Hot Corrosion of Cobalt-Based Alloy with (Na, K)<sub>2</sub>SO<sub>4</sub> Coating at 900 °C

Abstract

The hot corrosion behavior of pure Co, Co-10Cr and Co-10Cr-5Al alloys coated with (4～4.5) mg/cm2 (Na, K)2SO4 deposits has been studied at 900 °C in air by thermogravimetry and SEM/EDX analysis. The results show that hot corrosion rate of Co-10Cr alloy was obviously higher than that of Co-10Cr-5Al alloy and hot corrosion rate of pure Co was between those of the two cobalt-based alloys. Both alloys produced complex corrosion scales, containing an outermost layer of pure cobalt oxide and an inner layer where the oxides of both alloy components were simultaneously present on the Co-10Cr alloy, while a middle layer containing CoO and Cr2O3 and an inner layer of Al2O3 with a few aluminum sulfides appeared on the Co-10Cr-5Al alloy. The results were interpreted by taking into account the effect of active element and hot corrosion mechanism.