Centrifugal directional freezing and pressure infiltration: Tailoring gradient structures and mechanical properties in Al/B4C composites

Inspired by the gradient structures found in natural materials like bone, this study presents a novel fabrication method combining centrifugal freeze casting and pressure infiltration to produce Al/B₄C composites with a tunable gradient layered structure, effectively addressing the challenge of achieving both high strength and toughness in metal-matrix composites. By precisely controlling key parameters such as centrifugal speed, ceramic content, particle size distribution, and freezing temperature, we achieved a gradient transition from high hardness and strength in the outer layers to lower hardness and higher toughness in the inner layers, mimicking the performance characteristics of natural materials. Specifically, higher centrifugal speeds and multi-sized ceramic particles promoted a more pronounced gradient structure, with larger particles concentrating in the outer regions for enhanced strength. While increasing ceramic content improved overall strength, it also affected toughness, highlighting the need for optimization. Freezing temperature influenced the ice-crystal structure and interlayer ceramic bridging, impacting both the gradient and overall composite properties. The optimized composites exhibited a unique combination of low density, high strength, and exceptional fracture toughness, primarily attributed to strong interfacial bonding, effective crack deflection and metal bridging, and formation of an interpenetrating structure. This study provides a versatile, cost-effective and scalable pathway for fabricating bioinspired high-performance metal–ceramic composites.