Sulfidation behavior of an AlCoCrNiSi high-entropy alloy

High-entropy alloys (HEAs) are promising new materials considered for application in high temperature environments. In this work, the sulfidation behavior of an Al–Co–Cr–Ni–Si HEA at different elevated temperatures and various sulfur vapor partial pressures is investigated. Thermogravimetric studies indicate that the sulfidation kinetics are in accordance with the parabolic rate law. The corrosion rate has a strong temperature dependence, whereas the influence of sulfur vapor pressure is practically nonexistent. Changes in temperature also do not seem to affect the sulfidation mechanism as evidenced by the Arrhenius correlation determined between the obtained parabolic rate constants and temperature. Combined SEM–EDS and XRD studies reveal the formation of a thick multilayer scale on the studied alloy, where the outermost relatively compact part is built of Co_0.5NiS₂ and CrAl₂S₄ while the inner, rather porous part also contains metallic inclusions, including Si near the scale/substrate interface.