Abstract: Brazing diamond tools has high protrude and strong bonding, while brazing process may cause much thermal damage to the diamond. Adding an appropriate amount of graphite into the Ni-Cr alloy is expected to prevent diamond graphitizing, and reduce the thermal stress of the diamond after brazing. The diamond is brazed at 1 050 ℃ using Ni-Cr alloy added 1%, 2%, 3%(wt) graphite separately in controlled atmosphere and held temperature for 5 minutes, then the surface micrographs and the interface microstructures of the samples are observed by scanning electron microscope and energy dispersive spectrometer. The result shows that the filler added 1% graphite has wettability, and the element of C from the graphite can react with the element of Cr to form the carbide, in which part of Cr3C2 can grow in nucleus on the diamond surface, and the growth direction of Cr3C2 has a certain orientation relationship with the crystal plane of diamond. The micrographs of Cr7C3 changes from solid into hollow and cluster graphite is formed in filler. The microhardness of the filler descends from 630 HV0.2 to 580HV0.2, which makes the diamond protrude easily when used.

Key words: controlled atmosphere brazing;diamond;Ni-Cr alloy;graphite;thermal damage