Prediction of thermal cross-slip stress in magnesium alloys from direct first principles data

TL;DR

This paper presents a first-principles statistical model predicting how solutes like Sc, K, and Na affect the cross-slip stress in magnesium alloys, enabling improved formability at lower temperatures.

Contribution

It introduces a novel first-principles and statistical approach to model thermally-activated dislocation cross-slip in magnesium alloys with solutes.

Findings

Lowered forming temperatures for Mg-0.7at.%Sc, Mg-0.4at.%K, and Mg-0.6at.%Na by approximately 250°C.

Development of a statistical distribution model for activation energies and energy landscape roughness.

Prediction of solute effects on magnesium alloy formability using direct electronic structure calculations.

Abstract

We develop a first-principles model of thermally-activated cross-slip in magnesium in the presence of a random solute distribution. Electronic structure methods provide data for the interaction of solutes with prismatic dislocation cores and basal dislocation cores. Direct calculations of interaction energies are possible for solutes---K, Na, and Sc---that lower the Mg prismatic stacking fault energy to improve formability. To connect to thermally activated cross-slip, we build a statistical model for the distribution of activation energies for double kink nucleation, barriers for kink migration, and roughness of the energy landscape to be overcome by an athermal stress. These distributions are calculated numerically for a range of concentrations, as well as alternate approximate analytic expressions for the dilute limit. The analytic distributions provide a simplified model for the maximum cross-slip softening for a solute as a function of temperature. The direct interaction calculations predict lowered forming temperatures for Mg-0.7at.%Sc, Mg-0.4at.%K, and Mg-0.6at.%Na of approximately 250C.