The corrosion behavior of two cast Fe-xCr-5Si (x = 0, 5 at.%) alloys has been studied at 800. C inH(2)-CO2-H2S mixture. The addition of 5 at.% Cr improved the corrosion resistance of the Fe-5Si alloy by forming a protective scale of mixed Cr2O3 and SiO2 at the bottom of a non-uniform scale. The corrosion resistance of the cast Fe-5Cr-5Si alloy was further improved by a magnetron-sputtered film of identical composition that promoted the formation of a protective scale of a Cr2O3-SiO2 mixture at the coating/alloy interface. The mechanisms of forming the protective scales are examined and analyzed. (C) The Author(s) 2017. Published by ECS. All rights reserved.