Investigations on interface microstructure and strength properties of dissimilar tin bronze/superalloy diffusion bonded joints

Diffusion bonding of dissimilar metals QSn4-3 and GH34 by using a QSn6.5-0.1 interlayer has been conducted in this study. The purpose of the study is to investigate the interface microstructure and strength of the joints, and to demonstrate the feasibility of using another high Sn content tin bronze interlayer to fabricate a typical microstructure joint. Microstructure examinations show that a penetration structure is formed by using a QSn6.5-0.1 interlayer, and its feature is apparent. Also, prolonging the holding time is conducive to the forming of the penetration structure. Shear testing results show that the penetration structure formed in a diffusion bonded joint of QSn4-3 and GH34 enhances the joint strength to almost the same as the QSn4-3 base metal. The mechanism forming the penetration structure is as follows: Sn atoms diffuse faster than Cu atoms into GH34 causing more Sn atoms to aggregate at the GH34 grain boundary. When the bonding temperature reaches 950°C for a short time, the aggregated Cu alloys having higher content of Sn than 5.3wt.% will melt, and penetrate and disrupt some grains from GH34 base metal.