, Volume 48, Issue 21, pp 7435-7445
Date: 20 Jul 2013

Microstructure and mechanical properties of two-phase Fe30 Ni20 Mn20 Al30 . Part I: Microstructure

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The microstructure of Fe30Ni20Mn20Al30 in both the as-cast condition and after annealing at 823 K for various times up to 72 h was characterized using transmission electron microscopy, scanning transmission electron microscopy, synchrotron-based X-ray diffraction, and atom probe tomography. The microstructure exhibited a basketweave morphology of (Mn, Fe)-rich B2-ordered (ordered b.c.c.) and (Ni, Al)-rich L21-ordered (Heusler type) phases with a lattice misfit of only 0.85 % and interfaces aligned along 〈100〉. The phase width increased from 5 nm for the as-cast alloy to 25 nm for 72 h annealed material, with no change in the elemental partitioning between the phases, with a time exponent for the coarsening kinetics of 0.19. Surprisingly, it was found that the room temperature hardness was largely independent of the phase width.