High-pressure deformation and amorphization in boron carbide

Abstract

Icosahedral boron-rich solids fall second in hardness to diamondlike structures and have been the subject of intense investigations over the past two decades, as they possess low density, high thermal, and mechanical stability at high temperatures, and superior industrial manufacturability. A common deleterious feature called “presssure-induced amorphization,” limits their performance in high-velocity projectile applications. This article discusses spectral characteristics of amorphized states of boron carbide, a common icosahedral boron-rich ceramic, with the goal of understanding the mechanistic layout of pressure-induced amorphization. Mystery has surrounded the appearance of new peaks in Raman spectrum of pressure-induced amorphized boron carbide, but to date, no convincing explanation exists on their origin. Shock studies of boron carbide have proposed phase transformation at high pressures, but to date, no conclusive evidence has been corroborative to prove the existence of new high-pressure phases. We propose a new rationale toward deciphering the amorphization phenomenon in boron carbide centered on a thermodynamic approach to explain atomic interactions in amorphous islands. Quantum mechanical simulations are utilized to understand the impact of stresses on Raman spectra, while results from molecular dynamics (MD) simulations of volumetric compression are used to understand thermodynamic aspects of amorphization. Atomic-level nonbonded interactions from the MD potential are utilized to demonstrate origins of the residual pressure. Combining these efforts, the present study deciphers the connection between deformation behavior of boron carbide at high pressure and its mysterious amorphous Raman spectrum. The approach highlights the importance of meticulously incorporating multiscale modeling considerations in determining accurate material behavior of ultrahard materials.