High-temperature oxidation of Fe-Cr-Al-Si alloys extruded into honeycomb structures |
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Authors: | Tsuneaki Ohashi Takashi Harada |
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Affiliation: | (1) Corporate Resaerch and Development Group, NGK Insulators, Ltd., 2-56 Suda-cho, Mizuho-ku, 467 Nagaya, Japan;(2) Automotive & Industrial Ceramics Division, NGK Insulators, Ltd., 2-56 Suda-cho, Mizuho-ku, 467 Nagoya, Japan |
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Abstract: | The oxidation behavior of Fe–20Cr–5Al–(0.5–5)Si and Fe–(12–20)Cr–(5–7)Al–(1–2)Si alloys extruded into honeycomb structures has been investigated at 1150°C in air for up to 500 hr. The oxidation weight gains decrease with increasing Si and Cr contents in the 5-Al alloys. Si additions are more efficient than Cr additions to reduce the weight gain. Increasing Si content in the 5-Al alloys suppresses the formation of an iron-chromium complex oxide, forming mullite and vitreous silica in the scale, although the location is not clearly indicated. The 5-Si alloy shows anisotropy in elongation of the honeycomb specimen during oxidation in the Fe–20Cr–5Al–xSi alloys, whereas alloying with Si and Cr does not improve the oxidation resistance of the 7-Al alloys significantly. These results are explained by Wagner's theory of a secondary getter. However, we point out additionally that the difference between Si and Cr in the Pilling-Bedworth ratio and the solubility of their oxides in the Al2O3 scale may contribute to the significant effect of Si additions. Finally, this paper demonstrates that the selected Fe–Cr–Al–Si honeycombs having walls 200 m thick show excellent oxidation resistance over 500 hr at 1150°C in air. The time to catastrophic oxidation is roughly proportional to the wall thickness in extruded honeycombs. |
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Keywords: | oxidation kinetics extruded honeycomb structures Si Fe– Cr– Al alloys weight gain growth stresses and elongation |
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