Principles of high-pressure torsion and equal-channel angular pressing: A comparison of microstructural characteristics

Two major procedures are currently in use for the production of ultrafine-grained materials through the imposition of severe plastic deformation: high-pressure torsion (HPT) in which a sample is subjected to a high pressure with concomitant torsional straining and equal-channel angular pressing (ECAP) where a sample is pressed through a die constrained within a channel that is bent through an abrupt angle. In both of these procedures, the samples are subjected to very high strains but there is no reduction in their cross-sectional dimensions. This paper examines the principles of these two processing techniques with special reference to the production of materials having reasonably homogeneous microstructures and the potential for developing an array of ultrafine grains separated by grain boundaries having high angles of misorientation.