Rare twin linked to high-pressure phase transition in iron

At approximately 13 GPa, body-centered cubic alpha-iron undergoes a fully reversible, pressure-induced phase transition into hexagonal close-packed epsilon-iron. Microstructural evidence of this phase transition has been identified in the fully reverted alpha-iron as a large number of {3 3 2}〈113〉 twins found primarily as secondary twins within {1 1 2}〈111〉 primary twins. The {3 3 2}〈113〉 twins were produced during high-pressure shock-loading of 1018 steel at a peak pressure above the alpha-epsilon phase transition pressure. The twins were identified using electron backscattered diffraction and transmission electron microscopy.