Brazing YAG ceramic to Kovar alloy with Ag–Cu–Ti filler alloy: Wettability, microstructure and mechanical properties

YAG ceramic was brazed to Kovar alloy under a high vacuum of 6–8 × 10−4 Pa. A good contact angle (θeq = 10.7°) was obtained by wetting AgCuTi filler metal on the YAG ceramic substrate, and the associated interfacial microstructure was characterized. The microstructure of the achieved YAG/Kovar joints brazed by AgCuTi filler was characterized by SEM, TEM and XRD, which was found to be YAG/Y2O3/(Fe, Ni)Ti/Ag(s, s) + Cu(s, s)/Fe2Ti + Ni3Ti/Fe2Ti/Kovar. The effects of different brazing temperatures on the joint structure were investigated. The thickness of the (Fe, Ni)Ti reaction layer increases, and the banded structure formed by Fe2Ti and Ni3Ti intermetallic compounds (IMCs) widens with increasing brazing temperature. Nanoindentation and shear tests were used to characterized the mechanical properties of the joints. As the brazing temperature increased, the shear strength of the joints first increased and then decreased. A joint with an optimal shear strength of 51.3 MPa was obtained at 870 °C for 10 min. The nanoindentation test reveals the obvious differences in mechanical properties between phases: (Fe,Ni)Ti phase has higher Young's modulus and hardness than Fe2Ti–Ni3Ti phase and Ag–Cu eutectic.