The corrosion behavior of a sputtered micrograin film on Fe-5Cr-5Si alloy in H2-CO2-H2S mixture at 700 °C

•The as-cast Fe-5Cr-5Si alloy suffers a serious degradation in H2-CO2-H2S at 700 °C.•The sputtered Fe-5Cr-5Si film decreases the corrosion rate of the Fe-5Cr-5Si alloy.•A thin layer of SiO2 + Cr2O3 forms at the coating/alloy interface.•The formation mechanism of the protective SiO2 + Cr2O3 layer is discussed thoroughly.

The corrosion behaviors of as-cast Fe-5Cr-5Si alloy with and without sputtered Fe-5Cr-5Si film in H2-CO2-H2S mixture at 700 °C are studied. The corrosion scale forming on the as-cast alloy is non-protective and mainly composed of FeS outer layer and FeS + FeCr2O4 + Fe2SiO4 inner layer. However, a continuous Cr2O3 + SiO2 layer which possesses favorable protectiveness forms at the coating/alloy interface for the coated alloy, even though FeS layer and FeS + FeCr2O4 + Fe2SiO4 mixed layer also form. The formation mechanism of the Cr2O3 + SiO2 layer on the coated alloy is discussed thoroughly.