Diffusion bonding of a cold-worked NI-base superalloy

Abstract

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 oC 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.