Abstract
Natural diamond has been brazed to Fe-42Ni alloy sheet using Ag-Cu eutectic filler including active metal of 4.5 wt% Ti, in order to investigate on the relation between the segregation behavior of the active metal to the brazed interface and the joint strength.
The examination of the effects of brazing thermal cycles on the reaction products and titanium segregation behavior at the diamond-filler interface showed that the microstructures at the interface were dendrite and cell structure in case of cooling rate of 12 K/sec and 1.5 K/sec respectively, and that the active metal (Ti) was not detected by EDS in the both structures. This suggests that titanium segregation at the joint interface and the grain boundaries occurs as a result of exclusion of titanium out of Ag-Cu eutectic crystals accompanied by the crystal growth.
The joints were fractured at the interface between diamond and brazing filler using a developed tensile shear test method to get the joint strength and the fractured surfaces at the interface. The strength of the joint made by the cooling rate of 1.5 K/sec was higher than that made by the rate of 15 K/sec. The disregistry values were also calculated from the mismatch of surface orientations and lattice constants at the bonded interface. The results showed that the disregistry of diamond and TiC to Ti were remarkably larger than those to Cu and Ag, which corresponded to the joint strengths and the fracture paths.
