Three-dimensional nucleation and growth of deformation twins in magnesium

TL;DR

This paper presents the first 3D in-situ characterization of deformation twinning in magnesium alloys, revealing complex growth behaviors and the role of microstructural features in crack initiation.

Contribution

It introduces a novel 3D in-situ dark-field X-ray microscopy method combined with crystal plasticity modeling to study deformation twins inside grains.

Findings

Triple junctions are key sites for twin nucleation.

Twin growth occurs in multiple directions irregularly.

Dislocation accumulation at twin interfaces can lead to cracks.

Abstract

At two-thirds the weight of aluminum, magnesium alloys have the potential to significantly reduce the fuel consumption of transportation vehicles. These advancements depend on our ability to optimize the desirable versus undesirable effects of deformation twins: three dimensional (3D) microstructural domains that form under mechanical stresses. Previously only characterized using surface or thin-film measurements, here, we present the first 3D in-situ characterization of deformation twinning inside an embedded grain over mesoscopic fields of view using dark-field X-ray microscopy supported by crystal plasticity finite element analysis. The results reveal the important role of triple junctions on twin nucleation, that twin growth behavior is irregular and can occur in several directions simultaneously, and that twin-grain and twin-twin junctions are the sites of localized dislocation accumulation, a necessary precursor to crack initiation.