Enhanced mechanical properties and thermal cycling stability of Al2O3-4J42 joints brazed using Ag–Cu–Ti/Cu/Ag–Cu composite filler.

This study investigates the mechanical properties and microstructure evolution of Al 2 O 3 -4J42 joints brazed using Ag–Cu–Ti (ACT) and Ag–Cu–Ti/Cu/Ag–Cu (ACTCA) fillers during thermal cycling from 0 °C to 500 °C. The reaction products between Al 2 O 3 and brazing filler of these two types of joints are mostly composed of Ti–O compounds, Ti 4 Cu 2 O and Al-based compounds. Brittle intermetallic compounds (IMCs) are observed in ACT joints, but not found in ACTCA joints. The reaction layer in ACT joints becomes thinner and discontinuous with thermal cycles, while that in the ACTCA joints hardly changes. Besides, the stress-induced cracks occur within the Al 2 O 3 ceramic near the Al 2 O 3 /filler interface in the ACT joints, but no crack is found in the ACTCA joints. The mechanical tests show that the ACTCA joints maintain at least 217%, 154% and 144% higher shear strength than the ACT joints at 0, 10 and 20 thermal cycles, respectively. The Cu interlayer with low yield strength releases stress through plastic deformation, meanwhile acts as a barrier to prevent elements diffusion and the formation of the brittle IMCs, thus improving the mechanical properties and thermal cycling stability of the joints. [ABSTRACT FROM AUTHOR]