Dissociated dislocation-mediated carbon transport and diffusion in austenitic iron

Ruiwen Xie,Song Lu,Wei Li,Yanzhong Tian,Levente Vitos

doi:10.1016/j.actamat.2020.03.042

Abstract

Dislocation-solute interaction plays fundamental roles in mechanical properties of alloys. Here, we disclose the essential features of dislocation-carbon interaction in austenitic Fe at the atomistic scale. We show that passage of a Shockley partial dislocation in face-centered cubic iron is able to move carbon atoms on the slip plane forward by one Burgers vector, revealing a novel dissociated dislocation-mediated transport mechanism. This mechanism is induced by shear, which is distinct from the normal thermally activated diffusion process. Furthermore, we show that there exists a fast diffusion channel with significantly reduced diffusion energy barrier in the partial dislocation core, which is highly localized and directional. These inherent geometrical features are crucial for understanding the dependence of the diffusivity of dislocation pipe diffusion on the character of dislocations; most importantly, they can result in unbalanced pinning effect on the leading and trailing partials in a mixed dislocation, consequently facilitating stacking fault formation and deformation twinning. This explains the controversial effects of carbon on deformation twinning observed in various alloys. Our findings pave the road to tune mechanical properties of materials by manipulating dislocation-interstitial interaction.

Highlights

Carbon is undoubtedly one of the most important alloying elements in metallurgy, especially in steels
It is well accepted that C is a strong austenite stabilizer and noticeably increases the stacking fault energy (SFE) [1], C addition should suppress deformation twinning (DT) in austenite according to the classical plasticity theory [2]
We studied the interaction mechanisms between partial dislocations and interstitial C atoms in g-Fe and FeÀMn steels at the atomistic scale

Summary

Introduction

Carbon is undoubtedly one of the most important alloying elements in metallurgy, especially in steels. Using quantum-mechanical ab initio calculations, we explore the migration behaviors of C in bulk, SF and partial dislocation core in the double-layer antiferromagnetic (AFMD) g-Fe [25] with a focus of understanding the influence of C on dislocation mobility in high-Mn steels which have Neel temperatures at around room temperature [26,27]. The above findings are crucial for understanding the observed C effects on dislocation planar slip, DSA, DT and MT in a consistent picture, which are beyond the thermodynamic role played by C. diffusion barriers (see Appendix A, Table A.1), as well as C solution enthalpy [32] and SFE [33]. The forces on atoms are converged to less than 0.02 eV A À1 when atomic relaxation is allowed

Computational methodology

Migration energy surface

Dissociated dislocation-mediated transport of C

Fast diffusion channel

Unbalanced pinning

Conclusions