Diffusion brazing of Nicrofer 5520 (IN-617) superalloy using an amorphous Ni-Cr-Si-B interlayer: Microstructural characterization and mechanical properties

Abstract

The applicability of the diffusion brazing technique for bonding Nicrofer 5520 superalloy was assessed. The experiments were carried out at 1120◦C for 5, 15, 20, 45, 90, 120, and 240 min holding times using 30 μm thick Ni-7%Cr4.5%Si-3.1%B interlayers. The microstructure, shear strength, and microhardness of the resultant joints were investigated. The results showed that the complete isothermal solidification (CIS) occurred after 20 min-holding time. The (Mo, Cr, Ni, Fe)-rich carbides and (Cr, Mo)-rich borides with various morphologies were observed in the diffusion-affected zone (DAZ). Before CIS, a Ni-rich boride and Ni-rich silicide along with Cr and Mo-rich borides were also detected in the centerline. After CIS, the volume fraction of precipitated phases in the DAZ region was reduced by increasing the holding time. Simultaneously, the chemical composition became more uniform; also, the shear strength of the specimens was improved, and for the 240 min-holding time, it reached about 93 % of that of the base metal. K e y w o r d s: Nicrofer 5520, diffusion brazing, bonding time, microstructure, mechanical properties