Abstract
Iron is a key constituent of planets and an important technological material. Here, we combine insitu ultrafast x-ray diffraction with laser-induced shock compression experiments on Fe up to 187(10)GPa and 4070(285)K at 10^{8} s^{-1} in strain rate to study the plasticity of hexagonal-close-packed (hcp)-Fe under extreme loading states. {101[over ¯]2} deformation twinning controls the polycrystalline Fe microstructures and occurs within 1ns, 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.
Highlights
Iron is a key constituent of planets and an important technological material
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-Fe under extreme loading states. f101 ̄2g 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
We build upon a novel experimental layout and use in situ x-ray diffraction to measure polycrystalline texture and deviatoric stress in situ up to pressure and hightemperature (P-T) conditions of 199 GPa and 4383 K at a strain rate on the order of 108 s−1
Summary
Femtosecond Visualization of hcp-Iron Strength and Plasticity under Shock Compression. Our experiment allows measurements of stress and texture at the nanosecond timescale, as a shock progresses into the sample, and identification of the time dependence of plastic flow This information is critical to feed constitutive models of materials under extreme strain rates, which, until now, have only been available using sequences of multiscale calculations [4,6]. We observe a fast increase of elastic stresses prior to plastic yielding, observed in two experiments This initial elastic overshoot is a distinctive feature of plastic deformation at high strain rates for which a peak elastic precursor is reached before generating a sufficient defect density for the onset of plastic flow
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