Transient liquid phase bonding of FSX-414 superalloy at the standard heat treatment condition

The as-cast samples of FSX-414 Co-based superalloy were heat treated at the standard solution and aging heat treatment cycles. Specimens for joining were cut from the as-cast ingot. Transient liquid phase (TLP) bonding was carried out at the standard solution cycle, using MBF-30 interlayer. Also, bonded specimens were homogenized at the standard aging condition.The microstructure of the as-cast, heat treated and TLP bonded specimens were studied. These studies showed that the non-uniform distributed carbides of the as-cast specimen were replaced by uniform ones during the heat treatment. Eutectic M23C6 carbides were observed in all specimens. Due to the complete isothermal solidification, no eutectic structure was observed in the bond region of bonded specimens. In the diffusion affected zone (DAZ) of these specimens, some intermetallics of the CoB system were seen. Line scan EDS analysis across the bonding zone of the homogenized joint showed more uniform distribution of alloying elements in comparison with the unhomogenized joint.Hardness profiling across the bonding zone showed that isothermal solidification zone's (ISZ) hardness in the homogenized specimen is closer to the base metal (BM) hardness in comparison with the unhomogenized specimen. A hardness peak was observed in the DAZ region of the both homogenized and unhomogenized joints. Shear strength and shear fracture energy of the homogenized joint were about 93% and 82% those of the base metal, respectively. More fibrous zones and smaller dimples were observed at the homogenized joint's fracture surface, in comparison with the unhomogenized one.

► Observation of eutectic M23C6 carbides at heat treated microstructures.
► TLP bonding and homogenizing at the standard solution and aging cycles.
► Close hardness of isothermal solidification zone to the base metal hardness.
► More uniform distribution of solute elements across bonding zone after aging.
► Shear strength of bonded + homogenized specimen about 93% of the base metal.