Biomimetic structure design — a possible approach to change the brittleness of ceramics in nature

Based on the analysis on structure of natural biomaterials, two kinds of ceramic composites with high toughness have been designed and prepared: one is fibrous monolithic Si3N4/BN composite imitating bamboos or trees in structure, the other is laminated Si3N4/BN composite imitating nacre in structure. Plastic forming methods, including extrusion and roll compaction, respectively, followed by hot-pressed sintering are used to prepare these two materials with particular structures. Both of the two composites have high values of fracture toughness and work of fracture: fracture toughness are 24 MPa m1/2 and 28 MPa m1/2, respectively, for fibrous monolithic and laminated Si3N4/BN composites, and works of fracture are both more than 4000 J/m2. The load-displacement curves reveal that these two materials with biomimetic structure exhibit non-brittle feature when applied load to fracture. Through analysis on fractographs of the materials, it is revealed that high toughness comes from the synergistic toughening among multi-level toughening mechanisms in different scales: weak interfaces, whiskers and elongated grains toughening in ceramic matrix cells.