Influence of tungsten coating on microstructure and thermal damage of brazed diamonds

ABSTRACTDegradation of diamond strength resulting from thermal damage in vacuum brazing process constrains the application of Ni-based brazed diamond tools. To reduce the thermal damage to brazed diamonds, the effectiveness of coating diamond with tungsten was investigated by scanning electron microscopy, Raman spectroscopy and friability test. Tungsten coating was deposited on diamond surfaces by vacuum diffusion method. The experimental results show that tungsten coating, as a buffering layer, plays a stress-relaxing role and brings about fewer cracks in the Ni-based matrix near diamond grains. Graphitization of W-coated diamond after brazing is much slighter than that of uncoated diamond and Ti-coated diamond, according to the morphology and Raman spectra. The isolation of diamond from nickel catalyst by tungsten coating inhibits the graphitization of diamond, which can further explain the increase in the toughness index of brazed diamonds.