Lamellar coarsening in Fe28Ni18Mn33Al21 and its influence on room temperature tensile behavior

As-cast nanostructured eutectoid Fe28Ni18Mn33Al21, which consists of ∼50 nm wide (Ni, Al)-rich B2 and (Fe, Mn)-rich fcc aligned phases, was annealed at 1173 K for various times up to 250 h in order to produce a wide range of phase widths (up to 2.5 μm) over which to evaluate the mechanical properties. The coarsening kinetics over these two orders of magnitude change could be described by r2 − ro2 = kt, where r is the phase width after time t at 1173 K, ro is initial phase width, and k is a constant. The yield strength, σy, was found to follow a Hall-Petch-type relationship, i.e. σy = σo  + kyλ−1/2, where λ is the fcc phase width, σo is the strength of the single-phase material, and ky is a constant. Interestingly, the work-hardening rate also roughly followed a λ−1/2 relationship, while the elongation to failure increased as λ increased from failure before yielding in the as-cast material to ∼7% for the material with the largest λ values.