The Effect of Laves Phase (Fe,Al) 2 Zr on the High-Temperature Strength of Carbon-Alloyed Fe 3 Al Aluminide
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HE alloying by zirconium is a method to enhance HT mechanical properties of Fe3Al alloys. Very low solid solubility of Zr in the Fe-Al initiated investigations of the influence of Zr addition to Fe3Al and FeAl alloys. The beneficial effect of zirconium and niobium addition on e.g. creep resistance was first reported in papers by McKamey and Maziasz.[1–3] Significant attention was payed to the effect of Zr on the phase structure and high-temperature (HT) mechanical properties of iron aluminides. Especially the formation of Laves phase (Fe, Al)2 Zr and (Fe, Al)2 Nb was referred.[4–10] Aside are left the large additions of Zr (i.e., up to 30 at. pct[4,5]). It is important to determine the effect of carbon (present in the raw iron used for the preparation of iron aluminides for structural uses). This may modify the mechanical properties, corrosion process, etc., by the influence of, e.g., the Laves phase. The presence of carbon in iron aluminides with zirconium modifies the formation of Laves phase in the Fe corner of the ternary equilibrium diagram.[6] Low solubility of Zr in D03/B2 Fe-Al results in the formation of Laves phase (Fe,Al)2Zr. Recently, Kratochvil et al.[11] showed in iron aluminides alloyed by Cr that the ratio of zirconium and carbon influences the phase structure of Fe3Al-type alloys. This was documented by the effects of the ratio PETR KRATOCHVI´L, Professor, and ROBERT KRA´L, Associate Professor, are with the Department of Physics of Materials, Charles University, Ke Karlovu 5, 121 16 Prague, Czech Republic. Contact e-mail: [email protected]ff.cuni.cz VEˇRA VODICˇKOVA´, Associate Professor, and MARTIN SˇVEC, Ph.D. Student, are with the Department of Materials Science, Faculty of Engineering, Technical University of Liberec, Studentska´ 2, 46117 Liberec, Czech Republic. Manuscript submitted September 10, 2015. Article published online December 30, 2015 1128—VOLUME 47A, MARCH 2016
cZr/cC on both the yield stress 0.2 and the creep rate at high temperatures. Laves phase k1 (Fe,Al)2Zr and ZrC particles were found primarily along grain boundaries, with some distribution in the grains as well. Their strengthening role is limited to blocking the grain boundaries’ motion because the effect of these particles inside the grains (owing to large distance between the particles) was very small. Partly such effects of low concentrations of Zr and C have been mentioned by Kejzlar et al.[12] The appearing of metastable phases, (Fe1 xAlx)3Zr and Fe2Zr, which originate during the HT deformation[10] was also detected in the iron aluminides alloyed by Cr. It is therefore the purpose of the present paper to verify the effect of the ratio of zirconium and carbon—described by the difference cZr cC—in an alloy without chromium on the structures of Fe3Al alloys and on their HT yield strengths. The difference cZr cC was chosen as it better describes the amount of Zr left for the formation of Laves phase, if any, compared with the ratio of both concentrations. This fact is obvious from a significantly better correlation with eutectic (macC compared wit
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