Real-time x-ray characterization of shock compressed molybdenum single crystals

Body-centered cubic (BCC) refractory metals, and their alloys, play a critical role in many applications including electronics, medical, aerospace, and armor/anti-armor applications due to their high temperature-specific strength, creep resistance, and ductility. In general, the continuum response of materials (including BCC metals) is often influenced by microscopic deformation mechanisms during dynamic-inelastic loading such as dislocation generation, dislocation motion, and deformation twinning. Current constitutive models rely on investigations that involve continuum measurements followed by postmortem microstructural analysis of shock-recovered samples. However, this may not reflect the true material behavior from the immediate processing of the shock wave. Therefore, real-time in-situ atomistic characterization is necessary to link the microstructure to the macroscopic response. In this study, normal plate impact experiments are conducted on single crystal molybdenum oriented along the [100] or [111] direction at pressures ranging from 9-19 GPa. These experiments are coupled with both photonic Doppler velocimetry (PDV) continuum measurements and real-time Laue x-ray diffraction (XRD), at the Dynamic Compression Sector (DCS) at the Advanced Photon Source (APS). Here, the role of crystal orientation on deformation mechanisms is explored during the elastic-plastic regime and the Hugoniot steady-state response. A complementary simulation methodology is developed to analyze the evolution of the Laue diffraction spots captured during impact. Using the lattice strains determined from the shifts of Laue spots, dislocation slip along [110]<111> and [112]<111> is observed to be the probable deformation mechanism during shock compression with negligible anisotropy observed at the Hugoniot state. For the first time, real-time evidence of molybdenum undergoing deformation twinning along [112]<111> is observed during shock release and occurs beyond a critical pressure irrespective of the loading orientation.