SUN Mengyong, QU Junfeng, FANG Hairong, LI Guobin, WANG Wenlong, WANG Honglin, GUO Min, YIN Fei

(Inner Mongolia Institute of Metal Materials, Baotou 014000, Inner Mongolia, China)

Extended abstract:[Background and purposes] The evolution of protective armor, driven by advancing weaponry, has shifted towards multi-material composites. Ceramics, notably alumina (Al₂O₃), silicon carbide (SiC) and boron carbide (B₄C), are pivotal components, due to their low density, high hardness, modulus, melting point, and strength, significantly enhancing ballistic protection for personnel and vehicles. While Al₂O₃ is denser and B₄C is costlier, SiC ceramics have emerged as a primary choice owing to their combination of low density, cost-effectiveness and superior ballistic performance. Understanding the dynamic response of ceramics under extreme impact loading, characterized by GPa-level stresses, millisecond durations and localized effects, is crucial but remains challenging. Research focuses on ballistic mechanisms, dynamic damage evolution and constitutive relationships under such high-strain-rate conditions, yet limitations in testing methods hinder full comprehension of transient dynamic behavior. Given SiC's critical role, investigating its stress response and failure mechanisms under dynamic impact is paramount. This study was aimed to specifically examine the influence of interface types within SiC ceramics on their impact resistance. By fabricating SiC ceramics with varied interfaces and employing Split Hopkinson Pressure Bar (SHPB) testing, it was attempted to elucidate the dynamic mechanical behavior and damage mechanisms under impact, thereby revealing how interface characteristics govern the material's anti-penetration performance.[Methods] SiC ceramics were fabricated with SiC, B₄C, C, B, Al₂O₃ and Y₂O₃ powders (1–3 μm, >99% purity), with specific sintering additive ratios. The powders were ball-milled for 12 h in a solvent mixture of alcohol and methyl ethyl ketone, with TEP as dispersant, PVB as binder and glycerol as plasticizer, to form a homogeneous slurry. A slurry with 40 wt.% solid content was tape-cast using doctor blade set at 0.6 mm and 0.9 mm. The dried tapes were cut, stacked and laminated at 30 MPa and 120 ℃. After debinding, the samples were sintered. The sintered ceramics were characterized by using Archimedes' method for density, SEM for microstructure, Vickers hardness testing at 9.8 N and three-point bending for strength and fracture toughness. Dynamic mechanical properties were evaluated using a split Hopkinson pressure bar to obtain stress-strain curves and analyze strain rate effects, energy absorption and damage evolution mechanisms.[Results] Liquid-phase sintered (L-SiC) ceramics exhibited the highest fracture toughness, due to energy absorption by weak grain boundary phases. Both L-SiC and reaction sintered (R-SiC) ceramics showed higher flexural strength than the solid-phase sintered samples (S-SiC), which suffered from reduced mechanical properties related to the closed pores and large grains. S-SiC, with strong interfaces and fewer grain boundary phases, had the highest hardness. Microstructural analysis revealed that L-SiC consists of SiC grains and YAG intergranular phase, failing primarily through intergranular fracture and YAG phase failure. S-SiC, containing SiC grains, residual carbon and closed pores, failed mainly by transgranular fracture. R-SiC, composed of SiC, B₄C and Si, failed primarily through fracture of the Si phase and intergranular fracture. Under dynamic compression, all ceramics showed significant strain rate strengthening. The flow stress increased with strain rate, with S-SiC having the highest strength, followed by L-SiC and R-SiC. The failure time decreased with increasing strain rate. Energy absorption analysis indicated that transmitted energy decreased while reflected and dissipated energy generally increased with strain rate. The variation was attributed to the rapid loss of structural integrity. S-SiC demonstrated the strongest ability to maintain structural integrity at low strain rates. Dynamic damage analysis showed that, at low strain rates, breaking produced larger fragments, while high strain rates resulted in fine debris. S-SiC and R-SiC fragments exhibited more pronounced prismatic morphology than L-SiC, where weak interfaces caused crack deflection. Microscopic examination of fracture surfaces revealed intergranular fracture with grain pull-out in L-SiC, transgranular fracture in S-SiC and brittle fracture of the Si phase with limited crack extension in R-SiC. Under ultra-high strain rates, micro-cracks are formed within S-SiC grains, indicating internal damage and plastic deformation, due to the residual stresses from elastic anisotropy.[Conclusions] Three types of SiC ceramics with distinct interfaces were fabricated, each exhibiting characteristic failure modes. The liquid-phase sintered sample (L-SiC) failed mainly through intergranular fracture and failure of the YAG grain boundary phase, the solid-phase sintered sample (S-SiC) failed primarily via transgranular fracture and the reaction sintered (R-SiC) one failed through fracture of the Si phase combined with intergranular fracture. All the three ceramic types exhibited a significant strain rate strengthening effect. The interface type influenced the flow stress, i.e., weak interfaces reduced the flow stress but increased the failure strain, whereas strong interfaces enhanced the flow stress but decreased the failure strain. The interfacial type, together with the material's ability to maintain structural integrity, jointly influenced the kinetic energy dissipation. Energy was dissipated through mechanisms including particle fragmentation, friction and ejection. Based on the dynamic damage process, the failure of SiC ceramics can be categorized into a three-stage progression.

Key words: silicon carbide; interface type; strain rate effect; dynamic damage