Elastoplastic and polymorphic transformations of iron at ultra-high strain rates in laser-driven shock waves

Abstract

Elastoplastic and polymorphic α–ε transformations in iron films induced by ultra-short laser-driven shock waves are studied. Interpretation of time-resolved interferometric measurements is performed using an inverse analysis technique of experimental rear-side velocity profiles. The lasts are obtained by numerical differentiation of free surface displacements detected by probe laser pulses. The inverse analysis techniques are validated in consistent two-temperature hydrodynamics and molecular dynamics simulations of laser energy deposition and diffusion, generation, and propagation of shock waves in a polycrystalline iron sample. The stress–strain diagrams containing information about elastoplastic deformation and phase transformation are reconstructed by the inverse analysis. We found that the polymorphic transformation in iron under picosecond duration of loading requires much higher stress in contrast to that in microsecond-scale plate-impact experiments. Moreover, such transition may be accomplished partially even at very high stresses if an unloading tail after the shock front is too short.