Microstructural Characteristics of Ultrafine-Grained Nickel

Abstract

A detailed investigation was conducted to evaluate the microstructural characteristics in samples of pure nickel processed using three different procedures of severe plastic deformation (SPD): equal-channel angular pressing (ECAP), high-pressure torsion (HPT) and a combination of ECAP and HPT. Several different experimental techniques were employed to measure the grain size distributions, the textures, the distributions of the misorientation angles and the boundary surface energies in the as-processed materials. It is shown that a combination of ECAP and HPT leads both to a greater refinement in the microstructure and to a smaller fraction of boundaries having low angles of misorientation. The estimated boundary surface energies were higher than anticipated from data for coarse-grained materials and the difference is attributed to the non-equilibrium character of many of the interfaces after SPD processing.

Texture evolution in high-pressure torsion processing

“…The texture of materials with high γ SFE such as pure Al (~160 mJ/m 2 ) [116][117][118]138], Pd-10Au (% wt. )( ~150 mJ/m 2 ) [133] and pure Ni (~128 mJ/m 2 ) [122,[139][140][141] consist of a weak A-fiber and strong B-fiber with the dominance of the C component (as shown in Figure 4a). However, changing the initial grain size of the Pd-10Au alloy leads to a very different deformation texture [133,134] where this effect of the initial grain size is discussed in the next section.…”