Effect of joining temperature and bonding time on evolution of interfacial microstructure and brazing properties for 4J29/Ag–27Cu–4Ga/4J29 brazed joint

Abstract As a new type of vacuum filler metal, the effect of heating temperature and holding time on the interfacial microstructure evolution and brazing properties of 4J29 kovar alloy (Fe–29Ni–17Co)/Ag–27Cu–4Ga filler/4J29 kovar alloy brazed joint was observed. The typical interfacial microstructure corresponding to joint brazed at 900 °C/10 min could be divided into three different types of regions including 4J29 substrate (γ phase)/Diffusion zone (Fe (s.s)+Ag (s.s)+Cu(s.s))/residual filler metal region (Ag (s.s)+Cu(s.s)). Block-shaped β-Cu solid solution (s.s) extensively scatter in brazing alloy and played a large part in dispersion reinforcement. Owing to Cu and Ga elements diffuse to the interface between the substrate and the filler metal, β-Cu (s.s) layers generated at brazing interfaces and intensified brazing interface. The shear strength of joint increased from 830 °C to 870°/10 min and 5min to 10 min/870 °C due to the interfacial reinforcement effect of β-Cu(s.s) layers. The shear strength decreased from 900 °C to 960 °C/10 min and 10 min–25 min/870° because of weakened dispersion reinforcement of block-shaped β-Cu (s.s) phases. The brazed joints obtained a maximum shear strength of 339.6 MPa at optimal brazing parameters.