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

Based on the analysis on structure of natural biomaterials, two binds of ce ramic composites with high toughness have been designed and prepared: one i s fibrous monolithic Si3N4/BN composite imitating bamboos or trees in struc ture, the other is laminated Si3N4/BN composite imitating nacre in structur e. Plastic forming methods, including extrusion and roll compaction, respec tively, followed by hot-pressed sintering are used to prepare these two mat erials with particular structures. Both of the two composites have high val ues of fracture toughness and work of fracture: fracture toughness are 24 M Pa m(1/2) and 28 MPa m(1/2), respectively, for fibrous monolithic and lamin ated Si3N4/BN composites, and works of fracture are both more than 4000 J/m (2). The load-displacement curves reveal that these two materials with biom imetic structure exhibit non-brittle feature when applied load to fracture. Through analysis on fractographs of the materials, it is revealed that hig h toughness comes from the synergistic toughening among multi-level toughen ing mechanisms in different scales: weak interfaces, whiskers and elongated grains toughening in ceramic matrix cells. (C) 2000 Published by Elsevier Science S.A.