Interfacial Bonding Strength Between Brazing Alloys and CVD Diamond

Three groups of brazing alloys were compared in brazing chemical-vapor-deposited (CVD) diamond, including two nickel-based alloys (Ni-3Fe-7Cr-3B-0.5Si-0.02C and Ni-14Cr-10P-0.02C), one copper-based alloy (Cu-10Sn-15Ti), and two silver-based alloys (Ag-5Cu-1Al-1.25Ti and Ag-34.25Cu-1In-1.75Ti). The nickel-based alloys catalytically transformed the sp³-bonded diamond into sp²-bonded carbon during high-temperature brazing operation though with the existence of Cr as the active metal. The bonding strength was very low and the fracture primarily propagated through the sp²-bonded carbon. For Cu-10Sn-15Ti brazing alloy, the transformation of the sp³-bonded diamond into sp²-bonded carbon during high-temperature brazing operation was marginal. The bond strength was adequate and fracture took place primarily through the brazing alloy bulk, due to the high concentrations of Sn and Ti that caused the precipitation of abundant intermetallic compounds in the brazing alloy bulk. For Ag-based alloys having very low concentrations of Ti, no visible degradation of diamond was observed and the bonding strength was very high. Crack primarily propagated through the brazed interface or even the CVD diamond bulk.