Effect of Ni/C on the mechanical properties and microstructure of synthetic diamond brazed with Ni-Cr brazing filler metal

Ni-Cr brazing filler metal containing varying amounts (0 wt%, 3 wt%, and 5 wt%) of nickel-coated graphite (Ni/C) was employed to prepare brazed synthetic diamond samples. The interfacial microstructure characterization and thermal damage of brazed synthetic diamond were investigated using scanning electron microscope and Raman spectroscopy. The mechanical properties of static pressure strength and impact toughness of brazed synthetic diamond were investigated in accordance with the machinery industry standard. The hardness of brazed layer was measured using a micro-hardness tester. The results demonstrate the presence of lamellar compounds Cr₃C₂ and void columnar compounds Cr₇C₃ , as well as filamentous eutectic graphite, on the surface of brazed synthetic diamond following aqua regia corrosion. Increasing the Ni/C ratio in the Ni-Cr brazing filler metal leads to a reduction in graphitization degree of synthetic diamond. When the Ni-Cr brazing filler metal contains 5 wt% Ni/C, the compressive stress in brazed synthetic diamond is reduced by 65 MPa, the static pressure strength and impact toughness of brazed synthetic diamond are increased by 15.1% and 29.9%, respectively, and the hardness of brazed layer is decreased by 79 HV, this is beneficial to enhance self-sharpness of synthetic diamond tools brazed with Ni-Cr brazing filler metal. (author)