Grain boundary mobility in Fe-base oxide dispersion strengthened PM2000 alloy

It has been possible to measure the average interfacial velocities of grain boundaries during the process of recrystallisation of an oxide dispersion-strengthened iron-base alloy manufactured using the mechanical alloying technique. 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 bearing in mind the pinning effect of the non-random distribution of oxide particles. It is concluded that the boundaries have a high mobility. This conclusion adds to the growing evidence that the alloy has great difficulty in nucleating recrystallisation because of the ultrafine and uniform starting-microstructure in which the 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.