Diffusion and wetting behaviors of Ag nanoparticle and Ag nanowire pastes for laser brazing of Inconel 718

Ag nanomaterials have been investigated as a filler material for brazing Inconel 718 well below the bulk melting temperature of Ag using both vacuum and laser brazing. However, Ag nanoparticles and Ag nanowires exhibit different bonding strengths. In this study, we focus on different diffusion and wetting behaviors of two kinds of nanopastes. At 550 degrees C, the areal coverage of the nanopaste decreases as a result of shrinkage in the nanopaste. The shrinkage is followed by rapid wetting and spreading on the Inconel 718 surface. A deeper investigation to the diffusion behavior of Ag nanoparticle and Ag nanowire pastes during laser brazing provides a clear correlation between the diffusion distance and the bonding strength. The diffusion of the base material into the Ag joint is shown to result in a concentration "hump" near the Ag-Inconel 718 interface of different base material elements which is likely caused by a difference in diffusivity of Ag and the Inconel 718 constituent elements. Ag NW joints were found to have a thicker diffusion zone, but also exhibit some Nb/Mo segregation when brazed using 300-W laser power. This may lead in different metallurgic bonding.