Unique atomic structure of metals at the moment of fracture induced by laser shock

Abstract

To effectively control the mechanical properties of structural materials and design their safety margins, understanding the properties of metal fracture is essential. However, it is difficult to experimentally investigate the atomic structures at the moment of fracture; therefore, the detailed fracture mechanism remains an active area of research. In this study, we in situ examined how the atomic structure of copper changes during the fracture process on the nanosecond scale using X-ray absorption spectroscopy and X-ray diffraction. The fracture was triggered by a shock wave induced by an optical laser and was examined with a single 100-ps synchrotron X-ray pulse with a delay time of 0–200 ns. This novel experimental approach provides insights into how the short- and long-range order of an atomic structure change on the nanosecond scale. The results showed that there was an irreversible change in the deformation state on the nanosecond scale. The initial elastic deformation state (0–20 ns) was superseded by a plastic deformation state (20–50 ns). Then, at the moment of fracture (50–320 ns), the plastic deformation state transformed into a state in which the heterogeneous atomic structures exhibited short-range disorder while maintaining long-range order (a “short-range-disorder-only” state). This unique “short-range-disorder-only” state, which has never been reported using conventional ex situ analytical techniques, triggered metal fracture; therefore, controlling the occurrence of this state could suppress fracture and allow the design of reasonable metal safety margins to avoid overengineering.