Investigation of Effect of Cold Working and GTAW and PCGTAW Process Parameters on Corrosion Behavior of Nimonic ۸۰ super-Alloy

The purpose of this study is to examine the corrosion resistance of the Nimonic ۸۰ superalloy welded with ۶۲۵ filler metal using continuous and pulse welding strategies after cold working. The experiments using these strategies were divided into four cases with different cold work levels. Two specimens were welded using the continuous method, while two were welded with pulse welding. Cold pre-working (rolling) was applied to the specimens: ۲۵ and ۵۰% cold rolling for the continuous welded specimens, and ۵۰% cold work for the pulse-welded ones. Welding conditions included a constant current of ۱۰۰ A and ۱۲ V for the continuous method, while pulse welding used variable currents with peak/base combinations of Ip = ۱۵۰ A / Ib = ۵۰ A and Ip = ۱۲۵ A / Ib = ۷۵ A. X-ray diffraction (XRD) analysis identified phases like nickel, molybdenum, and titanium in the specimens. They were then tested in a ۳.۵ wt.% NaCl solution using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Results showed that specimens welded with both methods, including ۲۵% cold work in the continuous welds and ۵۰% cold work in pulse welds at ۱۵۰/۵۰ A, had the highest corrosion potential and the lowest corrosion current density. Cold working enhanced the thermodynamic and kinetic aspects of corrosion resistance, though its overall effect on the corrosion rate was minor. Impedance tests indicated that the specimens with ۲۵% cold work welded with the continuous method and those with ۵۰% cold work welded by pulse welding at ۱۵۰/۵۰ A had the highest polarization resistance and the lowest charge accumulation. Conversely, specimens with ۵۰% cold work welded by the continuous method and pulse welding at ۱۲۵/۷۵ A showed the lowest charge transfer resistance and the highest capacitive behavior.

کلیدواژه ها:

Nimonic ۸۰ superalloy ، corrosion ، Cold work ، GTAW