Investigation of microstructure evolution of Inconel 939 joint diffusion brazed using an amorphous liquated Ni-Cr-Fe-Si-B interlayer

In this study, IN-939 high-chromium nickel-based superalloy was diffusion brazed using an amorphous Ni-Cr-Fe-Si-B foil as an interlayer and under high vacuum conditions. A successful joint was obtained at the applied temperature and bonding time of 1120 degrees C and 45 min. The microstructural evolution of the joint area was also investigated. The phases formed through the bonding process were categorized into three distinguished zones: isothermally solidified, athermally solidified, and diffusion-affected zones. According to the results, a gamma solid--solutionsingle-phase was produced in the centerline of the joint. Also, some precipitates with blockage and Widmanstatten morphologies were observed in the diffusion-affected area that appears to be Cr-rich borides. Chromium depletion occurred in the gamma matrix adjacent to these precipitates. In addition, the number of precipitates decreased, moving away from the interface of the isothermally solidified zone towards the base metal. The highest and lowest microhardness values were obtained for the DAZ and ISZ, respectively. The precipitation of hard Cr-rich boride particles in the DAZ and the absence of a second phase in the ISZ microstructure were probably responsible for this difference in the hardness.