Some aspects of the dislocation microstructures in fatigued FeCrAl alloys

Fe25Cr4Al and Fe25Cr2Al (wt.%) alloys were cyclically deformed in air at various total strain amplitudes. Four different structures were observed, in order of decreasing strain: ordinary dislocation cell structures in both alloys at about 1% total strain and above; and “maze” or “labyrinth” structures at intermediate strains, again for both alloys; however, at the lowest strain rates, a typical loop patch structure was found in the 2% aluminium alloy but a precursor to the maze (labyrinth) structure was found in the 4% alloy. That precursor structure seems to be the same as that observed by Mori et al. It would thus appear that the difference between the two alloys lies in the bypassing of the loop-patch structure in the 4% alloy, with, instead, direct construction of dipolar or multipolar walls. Thus the softening observed in the 2% alloy is due to the formation of the loop patches.