Evolution of interface carbide diamond brazed with filler alloy containing Cr

Using filler alloy containing active Cr to braze diamond can form different carbides at the brazing interface that will substantially influence the bonding strength and performance of the diamond. A series of Ni-Cu-based or Cu-based filler alloy containing Cr were used to braze diamond at different temperatures for 5 min in vacuum furnace. The morphologies of the carbide formed on the diamond surface were analyzed by SEM and EDS. Results show that with the increase in the proportion Cu-P-Sn in Ni-based filler alloy, the melting point of the filler alloy reduces, and the thermal damage to the diamond gradually decreases. In addition, the carbide formed in interface becomes thinner and changes from being in disarray to being in order. The carbide unites into a thin layer when Cu-Sn-Cr was used as the filler alloy. However, when Cu, Sn, and Ni-Cr-B-Si alloys are used, the carbide becomes Cr7C3, which is compact and resembles a short rod. Furthermore, adding some C into Ni-based filler alloy reduces the dissolution of the diamond in brazing and affects the melting point of the filler alloy. Hence, the differences in the morphology of the interface carbide and the thermal damage to the diamond are mainly related to the ratio between Cu and Ni in the filler alloy.