Effect of alloying ratios and Cu-addition on corrosion behaviour of CoCrFeNiMo high-entropy alloys in superheated steam containing CO2, H2S and HCl

Highlights: • CoCrNiFeMo not prone to corrosionand thus shows potential for application in a high-temperature geothermal environment. • Thick Cu₂S corrosion film observed for CoCrNiFeMoCu high-entropy alloys in the testing environment. • Complex oxide layer observed under outer Cu₂S corrosion film on CoCrNiFeMoCu bulk alloy. • Cu rich intermetallics prone to corrosion between Mo rich and Ni-Fe rich phases in the CoCrNiFeMoCu high-entropy alloy. This article reports the morphology and corrosion study of CoCrNiFeMo and CoCrNiFeMoCu high-entropy alloys (HEA) tested in a simulated superheated geothermal environment to evaluate whether the alloys are candidate materials for a corrosive high-temperature geothermal environment. The HEA alloys with different alloying ratios were tested in superheated steam at 350 °C and 10 bar gauge containing HCl, H₂S, and CO₂ with acidic condensate (pH = 3). The Cu containing CoCrNiFeMoCu alloys were prone to corrosion damage and corrosion rate was accelerated by intermetallic Cu rich sites but the CoCrNiFeMo alloys were not prone to corrosion in the test environment.