Surface Characterization of Incoloy 825 Ni-Based Alloy/2507 Super Duplex Stainless Steel Dissimilar Friction Stir Welds

Abstract

Surface features of a dissimilar friction stir weld between Incoloy 825 Ni-based alloy and SAF 2507 super duplex stainless steel were investigated using scanning electron microscopy, microhardness test, cyclic potentiodynamic polarization, and electrochemical impedance spectroscopy. The surface of the weldment showed lower general corrosion resistance in comparison to the base metals. Areas under the weld shoulder exhibited weak pitting resistance because of the deformed structure and/or chromium nitride precipitates. Incoloy 825 located under the shoulder also displayed the highest susceptibility to pit growth because of the austenite matrix containing titanium nitride phases. Overall, the obtained results demonstrated that the friction stir welding method could significantly deteriorate the surface corrosion behavior of the processed regions.