Influence of brazing time on microstructure of high temperature brazing diamond with Ni-Cr alloy

Samples of high temperature brazing diamond with Ni-Cr alloy are prepared in protective atmosphere furnace for brazing time is 1 minute, 2 minutes, and 5 minutes. The microstructures were analyzed with Scanning electron microscope, energy dispersive spectroscopy and X-ray diffraction. The results show that there are two layers of carbides on the surface of diamond, lamellar carbide Cr3C2 and columnar carbide Cr7C3, the growth direction of Cr3C2 has a certain orientation relationship with the crystallographic plane of diamond, and Cr7C3 nucleates on the surface of Cr3C2. With the increase of brazing time, the morphology of carbide Cr3C2 turns from linear to lamellar and carbide Cr7C3 turns from granule to columnar. After brazing, chemical metallurgical combination is achieved between diamonds and brazing alloy and carbides are the primary reason for the strong bond strength.