Microstructure and mechanical properties of Ni foam/stainless steel joint brazed using Ni-based alloy

An open-cell Ni foam and 304 stainless steel (SS304) were brazed using a Ni based-alloy (MBF20) as a metallic glass brazing filler by varying the brazing temperature (1030–1090 °C) and dwell time (0–60 min). Microstructures and mechanical properties of the joints were investigated to determine the best brazing conditions. When the brazing temperature was low and the dwell time was short, Ni foam was partially reacted with the filler metal in the Ni strut providing a good bonding strength. At higher bonding temperature and/or longer dwell time, a large amount of α-Ni and Ni3B phases were developed in the strut as B in the filler metal diffused into Ni strut. The size of Ni3B and its area fraction were increased with increasing temperature and time. In this stage, it was observed that cracks were readily initiated and propagated perpendicular to the tensile direction through interconnected Ni3B intermetallic compound resulting in degradation of fracture loads and % elongation. Based on the results, a set of acceptable dwell temperature-time couples were determined to the required bonding strength.