Electrochemical behavior and microstructure of diffusion welding of zirconium alloy and super duplex stainless steel

In this study, the effect of welding temperature on interface microstructure, mechanical properties, and electrochemical behavior of diffusion welded joints (DWJs) of zirconium alloy (ZrA, Zr702 grade) and super duplex stainless steel (2205 duplex stainless steel grade) were investigated. Alloys were welded in a vacuum atmosphere at four different temperatures (800, 850, 900, and 925 degrees C) for 75 min under 4 MPa compressive pressure. The optical, scanning electron microscopy, electron probe micro-analyzer, and X-ray diffraction techniques were used to characterize the interfacial microstructure of the DWJs. Layers of intermetallics were formed along the welded interface at 850 degrees C and above welding temperatures. At 850 degrees C, a single reaction layer (phase mixture of ZrFe2+ZrCr2) was observed; however, bilayers (ZrFe2+ZrCr2 and Fe2Zr+FeZr3 phase mixtures), and triple layers (ZrFe2+ZrCr2, Fe2Zr+FeZr3, and beta-Zr+FeZr3 phase mixtures) were observed at the welded interface of the joints processed at 900 and 925 degrees C, respectively. Width of the reaction layer (phase mixtures) increases with an increase in the welding temperature. The DWJs processed at 900 degrees C reach the maximum joint strength of similar to 312 MPa along with similar to 6.4 % ductility. For corrosion analysis, studies of the base alloys and DWJs in 0.1 mol/L HCl and 0.1 mol/L NaOH solutions separately using electrochemical techniques, such as open circuit potential, electrochemical impedance spectroscopy, and potentiodynamic polarization were undertaken.