Ab Initio Study of Elastic Properties in Fe 3 Al-based Alloys
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1128-U02-04
Ab Initio Study of Elastic Properties in Fe3Al-based Alloys Martin Friák, Johannes Deges, Frank Stein, Martin Palm, Georg Frommeyer, and Jörg Neugebauer Max-Planck-Institut für Eisenforschung GmbH, Max-Planck Str. 1, D-40237, Düsseldorf, Germany ABSTRACT Fe3Al-based alloys constitute a very promising class of intermetallics with great potential for substituting austenitic- and martensitic steels at elevated temperatures. A wider use of these materials is partly hampered by their moderate ductility at ambient temperatures. Theoretical ab initio based calculations are becoming increasingly useful to materials scientists interested in designing new alloys. Such calculations are nowadays able to accurately predict basic material properties by needing only the atomic composition of the material. We have therefore employed this approach to explore (i) the relation between chemical composition and elastic constants, as well as (ii) the effect transition-metal substituents (Ti, W, V, Cr, Si) have on this relation. Using a scale-bridging approach we model the integral elastic response of Fe3Al-based polycrystals employing a combination of (i) single crystal elastic stiffness data determined by parameter-free first-principles calculations in combination with (ii) Hershey’s homogenization model. The ab initio calculations employ density-functional theory (DFT) and the generalized gradient approximation (GGA). The thus determined elastic constants have been used to calculate the ratio between the bulk B and shear G moduli as an indication of brittle/ductile behavior. Based on this approach we have explored chemical trends in order to tailor mechanical properties. Using this information we have cast a selected set of Fe3Al-based ternary alloys, obtained for these the elastic constants by performing impulse excitation measurements at room as well as liquid nitrogen temperature and compared them with our theoretical results. INTRODUCTION The development of new lightweight materials is crucial for numerous energy-conversion applications in the automotive and aerospace industries. Low-cost and low-density materials operating at higher temperatures ensure a lower fuel consumption and environmentally cleaner and more efficiently produced electricity. Two basic options in materials design and/or functional optimization are the selection of an appropriate chemical composition and the processing of an optimized microstructure. Both characteristics are mutually interlinked and inherently multiscale in nature what make them challenging to study. We address these fundamental aspects to a promising class of lightweight intermetallics: Fe3Al-based alloys exhibiting an excellent high temperature oxidation and sulfidation resistance up to 1000 °C. Therefore, they possess a high potential as a low cost alternative to conventional ferritic, martensitic or austenitic steels [1]. Depending on the Al content Fe-Al alloys exhibit a disordered bcc-state, an ordered B2- or a D03-ordered superlattice structure. Most investigations deal with
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