Influence of stress state and strain rate on structural amorphization in boron carbide

摘要

The reduced performance of B4C armor plate for impact against tungsten carbide penetrators beyond a critical velocity has been attributed in the literature to localized amorphization. However, it is unclear if this reduction in strength is a consequence of high pressure or high velocity. Despite numerous fundamental studies of B4C under indentation and impact, the roles of strain rate and pressure on amorphization have not been fully established. Toward this end, rate dependent uniaxial compressive strength and rate dependent indentation hardness, along with Raman spectroscopy, have been employed to show that high strain rate deformation alone (without concurrent high pressure) cannot trigger localized amorphization in B4C. Based on our analysis, it is also suggested that rate dependent indentation hardness can be used to reveal if a given B4C ceramic exhibits amorphization under high pressure and high strain rate loading. It is argued that when amorphization does occur in B4C, its dynamic inelastic properties degrade more severely than its static properties. Finally, it is suggested that dynamic hardness, in conjunction with static hardness, can be used as a measurable mechanical property to reveal the incidence of amorphization in B4C without the need for postmortem TEM or Raman spectroscopy analyses.