Microstructure-inferred transition paths in shocked iron single crystals

Single crystal iron samples are laser shocked at two different strain rates using either direct ablation or a time-modulated pulse and an ablator; the samples' cross-section are mapped using electron backscatter diffraction. The post-shock microstructure morphology shows a strong dependence on crystal orientation while the size of reverted grains depends on the loading. Study of the grains' orientation alone is found not to be sufficient to deduce their transformation history, and is augmented with Hadamard compatibility planes and an extended definition of the Schmid factor. A large fraction of grains is explained by α-Fe twinning and little plastic activity is observed close to those grains, indicating a possible substitution of plasticity by twinning. Grains attributed to an α-ε-α cycle are found to form either in the bulk of ε-Fe grains or possibly at the interface between two ε-Fe lamellae.