|About this Abstract
||2020 TMS Annual Meeting & Exhibition
||Nix Award and Lecture Symposium: Mechanistic Understanding of Mechanical Behavior Across Length Scales
||Amorphization: A New Dislocationless Deformation Mechanism?
||Marc A. Meyers, S Zhao, Eric Hahn, Boya Li, Bruce A. Remington, Chris Wehrenberg, Hye-Sook Park
|On-Site Speaker (Planned)
||Marc A. Meyers
Intermetallics and covalent materials often exhibit high Peierls-Nabarro stresses and are therefore brittle: the energy to create and propagate cracks is lower than the one to generate the stacking faults, twins, and dislocations required for plastic deformation. Shock compression subjects materials to a unique regime of high hydrostatic and coupled shear stresses for durations on the order, in the case of laser-driven events, of 1-10 nanoseconds. The superposed hydrostatic pressure impedes the formation of cracks. Here we propose that shock/shear amorphization observed in Si, Ge, B4C, and SiC is a new deformation mechanism in a broad class of covalently bonded materials and some intermetallics. The crystalline structure transforms to a higher-density amorphous one along regions of maximum shear stress, forming nanoscale bands, thereby relaxing the shear component of the imposed shock stress. This process is preceded by the emission and propagation of a critical concentration of stacking faults. Molecular dynamics calculations confirm the new mechanism.