamond improves after coating with titanium at the temperature of 973-1023 K and the maximum increment reaches about 20%. The strength increment declines due to the magnetic inclusions. Diamond thermal damage occurs at above 1073 K. The interface bonding strength between diamond and the coating increases with the rising of depositing temperature and reaches above 150 MPa after coating at 1023-1073 K for Ih. The interface bonding strength decreases while thedepositing temperature is higher than 1073 K. Thus the optimum depositing temperature is 1023-1073 K. The coating also can protect diamond from oxidizing. The start oxidation temperature of coated diamond grits reaches as high as 1230 K.Three-point bending experiment is taken to measure the bending strength of metal bond diamond blade. In comparison with uncoated diamond, the bending strength of Ti-coated diamond blade improves dramatically. The theoretic calculation shows that the bonding strength between diamond and the bond increases by 149 MPa owing to the coating.The industrial application confirms that applying the coated diamond in metal bond tools changes the wear stages of the diamond on the working face. The percentage of pull-out grits decreases greatly, while that of the well or micro-fracture grits increases. The protrusion height and the retained strength of diamond in tools increase as well. All these lead to prolonging the tool life. When Ti-coated diamond grits are used, the cheaper ferrous-base bond and lower diamond grits concentration or finer diamond grits may be used to manufacture tools, which may remain the high level of cutting efficiency and tool life. As a result, the manufacturing cost of diamond tools is reduced.