Mechanical and microstructural characterization of dissimilar transient liquid phase (TLP) bonding between AISI 304 and 17–4PH stainless steels

• A bimetallic component composed of AISI 304 and 17-4PH stainless steels was successfully fabricated using TLP bonding. • All joints exhibited complete isothermal solidification, with no evidence of eutectic phases at the bond centerline. • Micro-voids attributed to the Kirkendall effect were observed in the ISZ at short holding times; these voids progressively diminished with increasing bonding duration. • Maximum shear strength was achieved at a bonding temperature of 1100 °C with a hold time of 75 minutes. In this study, the fabrication of nonmagnetic-magnetic bimetallic components from AISI 304/17-4PH stainless steels was investigated using the transient liquid phase (TLP) bonding method. Bonding was performed at different temperatures of 1050, 1100, and 1150 °C with holding times of 30, 45, 60, and 75 min using a boron-containing Ni-based (BNi-2) interlayer. Microstructural analysis revealed that isothermal solidification was completed with no indication of athermal solidification. In addition, some micro-voids were observed in the isothermal solidification zone (ISZ) near its interface with the diffusion affected zone (DAZ), and their size and density varied with bonding time and temperature. The results indicated that the shear strength of the joints was primarily influenced by: the concentration of strengthening elements (Fe and Cr) within the ISZ, pore characteristics, and the ISZ width. The highest shear strength was achieved at a bonding temperature of 1100 °C held for 75 min. Examination of the fracture surfaces of the shear strength test specimens revealed that, at a given temperature, increasing the bonding time caused a transition in the failure mode from non-ductile to ductile. Moreover, the microhardness results indicated that the hardness within the ISZ was governed by the competition between solute-induced strengthening and ISZ widening–induced softening. At the lowest bonding temperature (1050 °C), solute enrichment dominates, whereas at the elevated temperature (1150 °C), widening of the ISZ became the governing factor.