Statistical mechanics of kinks on a gliding screw dislocation

Max Boleininger,Thomas D Swinburne,Danny Perez,Martin Gallauer,Daniel R Mason,Sergei L Dudarev

doi:10.1103/physrevresearch.2.043254

Abstract

The ability of a body-centered cubic metal to deform plastically is limited by the thermally activated glide motion of screw dislocations, which are line defects with a mobility exhibiting complex dependence on temperature, stress, and dislocation segment length. We derive an analytical expression for the velocity of dislocation glide, based on a statistical mechanics argument, and identify an apparent phase transition marked by a critical temperature above which the activation energy for glide effectively halves, changing from the formation energy of a double kink to that of a single kink. The analysis is in quantitative agreement with direct kinetic Monte Carlo simulations.

Highlights

The rate of plastic deformation of a body-centered-cubic metal depends strongly on temperature, with pure iron notoriously becoming brittle below freezing [1]
The model accounts for formation energies and rates of fundamental reactions involving kinks, which are accessible to atomistic simulations [10,46,47,48], and as such is generally transferable across bcc metals
We show that the activation energy for dislocation glide is halved at high temperature, as the system crosses into the thermodynamic limit

Summary

INTRODUCTION

The rate of plastic deformation of a body-centered-cubic (bcc) metal depends strongly on temperature, with pure iron notoriously becoming brittle below freezing [1]. Despite the extensive use of screw dislocation mobility laws in coarsegrained methods for modeling plastic deformation [17,18,19,20], there is still no suitable analytical expression able to capture the full complexity of dislocation mobility, consistent with the microscopic statistical mechanics description of a fluctuating dislocation line, including the crossover in activation energy noted above. In this contribution, we give a closed-form expression for the glide velocity of a screw dislocation in the kink-limited regime as a function of temperature, resolved shear stress, and. Using the average formation energy is not an approximation because kinks are only formed in pairs, provided periodic boundary conditions apply

EQUILIBRIUM PROPERTIES

NONEQUILIBRIUM STEADY STATE

COMPARISON TO KMC

50 MPa 100 MPa 150 MPa

Findings

CONCLUSION