Abstract
In the present study, microstructure and the corrosion behavior of Nickel based superalloy 686 and its weld joints has been investigated by synthetic sea water environment. The weldments were fabricated by Gas Tungsten Arc Welding (GTAW) and Pulsed Current Gas Tungsten Arc Welding (PCGTAW) techniques with autogenous mode and three different filler wires (ERNiCrMo-4, ERNiCrMo-10 and ERNiCrMo-14). Microstructure and Scanning electron microscope examination was carried out to evaluate the structural changes in the fusion zones of different weldments. Energy Dispersive X-ray Spectroscopy (EDS) analysis was carried out to evaluate the microsegregation of alloying elements in the different weld joints. Potentiodynamic polarization study was experimented on the base metal and weld joints in the synthetic sea water environment to evaluate the corrosion rate. Tafel’s interpolation technique was used to obtain the corrosion rate. The microstructure examination revealed that the fine equiaxed dendrites were observed in the pulsed current mode. EDS analysis shows the absence of microsegregation in the current pulsing technique. The corrosion rates of weldments are compared with the base metal. The results show that the fine microstructure with the absence of microsegregation in the PCGTA weldments shows improved corrosion resistance compared to the GTAW. Autogenous PCGTAW shows higher corrosion resistance irrespective of all weldments employed in the present study.
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