Influence of crystal orientation and polymorphism on the shock response of boron carbide

K Ghaffari and S Bavdekar and DE Spearot and G Subhash, ACTA MATERIALIA, 296, 121305 (2025).

DOI: 10.1016/j.actamat.2025.121305

Despite its exceptional hardness, boron carbide suffers from a strength- limiting deformation mechanism called amorphization under high-pressure loading. The conditions governing amorphous band formation and their propagation remain unresolved. Using molecular dynamics simulations with a newly developed machine-learned interatomic potential, we investigate the influence of crystal orientation and polymorphism on the shock behavior of four boron carbide polymorphs. For the first time, shear- induced amorphous band formation is captured during shock compression, and its growth characteristics are systematically analyzed. We find that amorphous band growth varies with crystal orientation, with 0 degrees and 90 degrees chain alignments exhibiting increased susceptibility compared to 45 degrees and 60 degrees alignments. Crystal orientation also strongly affects the Hugoniot elastic limit (HEL), with chains parallel to the shock direction showing the lowest HEL, contradicting prior literature. Polymorphs with C-B-C chains exhibit enhanced toughness through chain bending and full recovery upon unloading, whereas those with C-C-C chains are prone to failure and cannot revert to their original structure. This behavior is linked to bonding tendencies between chain and icosahedral atoms. Furthermore, when amorphization leads to extensive crystal collapse, atomic packing in open spaces within the rhombohedral structure enables volume shrinkage, triggering fracture initiation. In contrast, localized amorphous band formation induces atomic rearrangement, leading to volume expansion and compressive stresses in the surrounding elastic matrix, aligning with previous predictions. These findings provide new insights into the dynamic response of boron carbide, shedding light on key factors that govern its deformation and failure mechanisms.

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