Temperature dependence of effective stress in severely deformed ultralow-carbon steel

Masaki Tanaka,Kenji Higashida

doi:10.1080/14786435.2016.1183828

Masaki Tanaka, Kenji Higashida

Open Access

https://doi.org/10.1080/14786435.2016.1183828

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Journal: Philosophical Magazine	Publication Date: Jun 2, 2016
Citations: 10	License type: open-access

Affiliation: Kyushu University

Abstract

The effects of severe plastic deformation on the thermal activation of dislocation gliding in ultralow-carbon steel at low temperatures were investigated. This was done by measuring the temperature dependences of the effective stress, activation volume and activation energy. It was found that the values of all these parameters were lower than those for coarse-grained specimens at low temperatures. In coarse-grained materials, the activation energy should increase with a decrease in the effective stress. This phenomenon, which seemed counterintuitive initially, could be physically interpreted on the basis of the fluctuation in the athermal stress.

Highlights

Materials subjected to severe plastic deformation (SPD) show outstanding mechanical properties such as high strength and toughness [1,2,3,4,5,6,7], in contrast to coarse-grained materials
In order to explain the inverse temperature dependence of the activation volume in severely deformed Cu, Kato et al assumed that the thermally activated process, in SPDed, Cu is the depinning of the dislocations from the grain boundaries introduced in large numbers by the grain refinement caused by the SPD
They calculated the temperature dependence of the activation volume based on their model and demonstrated that the activation volume decreases with the temperature by assuming that one side of the pinned dislocations at the grain boundaries is depinned during the thermally activated process

Summary

Introduction

Materials subjected to severe plastic deformation (SPD) show outstanding mechanical properties such as high strength and toughness [1,2,3,4,5,6,7], in contrast to coarse-grained materials. The effects of SPD on the activation process in bcc metals at low temperatures are expected to be different from those in coarse-grained bcc metals or fcc metals, because the dominant stress component for dislocation gliding is the Peierls (or double-kink nucleation) stress, and the athermal stress necessary for overcoming the long-range stress caused by the high-density dislocations introduced by the SPD process. In these materials, dislocation gliding is the motion in the coexistence of high short-range and long-range barriers. The effects on the thermal activation of the dislocations introduced by the SPD process are discussed

Experimental procedure

Results

Decreases in activation energy and activation volume

Findings

Conclusions