Non-glide effects and dislocation core fields in BCC metals

Antoine Kraych,François Willaime,Emmanuel Clouet,Lisa Ventelon,Lucile Dezerald,David Rodney

doi:10.1038/s41524-019-0247-3

Abstract

A hallmark of low-temperature plasticity in body-centered cubic (BCC) metals is its departure from Schmid’s law. One aspect is that non-glide stresses, which do not produce any driving force on the dislocations, may affect the yield stress. We show here that this effect is due to a variation of the relaxation volume of the 1/2langle 111rangle screw dislocations during glide. We predict quantitatively non-glide effects by modeling the dislocation core as an Eshelby inclusion, which couples elastically to the applied stress. This model explains the physical origin of the generalized yield criterion classically used to include non-Schmid effects in constitutive models of BCC plasticity. We use first-principles calculations to properly account for dislocation cores and use tungsten as a reference BCC metal. However, the methodology developed here applies to other BCC metals, other energy models and other solids showing non-glide effects.

Highlights

As stated in 1983 by Christian in the title of his seminal review paper,[1] the low-temperature plasticity of body-centered cubic (BCC) metals shows “surprizing features” that, more than 30 years later, are still far from understood
Chief among them is the breakdown of the Schmid law, the fact that contrary to closepacked metals like face-centered cubic (FCC) metals, the plastic yield of BCC metals at low temperatures does not depend only on the resolved shear stress, i.e., the component of the applied stress tensor that produces a shear in the slip plane and along the slip direction
In BCC metals, the yield stress depends on the orientation of the shear plane, resulting in the so-called twinning/ antitwinning (T/AT) asymmetry, and on components of the stress tensor that do not drive plastic deformation, called nonglide stresses. It is well-established that non-Schmid effects are due to the core properties of screw dislocations with a 1=2h111i Burgers vector that are responsible for the low-temperature plastic deformation of BCC metals.[2,3]

Summary

INTRODUCTION

As stated in 1983 by Christian in the title of his seminal review paper,[1] the low-temperature plasticity of body-centered cubic (BCC) metals shows “surprizing features” that, more than 30 years later, are still far from understood. In BCC metals, the yield stress depends on the orientation of the shear plane, resulting in the so-called twinning/ antitwinning (T/AT) asymmetry, and on components of the stress tensor that do not drive plastic deformation, called nonglide stresses It is well-established that non-Schmid effects are due to the core properties of screw dislocations with a 1=2h111i Burgers vector that are responsible for the low-temperature plastic deformation of BCC metals.[2,3] The breakdown of the Schmid law is ubiquitous among BCC metals and has been reported both experimentally[4,5,6,7,8,9] and in atomic-scale computer simulations of screw dislocations.[10,11,12,13,14]. The methodology developed here is general and can be applied to all BCC metals and other solids showing non-glide effects

RESULTS

Kraych et al 4

DISCUSSION