High strain rate response of nacre-inspired B₄C/2024Al composites created via bidirectional freeze casting combined with pressure infiltration

Bidirectional freeze casting combined with pressure infiltration has demonstrated significant potential as an effective approach for fabricating bioinspired lamellar composites with excellent strength and toughness. However, their dynamic mechanical response remains underexplored. In this study, B₄C/2024Al composites with long-range ordered nacre-like architectures were fabricated using bidirectional freeze casting followed by pressure infiltration. The mechanical properties and deformation behavior under both quasi-static and dynamic compression conditions were systematically investigated. The results reveal that dynamic compressive strength and strain were significantly higher than their quasi-static counterparts, largely attributed to strain rate hardening and localized matrix melting. Compared to unidirectionally structured composites, the bidirectionally structured ones exhibited superior mechanical performance, achieving a maximum compressive strength of 1088.6 MPa at a strain rate of 3000 s⁻¹ (40 vol% B₄C/2024Al composite). A clear dependence of flow stress and energy absorption capability on B₄C volume fraction was observed. As B₄C content increased, the compressive strength rose, but dynamic strain energy density showed a decreasing trend beyond 20 vol% due to reduced ductility. Specifically, the energy density peaked at 133.08 MJ/m³ for the 20 vol% composite and declined with further ceramic addition, indicating a trade-off between strength and impact energy absorption. The enhanced toughness under dynamic loading is primarily attributed to adiabatic shear localization in the aluminum matrix, which facilitates localized softening and strain accommodation. Additional contributions include crack deflection and branching within the hard ceramic layers, as well as plastic deformation and thermal softening-induced toughening mechanisms in the metallic phase. These findings highlight the promise of nacre-inspired B₄C/Al composites for advanced lightweight armor systems, offering an optimized balance between strength, toughness, and energy absorption under high-strain-rate loading.