Directional amorphization of boron carbide subjected to laser shock compression

• Published in: Proceedings of the National Academy of Sciences - PNAS 2016-10, Vol.113 (43), p.12088-12093
• Main Authors: Zhao, Shiteng, Kad, Bimal, Remington, Bruce A., LaSalvia, Jerry C., Wehrenberg, Christopher E., Behler, Kristopher D., Meyers, Marc A.
• Format: Article
• Language: English
• Subjects: amorphization; Boron; boron carbide; Carbides; Energy conversion; Heat transfer; lasers; MATERIALS SCIENCE; Physical Sciences; Propagation; Shear stress; shock wave; Shock waves; Strain rate; Thermal energy; Wave propagation
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1604613113

Solid-state shock-wave propagation is strongly nonequilibrium in nature and hence rate dependent. Using high-power pulsed-laser-driven shock compression, unprecedented high strain rates can be achieved; here we report the directional amorphization in boron carbide polycrystals. At a shock pressure of 45∼50 GPa, multiple planar faults, slightly deviated from maximum shear direction, occur a few hundred nanometers below the shock surface. High-resolution transmission electron microscopy reveals that these planar faults are precursors of directional amorphization. It is proposed that the shear stresses cause the amorphization and that pressure assists the process by ensuring the integrity of the specimen. Thermal energy conversion calculations including heat transfer suggest that amorphization is a solid-state process. Such a phenomenon has significant effect on the ballistic performance of B₄C.