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.