Diffusion Bonding of a Cold-Worked Ni-Base Superalloy

Diffusion bonding was conducted on cold-worked Alloy 600. Cold-work of 50 % was applied prior to diffusion bonding in order to incite recrystallization and limit grain growth. Tensile testing was conducted at room temperature and 550 °C for evaluation of joint efficiency, while premature brittle failure at the bond-line was observed for most diffusion bonding conditions. It was found that such premature failure was related to a planar bond-line that indicated lack of grain boundary diffusion across the bonding surfaces. Additional application of post-bond heat treatments did not result in significant bond-line migration. Microstructural analyses revealed the existence of Cr-rich carbides and Ti-rich precipitates along the bond-line, which prevented bond-line migration by acting as pinning points.