Authors: A Vorhauer R Pippan
Publish Date: 2007/12/20
Volume: 39, Issue: 2, Pages: 417-429
Abstract
Armco Iron was severely deformed by means of a highperformance highpressure torsion HPT tool at a hydrostatic pressure of 54 GPa at low homologous temperatures T m between 008 and 040 T m The flow stress was estimated from the measured torque during severe plastic deformation SPD At all investigated deformation conditions a saturation in the flow stress at large strains without any decline was obtained It is shown that this occurrence of a “steady state” at low homologous temperatures is significantly influenced by the deformation parameters whereby an increase in deformation temperature or a decrease in strain rate results in a decrease in onset strain and an increase in flow stress in both the steady state and the size and aspect ratio of the structural elements The Zener–Hollomon parameter is used to analyze the mechanical and microstructural properties as a function of the processing parameters this shows that the investigated range of deformation conditions is divided into two regimes For comparable highdeformation temperatures the occurrence of a steady state is ascribed to a process similar to geometric dynamic recrystallization DRX Possible reasons for the occurrence of a different behavior in the low homologous temperature regime are discussed the size of the crystallites formed during straining by the subdivision of the initial grains is considered to play an important roleComparison of the fraction of corrected and uncorrected steadystate flow stress obtained from insitu torque measurements during HPT under the assumptions of sliding of the material that forms the burr against one anvil dashed lines and deformation of the burr material solid line respectively See text for further description26
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