Modelling of recrystallisation in mechanically alloyed materials

The exceptionally high recrystallisation temperatures of ultra-fine-grained mechanically alloyed metals cannot be adequately explained in terms of γ′ dissolution, dispersoid coarsening, or ordinary grain growth theory. Such alloys have an unusually fine grain structure before recrystallisation, the grain size typically being a fraction of a micrometre. It is demonstrated here that in these circumstances, the fine grains cannot be treated as being topologically independent, because the grain-boundary junctions behave like strong pinning points, preventing the easy nucleation of recrystallisation. A model based on this idea, together with new and published experimental data, are found to explain all of the known features of recrystallisation in mechanically alloyed oxide dispersion strengthened metals.