Plastic yielding and deformation bursts in the presence of disorder from coherent precipitates

TL;DR

This study uses 3D dislocation dynamics simulations to explore how coherent precipitates influence the collective behavior and yielding transition of dislocations in FCC crystals, revealing a depinning transition at high precipitate densities.

Contribution

It demonstrates how increasing precipitate density and interaction strength induces a true yield transition, advancing understanding of precipitation hardening effects on dislocation dynamics.

Findings

Dislocation jamming dominates in low precipitate scenarios.

A true yield transition occurs at high precipitate density.

Dislocation avalanches exhibit critical scaling near yielding.

Abstract

Alloying metals with other elements is often done to improve the material strength or hardness. A key microscopic mechanism is precipitation hardening, where precipitates impede dislocation motion, but the role of such obstacles in determining the nature of collective dislocation dynamics remains to be understood. Here, three-dimensional discrete dislocation dynamics simulations of FCC single crystals are performed with fully coherent spherical precipitates from zero precipitate density upto $\rho_p = 10^{21}\,\text{m}^{-3}$ and at various dislocation-precipitate interaction strengths. When the dislocation-precipitate interactions do not play a major role the yielding is qualitatively as for pure crystals, i.e., dominated by "dislocation jamming", resulting in glassy dislocation dynamics exhibiting critical features at any stress value. We demonstrate that increasing the precipitate density and/or the dislocation-precipitate interaction strength creates a true yield or dislocation assembly depinning transition, with a critical yield stress. This is clearly visible in the statistics of dislocation avalanches observed when quasistatically ramping up the external stress, and is also manifested in the response of the system to constant applied stresses. The scaling of the yielding with precipitates is discussed in terms of the Bacon-Kocks-Scattergood relation.