Shock-Induced Phase Transition and Spallation in Pure Iron under Magnetically Driven Flyer Plate Loading

The magnetically driven device CQ-4 was used to drive a copper flyer plate to impact a pure iron specimen to achieve one dimensional plane-wave loading, and a high-accurate Doppler pin system was utilized to record the free-surface velocity histories of the flyer and specimen.The results indicate that if the pure iron material experiences α ↔ε phase transition during shock loading and unloading, its spallation strength reaches to 3.4 GPa which is distinctly higher than the reported value of 1.2-1.9 GPa without phase transition.The possible cause of this phenomenon is that a multitude of dislocations in the crystal lattices of the pure iron are formed during the α ↔ε reversible phase transition.Moreover, the free-surface velocity history reveals that the spallation has occurred in the near-surface of the specimen.The formation of the shallow spallation may be related to the rarefaction wave formed at the time of reversal phase transition in the pure iron specimen.Because if only consider the interactions between the rarefaction waves generated by the reflection of plastic wave as well as phase transition wave and rarefaction wave when analyzing the stress wave propagations in the flyer-specimen system, it is impossible to interpret the detected shallow spallation in the experiment.