Hot Corrosion Behavior of a Powder Metallurgy Superalloy Under Gas Containing Chloride Salts

Hot-corrosion behavior of a powder metallurgy superalloy (Alloy 1) under gas containing chloride salts at 700 °C, 750 °C and 800 °C were investigated via weight-gain measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron probe micro analysis (EPMA). The hot-corrosion behavior of a similar alloy (Alloy 2) at 800 °C and the same conditions were also carried out for comparison. The experimental results showed that the average mass gain of Alloy 1 increases as the temperature elevates. The corrosion kinetics followed linear power law at 700 °C, 750 °C and 800 °C. The corrosion layers obtained after 100 h of hot corrosion were mainly composed of Cr2O3, TiO2, Al2O3, NiO and NiCr2O4. The cross-sectional morphologies and corresponding elemental maps indicated that the chloride salts penetrated into the corrosion product and caused it to produce many cavities and cracks. According to these results, the hot corrosion of Alloy 1 under gas containing chloride salts is confirmed to be an accelerated oxidation process due to the damage in integrity of the oxide film caused by continuous corrosion with chloride salts. Compared to Alloy 2, the increased Co and Al content in Alloy 1 with better hot corrosion resistance at 800 °C promoted the rapid formation of continuous Cr2O3 and Al2O3 protective films on the alloy surface in which Co inhibited internal oxidation of Al through the third element effect.