Dislocation Networks and the Microstructural Origin of Strain Hardening

TL;DR

This paper investigates how dislocation junction formation influences strain hardening in FCC copper, using discrete dislocation dynamics simulations to reveal the microstructural mechanisms and key junction types involved.

Contribution

It demonstrates that dislocation junction formation, especially glissile junctions, governs strain hardening, with a novel model linking microstructure evolution to hardening rate.

Findings

Dislocation network segments follow an exponential length distribution.

Junction formation rate controls strain hardening rate.

Glissile junctions are the dominant contributors to strain hardening.

Abstract

When metals are plastically deformed, the total density of dislocations increases with strain as the microstructure is continuously refined, leading to the strain hardening behavior. Here we report the fundamental role played by the junction formation process in the connection between dislocation microstructure evolution and the strain hardening rate in face-centered cubic (FCC) Cu, as revealed by discrete dislocation dynamics (DDD) simulations. The dislocation network formed during [001] loading consists of line segments whose lengths closely follow an exponential distribution. This exponential distribution is a consequence of junction formation by dislocations on different slip planes, which can be modeled as a one-dimensional Poisson process. We show that, according to the exponential distribution, the dislocation microstructure evolution is governed by two non-dimensional parameters, and the hardening rate is controlled by the rate of stable junction formation. By selectively disabling specific junction types in DDD simulations, we find that among the four types of junctions in FCC crystals, glissile junctions make the dominant contribution to the strain hardening rate.