155. non-equilibrium simulations of shock-induced horizontal defects and amorphization in 4h silicon carbide.
Name: Rachel Marie Flanagan
Grad Year: 2020
We perform non-equilibrium molecular dynamics simulations of 4H silicon carbide using a semi-empirical Tersoff potential. There are over 200 polymorphs of silicon carbide, but the hexagonal 4H structure is under explored compared to the cubic 3C structure. Using a controlled piston, we produce a shock wave along the  axis and observe the formation of defects along the basal plane, perpendicular to the shock front. The observed defects are unique to the loading direction and the activation of basal slip in the hexagonal system. These shear-driven defects evolve as the shock wave propagates through the system, leading to directional amorphization. Present results agree with experiments where horizontal stacking faults and amorphization are observed following laser shock compression and recovery. Laser shock-recovery experiments on  oriented 4H silicon carbide were carried out at Jupiter Laser Facility, LLNL. Post-mortem high-resolution transmission electron microscopy revealed that above a certain shock threshold, directional amorphous bands are observed in the vicinity of the shock surface. These amorphous bands are either inclined or horizontal to the direction of shock wave, showing agreement between the simulations and the experiment.
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Aerospace, Defense, Security | Electronics/Photonics | Materials