Experimental parameters influencing grain refinement and microstructural evolution during high-pressure torsion

Pure nickel was selected for a detailed investigation of the experimental parameters influencing grain refinement and microstructural evolution during processing by high-pressure torsion (HPT). Samples were examined after HPT using microhardness measurements, transmission electron microscopy and orientation imaging microscopy. Processing by HPT produces a grain size of similar to170 nm in pure Ni, and homogeneous and equiaxed microstructures are attained throughout the samples when they are subjected to at least similar to5 whole revolutions under applied pressures of at least similar to6 GPa. For these conditions, the distributions of grain boundary misorientations are similar in the center and at the periphery of the samples. A simple model is proposed to explain the development of a homogeneous microstructure in HPT. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.