Hot corrosion behavior of silicide coating on an Nb–Ti–Si based ultrahigh temperature alloy

• Uncoated and silicide coated Nb–Ti–Si alloy were corroded in Na2SO4–NaCl molten.
• A thick and porous corroded scale was obtained for the bare alloy.
• The corrosion products of bare alloy are NaNbO3, Na2Nb4O11 and amorphous silicates.
• The silicide coating shows a porous and cracked NaNbO3 + Na2TiSi2O7 inner layer.

Hot corrosion behavior of an Nb–Ti–Si alloy and its silicide coating in Na2SO4–25 wt.% NaCl molten salts at 900 °C was investigated. For the bare alloy, a thick and porous corroded scale (Na-containing oxides) was formed after hot corrosion. The silicide coating showed a good oxidation resistance at 900 °C, while the presence of the molten salts aggravated the damage process of the silicide coating by forming a thick corroded scale which mainly consisted of a Na2TiSi2O7 outer layer and a porous and cracked NaNbO3 + Na2TiSi2O7 inner layer. The possible hot corrosion mechanism of the silicide coating has been explored.