It has been possible to measure directly the interfacial velocities of individual grain boundaries during the process of recrystallization of an oxide dispersion-strengthened iron-base alloy manufactured using the mechanical alloying technique. The alloy has the chemical composition Fe-20Cr-5.5Al-0.5Ti wt% and contains 0.5 wt% of yttrium oxide particles.
The measurements could be made using optical microscopy because the recrystallised grains are orders of magnitude larger than the surrounding unrecrystallised material. Furthermore, the peculiar way in which the alloy recrystallises, made it possible to observe large, flat segments of boundaries as they advanced into the higher energy matrix. The data have been analysed theoretically to show that the boundaries have a high mobility which is not limited by the dispersoids or by any solute drag effect. The work adds to the growing evidence that the alloy has great difficulty in nucleating recrystallization because of the ultrafine starting microstructure in which grain boundary junctions are so closely spaced that they prevent strain-induced grain boundary migration; in other words, the junctions themselves are powerful pinning points.
Movie showing the motion of the recrystallization front. The boundary moves from the top to the bottom of the field of view. The movie is in AVI format.
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