High Purity Ultrafine-Grained Nickel Processed by Dynamic Plastic Deformation: Microstructure and Mechanical Properties

Bulk ultrafine-grained samples are processed by dynamic plastic deformation at an average strain rate of 3.3x10(2)s(-1) from bulk coarse-grained nickel with purity higher than 98.4 wt.%. The obtained microstructure is investigated by electron backscattering diffraction, transmission electron microscopy and X-ray line profile analysis. After dynamic deformation the microstructure evolves into submicron-size lamellar and subgrain structures. Evaluation of average grain size shows a heterogeneous microstructure along both the diameter and the thickness of the sample. X-ray line profile analysis reveals high dislocation density of about 13 +/- 2x10(14)m(-2) in the impacted material. The mechanical properties are investigated by means of uniaxial quasi-static compression tests conducted at room temperature. The stress-strain behavior of the impacted Ni depends on the location in the impacted disk and on the orientation of the compression axis relative to the impact direction.