Strain hardening and softening in a nanocrystalline Ni-Fe alloy induced by severe plastic deformation

► Structure-hardness relationship of a nc Ni-Fe alloy processed by HPT was studied. ► Strain hardening, softening and hardening again occurred progressively. ► The hardness evolution is primarily controlled by dislocation density evolution. ► Grain growth and de-twinning played minor roles on the hardness evolution.