Stress-induced amorphization of boron carbide has been extensively explored via various experimental and theoretical studies since its initial discovery about twelve years ago. However, several fundamental behaviors are still not well understood and there has not yet been a thorough effort made to understand the initiation and growth of nanoscale amorphous bands and their importance with respect to damage evolution and eventual fragmentation. In this work, fragmentation features in a ballistically-impacted, commercially-available, and monolithic boron carbide were examined by scanning electron microscopy (SEM) and aberration-corrected scanning transmission electron microscopy (ac-STEM). Furthermore, site-specific in-situ focused ion beam sample preparation was conducted to directly compare microstructure features at different locations within the failure zone. A key finding was that oxidized and pristine boron carbide were observed near and far from the impact surface, respectively. In addition, nanoscale amorphous bands extending from concentrated stress regions such as particle-particle contacts were observed thereby providing direct evidence for the role of stress-induced amorphization on damage evolution and fragmentation under non-hydrostatic compression conditions. Experimental procedures, results, and analyses are presented.
