The ultimate goal of studying themicrostructure of Mollusk shells is the manufacturing of composite materialswith superior mechanical properties like high elastic modulus, strength andtoughness. Nevertheless, fabrication of synthetic versions of the crossed lamellarstructure has been exploited on a limited scale. The first attempt was fromChen et al. (2004) who used MEMS (micro-electro-mechanical systems) processingmethods to fabricate two ceramic/polymer crossed-lamellar composites, aBN/epoxy and a BN/EW160Aglass/epoxy specimen The impact fracture toughness ofthe specimens increased compared with that of monolithic ceramics.
Kaul and Faber (2005) created aprocess to produce a crossed-lamellar microstructure in mullite combining tapecasting, oriented lamination and templated grain growth. The composition of thecomposite material was 82% 3Al2O3•2SiO2, 12% 9Al2O3•B2O3whiskers and 6% TiO2 (for densification). Ceramic laminateswere produced with aligned rod-like grains with the alignment direction varyingfrom layer to layer with abrupt interfaces. Each layer was analogous to 1st-orderlamellae and rod-like grains to 2nd-order lamellae. The temperaturefracture of this material resulted ina tortuous crack paths as propagationchanged directions as grain alignment shifted across ±45º interfaces (fig2).The Sequential HierarchicalEngineered Layer Lamination (SHELL), developed by Karambelas et al (2013), is athermoplastic forming process capable of producing the hierarchicalmultilayered crossed-lamellar architecture of Strombus Gigas conch shell. Thefabrication of the silicon nitride-boron nitride Si3N4(matrix), h-BN (fibers) ceramics initiated by forming the basic building unitvia sequential co-extrusion of the bulk and interface materials.
With a singlecutting and rotation operation, layer XY (the virgin extrusion configuration)can be reconfigured into layers XZ and YZ with one of them being the weak”tunnel” cracking layer. The remaining layers, the XYZ 2nd and 3rd-orderlayers with alternating orientations ±45º, are produced by additional cuttingand rotational steps to achieve the full three dimensional variation ininterfaces. Toughening mechanisms like Strombus’ Gigas were observed; tunnelcracking in the 1st-order interfaces, crack bridging and fiber-likesliding (fig3,4).A promising ultrahightemperature crossed-lamellar structure in the (Mo0.85Nb0.
15)Si2C40/C11btwo-phase crystal was developed by Haghihara et al (2017). Rod-like C11b phasegrains along a direction perpendicular to the lamellar interface were developedin addition to fine lamellae. The mother alloy with chemical composition of (Mo0.85Nb0.
15)0.97Cr0.015Ir0.015 Si2 was prepared with arc melting of highpurity raw metals in an Ar atmosphere. Single crystals with C40 structure (bodycentered cubic lattice) were grown using an optical FZ furnace in an Ar gasflow.
Those crystals were then annealed at 1400ºC in an Ar atmosphere todevelop the two-phase microstructure composed of the C40 and C11b () phases. Atthe beginning part of the CrIr-added crystal a fine lamellar microstructure wasobserved. At the upper part of that crystal a unique microstructure whichcontained many C11b phase grains that extended along the directionperpendicular to the microstructure had been developed. Those grains acted asan “anchor” preventing the occurrence of catastrophic failure by fiberbridging.
Fracture toughness increased in all loading directions andhigh-temperature strength was effective in increasing creep resistance