Quantification of the microstructures of high purity nickel subjected to dynamic plastic deformation

A quantitative microstructural analysis is presented for pure polycrystalline nickel processed by means of dynamic plastic deformation at high strain rates (10(2)-10(3) s(-1)) to strains from 0.3 to 2.9. This analysis covers a number of structural parameters, such as the spacing between and the misorientation angle across dislocation boundaries and high angle boundaries. These boundaries subdivide the structure on a finer and finer scale towards saturation at the highest strain. The structural evolution follows a hierarchical pattern from the formation of cells and cell blocks to a characteristic lamellar structure, which is similar to that observed in metals deformed at a low strain rate by conventional deformation processes. However, at a constant strain the increase in strain rate increases the dislocation density and reduces the distance between deformation-induced dislocation boundaries and high angle boundaries. Shear bands and twins have not been observed. In order to underpin the structural analysis, the mechanical properties as a function of strain have been determined by tensile and hardness tests. The flow stress is 850 MPa, showing that high strain rate deformation has potential as a method to produce strong nanostructured metals by imposing only a moderate strain. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.