Abstract
Transient liquid phase diffusion bonding was used to join stainless steel 304 with pure copper and aluminum foils as interlayers. The bonding process was conducted in a vacuum furnace at various temperatures and diffusion times. The joints were analyzed using optical and scanning electron microscopy, energy dispersive spectrometry, and microhardness measurements. Results indicated that the hardness of the bonds formed with the copper interlayer in a vacuum was higher than those formed with the aluminum interlayer. The poor mechanical properties of the bonds were attributed to the formation of intermetallic compounds within the bond region. Prolonged holding of the parent alloy at the bonding temperature likely led to complete isothermal solidification. The diffusion of the main elements from the interlayers into the base metal at bonding temperatures was the primary factor influencing the microstructural evolution of the joint interface. Selecting an appropriate bonding temperature to achieve the maximum concentration of melting point depressants depended on the duration of isothermal solidification. To assess the corrosion resistance of the joints, Tafel tests were conducted in a 3.5% NaCl solution. The presence of eutectoid γFe + eutectic Cu + Cr and Fe-Al intermetallics was detected at the interface of the joints bonded with copper and aluminum interlayers, respectively. The highest microhardness was observed in the diffusion zone, with hardness values gradually decreasing as the distance from the joint increased. The joints involving stainless steel and copper exhibited crevice corrosion due to the galvanic couple between the stainless steel and copper. Additionally, pitting occurred due to intergranular stress corrosion cracking on the copper surface.
