Abstract
Plastic deformation of polycrystalline materials under shock wave loading is a critical characteristic in material science and engineering. However, owing to the nanosecond time scale of the shock-induced deformation process, we currently have a poor mechanistic understanding of the structural changes from atomic scale to mesoscale. Here, we observed the dynamic grain refinement of polycrystalline aluminum foil under laser-driven shock wave loading using time-resolved X-ray diffraction. Diffraction spots on the Debye-Scherrer ring from micrometer-sized aluminum grains appeared and disappeared irregularly, and were shifted and broadened as a result of laser-induced shock wave loading. Behind the front of shock wave, large grains in aluminum foil were deformed, and subsequently exhibited grain rotation and a reduction in size. The width distribution of the diffraction spots broadened because of shock-induced grain refinement and microstrain in each grain. We performed quantitative analysis of the inhomogeneous lattice strain and grain size in the shocked polycrysalline aluminum using the Williamson-Hall method and determined the dislocation density under shock wave loading.
Highlights
Microstructural deformation, and grain refinement and rotation in polycrystalline metal materials under shock compression are important characteristics, which determine material properties, such as strength and elastic-plastic deformation
The number of broadened peaks increased as the shock wave propagated through the polycrystalline aluminum foil
We counted approximately 1300 individual diffraction spots on each Debye-Scherrer ring at Ghkl, which were acquired from 25 different diffraction images before and under shock compression
Summary
Microstructural deformation, and grain refinement and rotation in polycrystalline metal materials (for example, engineering alloys and ceramics) under shock compression are important characteristics, which determine material properties, such as strength and elastic-plastic deformation. The application of stroboscopic time-resolved X-ray diffraction using the intense, broadband X-ray pulses enables in situ characterization of plastic deformation in shock-compressed polycrystalline materials. Because of the broad bandwidth energy (ΔE/E = 1.45%) of the X-ray pulse, we were able to observe the dynamic process of grain refinement and fragmentation in the shock-compressed materials from the X-ray diffraction patterns. We observed the evolution and arrangement of diffraction spots on Debye-Scherrer rings in situ These features derive from individual crystallites and enabled us to determine the in situ dislocation density
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