Fei Li

Silicon carbide (SiC) ceramics normally exhibit high hardness but suffer from inherent brittleness, limiting their applications in extreme environments. Traditional strengthening strategies that enhance mechanical strength generally result in the sacrifice of fracture toughness, leading to the typical “strength‐toughness trade‐off”. Here, we report a dual‐strengthening strategy that simultaneously boosts hardness, compressive strength, and fracture toughness of SiC ceramic through the synergistic nanocrystallization and coherent interface effects. Using a polycarbosilane precursor‐derived approach, a HfC‐reinforced SiC ceramic has been fabricated via the in situ crystallization of amorphous SiC intermediate during fast hot‐pressing sintering. The rapid heating enables the direct transformation from amorphous to nanocrystalline SiC matrix, which inhibits the over growth of SiC grain while simultaneously forming coherent HfC/SiC interfaces characterized by aligned crystallographic orientations. Such coherent interfacing between HfC and SiC phases contributes to their strong atomic‐level bonding and thus facilitates effective fracture energy transfer during loading. The resulting SiC ceramic composite containing 20 wt% HfC shows significant mechanical property improvements with Vickers hardness increasing by 20%, compressive strength increasing by 53% and fracture toughness enhancing by 36% compared to pure nanocrystalline SiC ceramic. The simultaneous enhancement of mechanical strength and fracture toughness, together with the improved hardness, demonstrates the synergistic effect of nanocrystallization strengthening and coherent interface reinforcement. This precursor‐derived in situ crystallization strategy provides a promising route for designing advanced composite ceramics with superior mechanical performances.

Prismatic SiC fibers with periodic serrated structure, mostly reaching millimeter‐sized lengths, were synthesized by a simple catalyst‐free method. The process involved heating SiC nanopowder in a graphite crucible at 1700°C under 0.1‐MPa argon atmosphere. The synthesized SiC products consist of SiC fibers several millimeters in length and mostly 0.5–3 µm in diameter. Further, the vapor‐solid growth mechanism and detailed growth process of SiC fibers are discussed. The millimeter‐sized prismatic SiC fibers have the potential to be applied in fields such as electromagnetic wave absorption.