Thermal cyclic test of alumina/kovar joint brazed by Ni–Ti active filler

Active brazing was used to join high purity alumina ceramic and Kovar alloy with nickel and titanium foils. A sandwich structure was observed in the solder, an α-Ti solid solution belt at mid part and two Ti2Ni intermetallics belts at sides. Thermal cyclic tests were undertaken for the brazed joints at temperature ranging from 200 to 600 °C. Shear strength of joints were tested before and after thermal cycles. The results showed that shear strength increased dramatically after 40 thermal cycles. The determination and calculation of residual stress in joints indicated that thermal cycles reduced residual stress in joints observably due to similar effects as annealing, and resulting in improved strength.