Dynamic evolution of microstructure during laser shock loading and spall failure of single crystal Al at the atomic scales

A hybrid atomistic-continuum method comprising molecular dynamics combined with a two-temperature model (MD-TTM) is used to investigate the ultra-fast laser shock compression and spallation behavior of pure Al films. The laser material interaction, as predicted using MD-TTM models, suggests laser melting followed by the creation of a compressive shock wave that travels through the metal followed by wave reflections and interactions to initiate spallation failure. MD-TTM simulations investigate the influence of laser parameters by varying the laser fluence values from 0.5 to 13 kJ/m² and a duration of 150 fs for the [001] orientation. The microstructural response during the various stages that lead to dynamic failure of single crystal Al is studied by characterizing the temporal evolution of the solid-liquid interface, shock wave structure, defect evolution (dislocations and stacking faults), as well as void nucleation and spall failure. The hybrid method is also used to investigate the microstructure evolution during compression and spall failure for the [110] and [111] orientations for the same laser loading conditions. The variations in the spall strengths observed for the variations in strain rates and shock pressures generated suggest that the evolution of microstructure plays an important role in determining the spall strength of the metal. The analysis of defect structures generated suggests that the spall strength is determined by the density of stair-rod partials in the microstructure simulations with the highest spall strength corresponding to the lowest number of stair-rod partials in the metal.