Effect of Pulse Current Frequency on Microstructure and Hot Corrosion Behavior of Tungsten Inert Gas-Welded Joints of N155 Superalloy

Thin sheets of N155 superalloy with Inconel 718 filler metal were welded using tungsten inert gas (TIG) process with different frequencies of the pulse current system. The present study aims to compare the hot corrosion resistance of the weld metal of samples with different frequencies in 90% Na2SO4-10% NaCl molten salt environment at 950±5 °C. The results of the hot corrosion test indicated that the sample with optimal frequency (240 Hz) could form the alternate protective layers (Cr2O3 and NiO) that prevented the interference of the iron element during the hot corrosion; therefore, the amount of damage to the substrate was reduced, and it made the parabolic rate constant (Kp) lower (up to 6h: 1.87 and after 6h: 0.186 (×10^(-10) g2.cm-4.s-1)) than other welded specimens. In other welded specimens, due to the formation of poor and rich areas of chromium and nickel key elements, resulting from elements segregation of welding solidification, the weld metal surface was not uniformly corroded and the iron element created porous and brittle Fe3O4 oxide layers.