Oxidation and hot corrosion studies on Fe-based superalloy A-286 pulsed current GTA weldments in gas turbine environment

Abstract

Cyclic air oxidation and hot corrosion performance of pulsed current gas tungsten arc weldment (PCGTAW) of Fe-based superalloy A-286 are evaluated in the air and Na2SO4–7.5%NaVO3–5%NaCl molten salt at 700 °C. Thermogravimetric analysis is carried out to evaluate the corrosion kinetics of the weldments. Scanning electron microscope, energy dispersive spectroscopy, and x-ray diffraction methods are used to investigate the surface morphology, composition and phases of the air oxidized and hot corroded weldments. The depth of corrosion attack and distribution of alloying elements in the oxidized and hot corroded weldments are investigated at the cross sections using SEM microstructure and elemental mapping analysis. Some oxide scales spalling and sputtering are observed in PCGTA weldment in the molten salt environment during hot corrosion study which is not observed in air oxidized weldment at the end of 50 cycles. The hot corroded weldment shows a higher weight gain than oxidized weldment. Presence of molten salt increases the rate of corrosion. The cross-sectional analysis clearly explains, in both the cases higher oxidation rate is observed in the base metal zone.