Inconel 625 and Hastelloy X are two commonly used solid‐solution‐strengthened superalloys, and the connection of them is inevitable in high‐temperature applications. Brazing is a commonly accepted joining method. In this study, the two alloys were vacuum brazed by sandwiching a BNi‐2 adhesive filler into them. A brazing temperature‐dependent cracking phenomenon, where the cracking ratio decreased from 50.73% to 7.09% when the brazing temperature was elevated from 1030°C to 1070°C, was observed at the junctions. It is found that the microstructures of the junctions are not uniform and are categorized into two main types, both consisting of Si‐denuded, Si‐rich, and medium Si regions. The cracks predominantly form in Type II microstructures in which the well‐aligned Si‐denuded zones are fully constrained by the surrounding Si‐rich regions. The formation of the unique microstructures is attributed to deep undercooling induced by fast diffusion of B, as supported by composition characterization and thermodynamic calculations. The cracking susceptibility and the proportion of each microstructure type are governed by the brazing temperature, which influences the extent and likelihood of deep undercooling. Critical discussion indicates that the crack initiation most likely occurs within the Si‐denuded regions rather than at the eutectic regions.
Zhao et al. (Thu,) studied this question.