Abstract
In this research, dissimilar transient liquid phase (TLP) bonding of the nano/ultrafine-grained 304L stainless steel to the Inconel 718 superalloy was studied using a BNi2 interlayer. The bimodal stainless steel was produced by a thermomechanical martensitic method consisting of 80 % cold rolling and reversion annealing. The bonding processes were carried out at 1050 °C for 5, 15 and 60 min. The microstructural evaluation of the 304L/IN718 joints revealed that the isothermal solidification was completed at the bonding time of 60 min. The Cr-Fe-Nb-borides and Fe-Ni-borides were observed in the diffusion affected zone (DAZ) of IN718 and 304L, respectively. The average microhardness values of the ASZ and DAZ, were markedly higher than those of the ISZ and the base metals. The 5-min and 60-min joints exhibited the lowest and highest amounts of shear strength, respectively. Evaluation of the fracture surface of the 5-min sample indicated a brittle fracture while the 60-min joint was pronouncedly ductile. Cross-section of the fractured samples implied that the 5-min bond fractured through the ASZ while the failure of the 60-min joint happened at the interface of 304L/joint zone. In addition to the dissimilar bonding, similar TLP bonding of 304L stainless steel was evaluated. The 304L nano/ultrafine-grained bonded samples indicated high density of the DAZ precipitates and shear strength compared to the 304L coarse-grained TLP bonded sample.
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