Microstructure Evolution during Cold Rolling in a Nanocrystalline Ni-Fe Alloy Determined by Synchrotron X-ray Diffraction

Abstract

Stress softening after cold rolling is observed in an electrodeposited nanocrystalline Ni-Fe alloy. The grain-size distribution becomes much broader after the cold rolling. Microstructure changes, though moderate, such as simultaneously decreased dislocation and twin densities with grain growth during cold rolling, are systematically proved by synchrotron high-energy X-ray diffraction, and transmission-electron microscopy and differential-scanning calorimetry (DSC). The amorphous fractions in the form of grain boundaries are evidenced by the diffuse-background scatterings and large DSC values. Partial dislocation separation calculation, a dislocation mean free path and annihilation model, and texture development together reveal that the current nanocrystalline Ni-Fe alloy exhibits the combined behavior of perfect dislocation slip and grain-boundary mediated deformation.