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Vol.57, No.10, 648 ~ 656, 2019
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| Title |
| High-Temperature Corrosion of Ti-44Al-6Nb-2Cr-0.3Si-0.1C Alloy in 0.2%SO2/Ar Gas |
| 김성웅 Shi Yuke , 홍재근 Xiao Xiao , 한준희 Seong Woong Kim , 이동복 Jae Keun Hong , Junhee Hahn , Dong Bok Lee |
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| Abstract |
| Cast Ti-44Al-6Nb-2Cr-0.3Si-0.1C alloy having good air-oxidation resistance was corroded under 1 atm of flowing 0.2%SO2/Ar gas at 900-1100 oC for 50-300 h in order to examine its corrosion behavior in a SO2-containing environment, because SO2 is an industrially important by-product in the field of combustion and processing of fossil fuels. The corrosion rate in 0.2%SO2/Ar gas was faster than that in 0.2%O2/Ar gas, suggesting that sulfur deteriorated the corrosion resistance of the alloy. The scale consisted primarily of an outer TiO2 oxide layer with some α-Al2O3 islands, and an inner α-Al2O3-rich, TiO2-deficient oxide layer. Ti and Al, having strong oxygen affinities, preferentially oxidized to highly stable rutile-TiO2 and α-Al2O3 in the oxide scale. Small amounts of Cr and (Nb, Cr) dissolved in the outer and inner oxide layer, respectively. The outer oxide layer formed mainly by outward diffusion of Ti and Al, along with a lesser amount of Cr. The inner oxide layer formed by inward diffusion of oxygen and sulfur. The consumption of oxygen in the oxide scale facilitated the formation of Ti2S and Nb1-xS sulfides in the subscale. Oxidation and sulfidation prevailed in the oxide scale and the subscale, respectively. Sulfur migrated across the oxide scale into the subscale, where Nb, Cr, and Si accumulated to a certain extent due to their thermodynamic nobility when compared to Ti and Al. Although the alloy displayed good corrosion resistance in 0.2%SO2/Ar gas, microcracking and void formation in the oxide scale and subscale were unavoidable.
(Received July 8, 2019; Accepted August 27, 2019) |
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| Key Words |
| TiAl, intermetallics, oxidation, sulfidation |
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