Grain boundaries in ultrafine grained materials processed by severe plastic deformation and related phenomena

► UFG materials produced by SPD do exhibit specific GBs defined earlier as “non-equilibrium GB”. ► Such boundaries differ from regular GBs on atomic structure and appearance of long-range stresses. ► The apparent thickness of “non-equilibrium” GB is typically in a range of 1 to 2 nm. ► GBs in SPD materials may promote segregations and mechanical mixing that affect the properties. ► “Non-equilibrium” GBs do significantly enhance the atomic mobility in SPD materials.