Insights into the hot corrosion of CoCrFeNi high entropy alloy in molten Na2SO4+25 %K2SO4 at 900 °C

Hot corrosion is the accelerated oxidation of salt contaminants such as (Na,K)2SO4 deposited on the turbine blade surface. This paper provides an insight into the potential application of CoCrFeNi high entropy alloy (HEA) as a hot corrosion-resistant alloy working at high temperatures. The hot corrosion behavior of CoCrFeNi HEA was investigated through mass gain, EIS, SEM, EDS, and XRD. The results show that the mass gain of hot corrosion increased in the first 20 h and decreased after 30 h due to a large amount of oxide film peeling off. The EIS comprised three capacitive loops before 4 h, and two capacitive loops after 6 h. It indicates that dis-continuous spinel oxide composed of multi-elements is rapidly formed on the surface of the alloy at the initial stage of hot corrosion, and a Cr-rich (Cr,Fe)2O3 layer is formed inside the alloy as time passes. The corrosion products for 10 h are mainly composed of porous (Fe,Cr,Co)3O4 spinel in the outer layer and Cr-rich (Cr,Fe)2O3 in the inner layer. As time approaches 100 h, the outer spinel layer peels off seriously. The primary corrosion product consists of (Fe,Cr,Co)3O4. The internal sulfide phenomenon occurs in the matrix.