The influence of Si on the primary protection of lean FeCrAl model alloys in O2 and O2+H2O at 600 °C—A microstructural investigation

Highlights: • The effect of Si on lean FeCrAl model alloys was investigated in O₂ and O₂+H₂O at 600 °C. • Significantly increased Al-content in the oxide scale in O₂ upon addition of Si. • Thermodynamic calculations propose that the presence of Si in the alloy, increases the activity of Al and reduce it for Cr. • Addition of Si prevented breakaway oxidation in O₂+H₂O. • Si-containing alloy displayed enrichment of Si and reduction of Cr-content in the oxide scale in O₂+H₂O. The present study investigates the influence of Si on the high-temperature corrosion behavior of lean FeCrAl model alloys in O₂ and O₂+H₂O at 600 °C. The addition of Si prevented breakaway oxidation in O₂+H₂O which may be explained by the increased Al-content and reduced Cr-content in the oxide (O₂) as well as the Si-enrichment in the outer part of the scale (O₂+H₂O). A proposed explanation for the impact of Si-addition on the Cr- and Al-content was given by thermodynamic calculations which showed that the presence of Si increases the activity of Al in the alloy while reducing the activity of Cr.