Interfacial microstructure and electrochemical behavior of diffusion welded joints of Zr-Alloy and super duplex stainless steel

Abstract

In this study, solid-state diffusion welded joints of zirconium alloy (Zr-Alloy) and super duplex stainless steel (SS) were prepared at 875 °C with varying welding times of 30, 45, 60, 75, and 90 minutes using a welding pressure of 4-MPa in a vacuum. The interface microstructure was characterized using optical, scanning electron microscopy in backscattered electron mode, and electron probe micro-analyzer. With 30 minutes of welding time, no intermetallic compounds were observed at the weld interface due to the minimum diffusion activity of chemical elements across the joints. However, for 45 minutes and above welding time, a phase mixture of ZrFe₂ + ZrCr₂ was observed near the interface of the welded joint, and the width of the phase mixture gradually increased with a further increase in welding time. The maximum joint tensile strength of ~ 302 MPa along with ~ 5.9% elongation was achieved in the joint developed for 45 minutes of welding time due to the formation of finely widened reaction products at the diffusion interface. The electrochemical studies of the welded joints were also investigated and a comparison was drawn between the same base metals using different electrochemical measurement techniques such as open circuit potential, electrochemical impedance spectroscopy, and potentiodynamic polarization in 0.1 mol/L HCl solution. It was identified that the corrosion rate of the welded joint made with 90 minutes welding time is the highest and the corrosion of the welded joints occurred in micro-galvanic mode due to the presence of intermetallic compounds at the joint interface.