Role of Pressure and Strain Rate in Structural Amorphization in Boron Carbide
Ghatu Subhash (University of Florida), Dipankar Ghosh (California Institute of Technology)
Materials for Extreme Environments: Multiscale Experiments and Simulations
Mon 2:40 - 4:00
Salomon 203
Localized amorphization has been identified as the mechanism for the reduced performance of B4C armor plates during impact against tungsten carbide penetrators when the impact velocity exceeds a critical velocity. However, it is unclear if this reduction in strength is a consequence of high pressure or high velocity. Towards this end, rate dependent uniaxial compressive strength and rate dependent indentation hardness, along with Raman spectroscopy, have been employed on two ceramics (B4C and SiC) to show that high strain rate deformation alone (without concurrent high pressure) cannot trigger localized amorphization in B4C. While high pressure is essential, the high rate deformation accelerates and lowers the threshold stress for amorphization. It is also argued that when amorphization does occur, the dynamic inelastic properties degrade more severely compared to the 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 phase transformation in B4C without the need for any postmortem TEM or Raman spectroscopy analyses. To further understand the mechanics of amorphization process, an in-depth study to map the 3D amorphized zone beneath an indentation is carried out. The spatial distribution in intensity of amorphzation is measured to gain insight into the characteristics of amorphization zone. The implications of these results to ballistic performance of B4C armor plates will be discussed.