Relative grain boundary energies in ultrafine grain Ni obtained by high pressure torsion

We employed the thermal grooving method and determined the ratio of grain boundary and surface energies in ultrafine grain Ni produced by high pressure torsion. The average values of the relative grain boundary energies were 0.41 and 0.35 after the primary recrystallization at 500°C, and after equilibrating annealing at 800°C, respectively. A significant decrease of the energy of individual stationary grain boundaries is found after two consecutive heat treatments at 500 and 600°C. We discussed the obtained results in terms of an interplay of relaxation and consumption of deformation-induced defects by the grain boundaries.