The Effect of Carbon Additions on the Creep Resistance of Fe-25Al-5Zr Alloy
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TRODUCTION
THE intermetallic alloys based on the compounds Fe3Al and FeAl are prospective candidates for high-temperature structural applications.[1–3] Alloying by refractory metals continues to be the most attractive way toward improvement of their mechanical properties.[4–11] Several methods can be adopted to enhance limited creep resistance: these consist mainly of adding elements for either solid solution strengthening or precipitation strengthening.[12,13] The precipitation strengthening is determined by the low solubility of the added elements. From this point of view, the alloying by zirconium may be of interest because nearly no solid solubility for Zr exists in the Fe-Al phases. The beneficial effect of zirconium addition on creep resistance was first reported for the Fe-28 pct Al-based alloy (at. pct is given throughout) by McKamey et al.[14–16] and the Fe-40 pct Al-based alloy by Whittenberger et al.[17] Moreover, a positive effect of a dispersion of fine Zr-rich carbides was demonstrated via microstructural analysis.[14] Subsequent studies focused on the additions of various amounts of zirconium to a wide range of Fe-Al alloys.[18–24] Less attention has been devoted to the combined additions of zirconium and carbon. The results of these studies are summarized elsewhere.[25] Carbon content appears to be FERDINAND DOBESˇ, Senior Researcher, is with the Institute of Physics of Materials, Academy of Sciences of the Czech Republic, ZˇIzˇkova 22, 616 62 Brno, Czech Republic. Contact e-mail: dobes@ ipm.cz VEˇRA VODICˇKOVA´, Senior Assistant Professor, is with the Department of Material Science, Faculty of Mechanical Engineering, Technical University of Liberec, Ha´lkova 6, 461 17 Liberec 1, Czech Republic. JOZEF VESELY´, Junior Researcher, and PETR KRATOCHVI´L, Professor, are with the Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 5, 121 16 Prague 2, Czech Republic. Manuscript submitted March 24, 2016. Article published online September 21, 2016 6070—VOLUME 47A, DECEMBER 2016
beneficial in suppressing the hydrogen embrittlement at grain boundaries.[26] The effect of the additives Zr (0.2 to 0.3 pct) and C (0.2 to 0.6 pct) on the phase composition and high-temperature mechanical properties of Fe3Al-type alloys was investigated in our previous paper.[25] It was shown that the ratio of zirconium to carbon additives influenced the phase structure and played an important role in determining the mechanical properties. The purpose of the present paper is to examine the influence of larger carbon additions (up to 3.5 pct) on the compressive creep of Fe-25Al alloy with similarly increased zirconium content (5 pct).
II.
EXPERIMENTAL
The examined alloys were prepared by vacuum melting and casting; Zr was added in metallic form. The dimensions of the cast ingot of the low-carbon alloy were 20 9 40 9 150 mm3. The casts of alloys with added carbon measured 10 9 15 9 30 mm3. The chemical compositions are listed in Table I. Some samples were additionally annealed at
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