Femtosecond Visualization of hcp-Iron Strength and Plasticity under Shock Compression

Iron is a key constituent of planets and an important technological material. Here, we combine in situ ultrafast x-ray diffraction with laser-induced shock compression experiments on Fe up to 187(10) GPa and 4070(285) K at 108 s-1 in strain rate to study the plasticity of hexagonal-close-packed (hcp)-Fe under extreme loading states. {101 over bar 2} deformation twinning controls the polycrystalline Fe microstructures and occurs within 1 ns, highlighting the fundamental role of twinning in hcp polycrystals deformation at high strain rates. The measured deviatoric stress initially increases to a significant elastic overshoot before the onset of flow, attributed to a slower defect nucleation and mobility. The initial yield strength of materials deformed at high strain rates is thus several times larger than their longer-term flow strength. These observations illustrate how time-resolved ultrafast studies can reveal distinctive plastic behavior in materials under extreme environments.

Automated summary

Through ultrafast experiments, the plasticity behavior of hexagonal-close-packed iron under extreme loading states was studied. The results show that {101 over bar 2} deformation twinning controls the microstructures of polycrystalline iron at high strain rates and occurs within 1 ns.