Chlorine-Induced High Temperature Corrosion of Inconel 625 Alloy with the Addition of Yttrium at 800 °C

Abstract

The chlorine-induced corrosion behavior of Inconel 625 alloys with the addition of 0- 1.0 wt.% Y has been investigated in N₂ - 1.0 vol.% HCl-1.5 vol.% O₂ -3.0 vol.% CO₂ mixed gas at 800 ° C for 200 h. The scale grown on Inconel 625 alloy was composed of a thin continuous layer of Cr₂O₃ in contact with the alloy, partly covered by a discontinuous layer of SiO₂ or even by isolated particles of SiO₂. However, the scales grown on Inconel 625-0. 1 wt.% Y, Inconel 625-0. 3 wt.% Y and Inconel 625-0. 5 wt.% Y alloys were almost entirely composed of a continuous Cr₂O₃ layer. Therefore, the three alloys were of better corrosion resistance, with the total mass gain less than a fifth of that of Inconel 625 alloy. Inconel 625-0. 1 wt.% Y alloy showed the best corrosion resistance, with the smallest mass gain of 0.09533 mg/cm² for 200 h. With further increases of Y content, Inconel 625-0.7 wt.% Y and Inconel 625-1.0 wt.% Y alloys did not obtain more satisfactory corrosion resistance. On the contrary, the protective performance of Cr₂O₃ layer declined and it could not effectively inhibit the outward evaporation of SiCl₄. The addition of a small amount of rare earth element Y can promote the formation of a protective Cr₂O₃ layer and thus improve the corrosion resistance of Inconel 625 alloy, but the amount should be controlled within a very small concentration range.

Keywords: Inconel 625 alloy, chlorine-induced corrosion, active oxidation, rare earth effect