Effect of brazing temperature on the microstructure and mechanical properties of diamond/kovar joints

To obtain high quality brazed joint of diamond and kovar alloy, systematic work was conducted. Firstly, AgCuTi filler alloy was used for vacuum brazing of diamond to kovar alloy, and the microstructure of resulting joints was systematically characterized to elucidate the formation mechanism. Then, the effects of brazing temperature on joint microstructure and shear strength were investigated, and the correlation between microstructural evolution and shear strength was established. The results indicate that the AgCuTi filler alloy exhibits excellent wettability on the diamond substrate, with a contact angle (θ) of 2.7°. The microstructure characteristics of the diamond/kovar brazed joint are diamond/TiC+Ag(s, s) + Cu(s, s) + Fe₂Ti + Ni₃Ti/kovar. A maximum shear strength of 100.94 MPa is obtained at 870 °C with a holding time of 5 min. With increasing brazing temperature, the (Fe, Ni)Ti reaction layer thickens, the banded structure of brittle intermetallic compounds (IMCs) Fe₂Ti and Ni₃Ti broadens. This microstructural evolution initially enhances the shear strength but eventually leads to a decline due to excessive IMCs formation.