Unconventional Deformation Twinning Mechanisms in Magnesium at High Strain Rates

Ventura, Nicolò Maria della; Sharma, Amit; Jain, Manish; Kalácska, Szilvia; Edwards, Thomas Edward James; Cayron, Cyril; Logé, Roland; Michler, Johann; Maeder, Xavier

SSRN Electronic Journal (2021)

Despite 150 years of research, there is still a lack of experimental evidence on how deformation twinning in hexagonal-close-packed (HCP) metals evolves at different strain rates. Here, we present a systematic investigation of { } extension twinning mechanism in single crystal magnesium micropillars deformed over seven orders 1012 of magnitude of strain rate, from 10-4 to 500 s-1, revealing how the accommodation of newly formed twins depends on the kinetic compatibility of interfacial processes when high deformation rates are imposed. This work shows that deformation twinning is not only stress- but also strongly time-controlled. Away from quasi-static conditions, simple considerations of twinning shear do not suffice to describe unconventional twin morphologies, requiring the competition between dislocations and lattice distortions. Under shock compressions, the basal/prismatic transformation establishing a lattice misorientation of 90° governs the parent?twin conversion. The results illustrated here demonstrate that some of the recent interpretations deduced by particular twin morphologies are not universally valid. This work aims at closing the gap between currently reported modelling and macroscale high strain rate results, broadening the fundamental understanding of twinning in HCP crystals.