Strong pinning of triple junction migration for robust high strain nanostructures

ABSTRACT

The universality of a key recovery mechanism: triple junction migration in high strain nanostructures is revealed herein. This migration is the only means to uniformly coarsen deformed lamellar microstructures. Migration of medium to high angle geometrically necessary boundaries at triple junctions is resisted by strong pinning phenomena. Pinning by low angle dislocation boundaries is the novel mechanism that greatly adds to the solute drag of these higher angle boundaries during migration at triple junctions. Solutes furthermore cause a significant increase in the dislocation density of the low angle boundaries formed during deformation and thus greatly enhance the observed pinning. Boundary pinning by dislocation boundaries and solute drag is analysed for deformed Ni of different purities via in and ex situ electron microscopy. A kinetic model is utilised to obtain activation energies that quantitatively demonstrate the strength of this pinning. A new strategy for achieving robust nanostructured metals is developed based on solute and dislocation pinning of triple junction migration – a universal recovery mechanism in deformed lamellar microstructures.

KEYWORDS:

• Deformation microstructure
• triple junction migration
• recovery kinetics
• solute drag
• dislocation pinning
• activation energy

Acknowledgements

The authors are grateful to N. Hansen and D. Juul Jensen for valuable comments, and to Y. B. Zhang for providing the deformed 3N Ni samples and his unpublished raw data for the recrystallisation/recovery analyses of 3N Ni performed herein.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Tianbo Yu http://orcid.org/0000-0001-9525-9354

Notes

1. It should be noted that the kinetics of recrystallization for 3N Ni at 220°C shown in Figure 13(c) is slightly different from that reported in a recent recrystallization study of the same deformed Ni [17]. This difference may have its cause in heterogeneities introduced during deformation and therefore a larger experimental error in the estimated activation energy is expected in the 3N Ni compared to that in the 2N Ni.

Additional information

Funding

This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (ERC Advanced grant – M4D/grant agreement number 788567).