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

Abstract

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.

Anisotropy of Mechanical Properties in a Hot‐Pressed Boron Carbide

“…Several theoretical studies have shown that the strain rate dependence of the peak (failure) stress of brittle materials is strongly dependent on the characteristics of such defects . The rate dependence was also observed experimentally in many advanced ceramics, including BC …”

Microstructure Evolution of Titanium Nitride Film during Vacuum Kinetic Spraying

“…Ceramics are generally brittle at room temperature, however, plastic deformation of alumina, aluminum nitride, silicon carbide, boron carbide, and zirconia at extreme loading conditions, such as in high‐pressure compression, indentation, and shockwaves, has been observed . Chen et al .…”

“…Chen et al . observed that plastic deformation‐induced twins were activated when a stress higher than the Hugoniot elastic limit (HEL) was reached in alumina . Extensive dislocations were observed at the impact surface of silicon carbide at pressure exceeding its HEL .…”

Amorphization‐induced volume change and residual stresses in boron carbide

“…These anomalies in the high‐pressure performance of boron carbide spurred numerous investigations into the evolution of short‐range disorder in the material, often referred to as “amorphization”. Subsequent studies have also documented amorphization under Berkovich and Vickers indentations, laser shock impact, mechanical scratching, and nonhydrostatic loading in diamond anvil cell experiments . Postmortem TEM of the deformed regions revealed inhomogeneous distributions of nanoscale amorphized zones within the crystalline matrix of boron carbide …”