Microstructure and Electrochemical Corrosion Properties of 316L Stainless Steel Joints Brazed with BNi5

Abstract

The study investigates the microstructure and electrochemical corrosion characteristics of 316L stainless steel joints brazed with BNi5. The experiment was carried out at 1150 °C and the holding time was 10 and 30 min respectively. The gap size was 30, 60 and 100 μm. The interface microstructures of the brazing joint were analyzed by Scanning Electron Microscopy (SEM) and the element composition was measured by Energy Dispersion Spectrum (EDS). The potentiodynamic polarization tests were conducted in the 3.5% NaCl solution using the CHI660E electrochemical workstation. The result shows that there are three zones in the brazing joint: Athermally Solidification Zone (ASZ), Isothermally Solidified Zone (ISZ) Diffusion Affected Zone (DAZ). A lot of Ni based solid solutions are formed in the ISZ and some intermetallics distribute in the solid solution layer parallel to the boundary. The ASZ is in the center of the gap, which contains eutectic structure and some brittle compounds. The Tafel curves reveal that the corrosion resistances of the brazing joints are poorer than base metal because the different phases in the joint form many micro batteries. With the decrease of gap size smaller or the increase of holding time, the corrosion resistance becomes better, because the longer holding time and smaller gap size are beneficial to the formation of Ni based solid solution with high corrosion potential.