The foundational MEDE program scientific grand challenges are determining the energy dissipative mechanisms at the atomic, microstructure and macrostructure scales that together contribute to the deformation, damage and failure of materials in extreme dynamic environments. The preexistence and/or impact formation of atomic scale intra-granular planar features may significantly contribute to energy dissipation mechanisms and related computational challenges. There are two general categories of planar features, mostly identified as twins: pre-existing processing related composition modified lamellar, Wadsley-type defects and the formation of planar deformation features (PDFs) in a high stress event, the most common of which is nano-amorphization. Past results have seemed to demonstrate that the presence of apparent “twinning” seem to affect the thermoelectric, thermal conductivity and hardness properties. It has been established that boron rich boron carbide has significantly more planar features. Using analogies to Magneli Ti-O phases, the AlN-Al2O3 system and 1950’s B-C phase diagrams, it will be suggested that the boron carbide “solid solution” may be mixtures of B12C3 and B13C2 phases caused by local electronic instability. Amorphous lamellae (sometimes referred to as “Diaplectic” glass) in minerals (mostly quartz) have been known for some time, and have been used to identify meteor craters. The still, apparently unresolved question is if the glass is the result of a quenched liquid or a solid-solid transformation. Theoretical calculations of 3D crystallographic elasticity ellipsoids by Qinglei Zeng using the Taylor et al (2012) elastic constants show a significant increase in elastic anisotropy at elevated pressures starting at 20 GPa which could lead to shear softening and localization, forming shear bands and/or solid amorphization or melting and quenching to a glass, triggered by a violation of the Born stability criteria.
2021-04-07 08:00:00
