2008 Volume 94 Issue 12 Pages 582-589
Formation mechanisms of ultrafine grained structures in severe plastic deformation (SPD) of metallic materials are overviewed and discussed on the basis of experimental results. It is concluded that the formation of ultrafine grained structures in SPD can be understood in terms of grain subdivision. The ultrafine grained structures in the as-SPD materials are essentially deformation structures, although they can be simultaneously considered as grain structures from a viewpoint of large misorentation to each other. When the SPD processed materials are annealed, a continuous change in microstructures can happen, which might be called continuous recrystallization. The phenomenon is fundamentally discussed after determining the nucleation events in recrystallization.