Uniaxial tensile plastic deformation and grain growth of bulk nanocrystalline alloys

The uniaxial tensile behavior of as-deposited bulk nanocrystalline (nc) Ni–Fe (average grain size d ≈ 23 nm) and Co–P (d ≈ 12 nm) alloys was investigated. Both alloys have a high strength of about 2 GPa. The nc Ni–Fe alloy exhibits a tensile elongation to failure, εf, in the range 4–7%, depending on the applied strain rate, ε˙. In contrast, the nc Co–P alloy shows rather constant εf of about 2.2%, which is insensitive to ε˙. Tensile plastic deformation causes a grain growth in both alloys. An abnormal grain growth was noticed in the nc Ni–Fe alloy, leading to a bimodal microstructure with large grain sizes up to about 250 nm. While deformation twinning and dislocation motion still play roles, our experimental results indicate that the plastic deformation of the nc alloys is influenced by the grain boundary activities.