A three-dimensional mechanistic study of the drivers of classical twin nucleation and variant selection in Mg alloys: A mesoscale modelling and experimental study

• Published in: International journal of plasticity 2021-08, Vol.143, p.103027, Article 103027
• Main Authors: Paramatmuni, Chaitanya, Guo, Yi, Withers, Philip J., Dunne, Fionn P.E.
• Format: Article
• Language: English
• Subjects: Crystal plasticity finite element method; Deformation twinning; Flux density; Internal energy; Magnesium base alloys; Nucleation; Shear stress; Stored energy density; Strain; Twin nucleation site; Twin resolved shear stress; Twinning; Two dimensional analysis
• ISSN: 0749-6419; 1879-2154
• DOI: 10.1016/j.ijplas.2021.103027

This work presents a detailed investigation of twin inception to identify site of twinning, variant type selected, and the strain to nucleate it within a full 3D reconstructed microstructure obtained using 3D-EBSD. Microstructurally-faithful 3D crystal plasticity analysis provides quantitative insight to show that stored energy density is a key factor (rather than stress or other criteria) which identifies the experimentally observed twin nucleation site (which supersedes twin inception), and the strain necessary to drive nucleation. 3D (as opposed to 2D surface) analysis has been shown to be essential. The critical energy density for twin nucleation was found to be ∼0.015 Jm-2 in Mg alloy AZ31. Further, at the predicted nucleation site, the experimentally observed twin variant is shown to be driven by the local twin resolved shear stress. [Display omitted] •The drivers for the nucleation of classical twins in Mg alloy AZ31 are studied in detail using integrated experiments and modelling approach.•The 3D deformed microstructure is obtained by performing serial sectioning of deformed small-scale pillar.•A grain and twin of interest are identified to study the drivers of twin nucleation in 3D.•It is shown that the stored energy density precisely locates the classical twin nucleation sites indicating that they are also driven by local dislocation structures.•The variant selection in classical twins is driven by local twin resolved shear stress.