Slip-free multiplication and complexity of dislocation networks in FCC metals

Sh Akhondzadeh,Ryan B Sills,Nicolas Bertin,Wei Cai

doi:10.1186/s41313-020-00024-y

Abstract

During plastic deformation of crystalline solids, intricate networks of dislocation lines form and evolve. To capture dislocation density evolution, prominent theories of crystal plasticity assume that 1) multiplication is driven by slip in active slip systems and 2) pair-wise slip system interactions dominate network evolution. In this work, we analyze a massive database of over 100 discrete dislocation dynamics simulations (with cross-slip suppressed), and our findings bring both of these assumptions into question. We demonstrate that dislocation multiplication is commonly observed on slip systems with no applied stress and no plastic strain rate, a phenomenon we refer to as slip-free multiplication. We show that while the formation of glissile junctions provides one mechanism for slip-free multiplication, additional mechanisms which account for the influence of coplanar interactions are needed to fully explain the observations. Unlike glissile junction formation which results from a binary reaction between a pair of slip systems, these new multiplication mechanisms require higher order reactions that lead to complex network configurations. While these complex configurations have not been given much attention previously, they account for about 50% of the line intersections in our database.

Highlights

A fundamental goal in dislocation theory and physical metallurgy is to understand how and why dislocations multiply
Glissile+coplanar multiplication mechanism We propose that the majority of A2 links for the [ 4 9 10] loading orientation are created by reactions between coplanar slip systems, i.e., A3 + A6 = A2, as opposed to glissile reactions A3 + D6 = A2 and A6 + C3 = A2
We observed that while the plastic strain rates γi on slip systems are generally not correlated with one another, dislocation densities ρi on coplanar slip systems are correlated

Summary

Introduction

A fundamental goal in dislocation theory and physical metallurgy is to understand how and why dislocations multiply. Such multiplication affects numerous mechanical properties of crystalline solids, such as the strain hardening rate, fracture toughness, fatigue-life, and creep-life, to name a few. Theories which predict the multiplication rate on the basis of fundamental dislocation processes have been elusive; existing models for dislocation multiplication are either phenomenological (i.e., not connected to the underlying physical mechanisms) (Mecking and Kocks 1981; Roters et al 2010) or derived on the basis of assumed multiplication mechanisms, such as storage via junction formation (Devincre et al 2008; Kubin et al 2008a). The goal of this work is to elucidate these discoveries and discuss their importance and implications

Objectives

Findings

Discussion

Conclusion