Amorphization of covalently bonded solids under dynamic compression*

In this investigation, we show pulsed laser-driven, shock-induced amorphization in four different covalently bonded solids, namely, silicon, germanium, boron carbide and silicon carbide. The critical threshold for the amorphization scales with the hardness of these materials, yielding B$_{\mathrm{4}}$C\textgreater SiC\textgreater Si\textgreater Ge. Post shock microstructural characterization was conducted to study the deformation/failure mechanism of these materials. The directional feature of the amorphous band suggests that shear stress play a crucial role triggering the crystalline-to-amorphous transition. Shear manifests itself in three possible ways: (1) it causes massive inelastic lattice displacement that can lead to the loss of long-range order; (2) it lowers the melting temperature of; (3) it causes localized heating which lead to localized thermal softening. Nanobeam electron diffraction provides an unprecedented spatial resolution to study the detailed microstructure of the shock-induced amorphous materials. The interfacial strain between the crystalline-amorphous interface will be discussed.