Dissimilar joints have been used in various industries to reduce costs and improve the performance of equipment and structures. Bonding of stainless steels to nickel-based superalloys can be widely used in the oil and gas, refining and chemical industries. The aim of this study is transient liquid phase (TLP) bonding of Inconel 625 alloy to 316L stainless steel using the Cu interlayer. For this purpose, TLP process was performed at temperatures of 1080, 1100 and 1120℃ with durations of 15, 30 and 60 minutes. Microstructural studies, phase transformations and mechanisms, kinetics and thermodynamics of diffusion of Cu element from the interlayer to base metals using field emission scanning electron microscopy (FESEM) equipped with X-ray energy scattering spectroscopy (EDS), transmission electron microscopy (TEM), Light microscopy and X-ray diffraction (XRD) were performed. In addition, the diffusion of Cu element into base metals was simulated using MATLAB finite element software. The results showed that the best bonding was achieved at 1120℃ for 30 minutes. By increasing the bonding time to 60 minutes at a temperature of 1120℃ microvoids were formed in the bonding zone. The results of EDS analysis showed that the diffusion rate of Cu element in base metals decreases with increasing bonding time due to the growth of base metal grains and consequently the reduction of grain boundaries per unit volume. Mo-Nb, Cr-Mo and Nb rich precipitates in the diffusion affected zone of Inconel 625, Mo-Nb and Nb rich precipitates in the bonding zone and Cr-Mo and Nb rich precipitates in the diffusion affected zone of the 316L stainless steel were formed. Comparison of 316L/Cu/IN625 bond simulation results showed that the diffusion of Cu in 316L stainless steel in the simulation results was less than the experimental results, while the Cu diffusion in the Inconl 625 side in the simulation results was higher than the experimental results. The calculation results of the Cu atoms flux to the base metals showed that the diffusion of Cu towards the base metal of Inconel 625 is 30 times the diffusion on the 316L stainless steel side, which causes the shift of the bonding joint to the base metal of 316L stainless steel. In order to eva‎luate the mechanical properties of the joint, the shear strength of the joints and the microhardness changes in the joint were measured and the failure surfaces were investigated. Maximum shear strength (475MPa) and maximum microhardness (160VHN) were obtained in the bonded sample at 1120˚C for 30 minutes, which was in good agreement with the results of microstructural studies. Potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution were performed to eva‎luate the corrosion resistance of joints. The results of electrochemical tests showed a correlation between the results of microstructural tests and corrosion resistance of the joint. The sample given at 1120℃ for 30 minutes had higher charge transfer resistance and lower corrosion current density than other joints. The reason for the higher corrosion resistance in this sample is the diffusion of Cu towards the base metals and the reduction of the joint area width.

مرتضي شمعانيان، علي اشرفي

مسعود عطاپور، مسعود مصلائي پور، همام نفاخ موسوي