Quality Analysis, Surface Metallization And Brazing Technology Research Of MPCVD Diamond Chip

Chemical vapor deposition （CVD） diamond chip cutting tools havehigh precision, high finish, long life and many other advantages. With thedevelopment of CVD diamond chip technology and cost reduction of itspreparation, diamond chip tools will gradually replace other tools. But in theexisting tool manufacturing process, the problem of bonding strength ofdiamond chip and the matrix still exists, which seriously affect theperformance of CVD diamond chip tools. Therefore it is necessary to studya new surface metallization process and brazing process to improve thebonding strength of diamond chip and the matrix.In this article, the quality of diamond chips of microwave plasmachemical vapor deposition （MPCVD） and DC arc plasma jet CVD methodswere compared. In order to study the mechanism, combined state of Moatom going into diamond and the effect of Mo atom on internal stress andsp²C content of diamond chip, plasma emission spectroscopy was measuredand the diamond chip was investigated with XPS, Raman and SEM. Theresults show that the impurity element content and internal stress ofMPCVD method for diamond chip are lower than that of the DC arc plasmajet CVD method for diamond chip. In the process of preparation of MPCVDmethod for diamond chip on Mo substrate, Mo atom can go into diamondchip by means of evaporating into plasma and exists with Mo⁺⁴、Mo⁺⁶ andMo⁺⁴-Mo⁺⁶ in the diamond. Along the nucleation surface to the growthsurface of MPCVD diamond chip, the content of sp²C gradually decreases.The internal stress is small and shows tensile stress on the nucleation surface.From about5μm near the nucleation surface, it is beginning to show compressive stress, and then gradually turns into tensile stress. It decreaseswith the increase of diamond chip thickness. The internal stress turns intotensile stress at about30μm near the nucleation surface and then increaseswith the further increase of diamond chip thickness.The oxide and carbide of Mo existed on the surface of diamond chipprepared on Mo substrate by MPCVD. Based on this phenomenon, theprocess of hydrogen plasma treatment and plating Ti on the nucleationsurface of the diamond chip were studied. The results show thatmolybdenum oxide on the nucleation surface can effectively be restoredgeneration corresponding carbide by hydrogen plasma surface treatment. Inaddition, the specific surface area and roughness of nucleation surface areincreased after hydrogen plasma surface treatment, which can improve theshear strength of brazed joint. With the power for800W, the hydrogen gasflow for135sccm, the pressure for14kPa, the temperature of diamond chipfor922℃and the processing time for120min, the hydrogen plasma surfacetreatment effect is best. Hydrogen plasma discharge treatment in lowpressure is necessary before plating Ti on the nucleation surface of thediamond chip treated by hydrogen plasma, which can effectively remove theoxygen in the vacuum chamber. After the temperature of Ti plate rises to1300℃to plate Ti120min, the Ti element mainly exists with metal, TiC andTiN on the nucleation surface. In this process of plating Ti, the shearstrength of brazed joint is best.Based on the diamond chip surface metallization, the process ofbrazing with high frequency induction heating in the air was studied. Theresults show that the shear strength of brazed joint is affacted greatly bydiffetent pretreatment methods on nucleation surface of the diamond chip,which is best after the process of hydrogen plasma surface treatment and plating Ti treatment. With a constant pressure in the whole process, thecontent of flux in brazing alloy for10%, brazing temperature for880℃,andholding time for15s, the shear strength of brazed joint is best, which canreach to174MPa.