Effect of the grain-boundary state and grain size on the mechanisms of creep of submicrocrystalline nickel

The effect of preliminary annealings at temperatures below the recrystalliz ation temperature (T < 573 K) on the microstructure and activation energy o f creep (Q(c)) at T = 423 and 473 K of submicrocrystalline nickel obtained by severe plastic deformation (equal-channel angular pressing) was studied. The substantial change in the magnitude of Q(c) in the samples after such "hyporecrystallization" annealings, in which only the specific grain-bounda ry state changes without changes in grain size, is explained as a consequen ce of various contributions of grain-boundary sliding to the total deformat ion upon creep.