Brazing of large synthetic diamond grits using graphene nanoplatelets reinforced Ni[sbnd]Cr composite fillers

In order to reduce the degree of graphitization and excessive embeddedness of the diamonds in the brazing. In this work, graphene nanoplatelets (GNPs) were introduced into the Ni[sbnd]Cr filler to form composite fillers, and a two-step brazing method was adopted to optimize diamond brazed joints, which included pre-brazing of Ni[sbnd]Cr composite filler powder on the Q235 steel and followed by vacuum brazing of diamond grits directly. Through pre-brazing, composite filler coatings well combined with Q235 steel were obtained, which mainly composed of Ni(Fe,Cr), Ni₃P and Cr₃C₂ phases. The brazing results showed that the diamond brazed joints with no defect and high diamond exposure were achieved. New carbides of Cr₃C₂, (Cr,Fe)₃C₂ and Cr₇C₃ formed on the surface of the brazed diamonds. The addition of GNPs not only reduced the graphitization and thermal damage of diamond, but also improved the wear resistance of the joints. As the GNPs content increased, the new carbides were refined and the optimal wear resistance with value of 0.264 g was obtained by Ni-Cr + 2% GNPs composite filler. This experiment provides a new direction for the development of composite filler for brazing diamonds.