Strengthening of Fe 3 Al Aluminides by One or Two Solute Elements
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UCTION
ALLOYS based on iron aluminides Fe3Al show potential for structural applications at high temperatures owing to their excellent oxidation and sulfidation resistance. They display lower density compared to other iron-based materials, and their low cost is advantageous as well. Unfortunately, they also show unfavorable lack of room temperature ductility and low high-temperature strength.[1–5] During the last decades, research efforts have focused on enhancing the ductility, strength, and creep resistance of iron aluminides by alloying. Several approaches have been explored to improve the high-temperature mechanical properties of these alloys. Basically, solid solution hardening (SSH), strengthening by coherent and incoherent precipitates, and increasing the crystallographic order were considered for the strengthening of iron aluminides.[1,6–9] Elements such as Cr, Ti, Mn, Si, Mo, V, and Ni were added for SSH[2,10–12] and Palm[8] compared the SSH by Ti, V, Cr, and Mo at 873 K, 973 K, and 1073 K (600C, 700C, and 800 C). Recently, Kratochvil et al.[12] described the SSH effect of
PETR KRATOCHVI´L, PETER MINA´RIK, JOSEF PESˇICˇKA, and ROBERT KRA´L are with the Charles University, Faculty of Mathematics and Physics, Department of Physics of Materials, Ke Karlovu 5, Prague 2, CZ-12116, Czech Republic. Contact e-mail: [email protected]ff.cuni.cz STANISLAV DANISˇ is with the Charles University, Faculty of Mathematics and Physics, Department of Condensed Matter Physics, Ke Karlovu 5, Prague 2, CZ-12116, Czech Republic. Manuscript submitted June 3, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
vanadium in Fe3Al using the SSH theories for binary alloys of Fleischer[13] and Labusch.[14] It was reported that the SSH of Fe3Al by vanadium depends mostly on the elastic modulus misfit, and the atom size misfit plays a minor role. In this work, we first describe the SSH of Fe3Al by Ti, Cr, V, and Mo solutes. This is followed by the study of the combined effect of two solutes in Fe3Al.
II.
EXPERIMENTAL
Iron aluminide alloys were produced by vacuum induction melting. The cooling took place under argon. Samples were prepared from the alloys by electrical discharge machining (EDM). The compressive yield stress was evaluated using a digitally controlled testing machine (INSTRON 1186R). Parallelepipeds with dimensions of 6 9 6 9 10 mm3 were cut by EDM. The deformation rate was 8 9 105 s1. The temperature of 1073 K (800 C) was chosen because this temperature is well above the yield strength anomaly, which is an unusual increase of the strength with increasing temperature, typically observed for Fe-Albased alloys with the maximum in the 773 to 873 K (500 to 600 C) range.[15] Additionally, 1073 K (800 C) is high enough for the vacancy concentration to be in thermal equilibrium. This is noteworthy because at lower temperatures the strength of Fe-Al-based alloys is markedly influenced by quenched-in thermal vacancies,[16] i.e., the strength depends on the processing of the alloys. The investigated alloys are B2-ordered at 1073 K (800 C)
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