Strain softening in nanocrystalline Ni–Fe alloy induced by large HPT revolutions

The influence of strain on the hardness of an electrochemically deposited nanocrystalline Ni–20 wt.% Fe alloy processed by high-pressure torsion (HPT) for 20 and 30 revolutions was investigated. Strain softening followed by a stable hardness value was observed. Structural investigations revealed that, while dislocation density was important, continuous grain growth played a major role in the strain softening. The stable hardness indicates that an equilibrium structure was achieved, supporting a dynamic balance between deformation-induced grain growth and grain refinement and between deformation-induced dislocation generation and dislocation annihilation.

► A nanocrystalline Ni–Fe alloy was processed by HPT to 20 and 30 revolutions.
► A strain softening stage and a stable hardness stage were observed.
► The strain softening is due to grain growth and dislocation density reduction.
► The stable hardness indicates that an equilibrium structure was achieved.