Heterogeneous flow during high-pressure torsion

Abstract

High-Pressure Torsion (HPT) has attracted significant attention in recent years as an effective technique to process ultrafine and nanostructured materials. The hydrostatic pressure developed during processing prevents the occurrence of cracks and the low thickness to diameter ratio provides the opportunity for developing high strains at low numbers of rotations. The present work analyses the plastic flow during HPT. Experimental results and computer modeling are used to describe heterogeneous plastic flow. It is shown that variations in structure, hardness and in the distribution of strain are observed along the disc thickness. The sources of these heterogeneities are discussed.

Effect of applied pressure on microstructure development and homogeneity in an aluminium alloy processed by high-pressure torsion

“…The plastic deformation is related to the friction coefficient [18,25,58] which depends upon the anvil roughness [59] and the applied pressure. Thus, a low hydrostatic pressure during HPT processing may promote slipping especially during the first revolution when the sample is usually matching to the anvil.…”

Microstructure and Hardness Evolution in Magnesium Processed by HPT

“…Minor variations in distribution of strain along the sample thickness has been predicted by finite element modelling 40,41 due to friction and variations in hardness distribution have been reported in samples with low diameter to thickness ratio 39,42 . However, experiments have shown significant heterogeneity in hardness distribution along the disc thickness in a magnesium alloy in samples with high diameter to thickness ratio 43,44 . Moreover, it is known that the high amount of defects introduced by plastic deformation leads to the formation of low angle boundaries in the early stage of processing and the misorientation of these boundaries increase with continuing processing.…”