Microstructural evolution during low-temperature TLP bonding of Inconel 600 to copper for high-temperature service applications

Abstract

Transient liquid phase (TLP) bonding of Inconel 600 to copper was performed in an air atmosphere using a tin interlayer at 700°C for three different holding times of 5, 15, and 30 min. Prior to the bonding procedure, tin was soldered onto the Inconel600 bonding surface to displace the passive oxide layer as a wettability barrier. For samples processed for 5 min, various microstructures, including nickel solid solution ((Ni)_ss) + Ni₃Sn/(Ni)_ss/Ni₃Sn/copper solid solution ((Cu)_ss) + δ, were detected, which were replaced by copper and nickel solid solutions as the bonding time increased to 30 min. By prolonging the bonding time from 5 to 30 min, not only did the shear strength increase from 73 to 171 MPa but also, on the basis of differential scanning calorimetry, the remelting point of the solidified composition at the interface of the 30-min bonded samples reached 987.4°C (250°C greater than the bonding temperature), enabling the joint to be used for high-service-temperature applications.