The composites, a BN/epoxy and a BN/EW160Aglass/epoxy specimen The

The ultimate goal of studying the
microstructure of Mollusk shells is the manufacturing of composite materials
with superior mechanical properties like high elastic modulus, strength and
toughness. Nevertheless, fabrication of synthetic versions of the crossed lamellar
structure has been exploited on a limited scale. The first attempt was from
Chen et al. (2004) who used MEMS (micro-electro-mechanical systems) processing
methods to fabricate two ceramic/polymer crossed-lamellar composites, a
BN/epoxy and a BN/EW160Aglass/epoxy specimen The impact fracture toughness of
the specimens increased compared with that of monolithic ceramics.

Kaul and Faber (2005) created a
process to produce a crossed-lamellar microstructure in mullite combining tape
casting, oriented lamination and templated grain growth. The composition of the
composite material was 82% 3Al2O3•2SiO2, 12% 9Al2O3•B2O3
whiskers and 6% TiO2 (for densification). Ceramic laminates
were produced with aligned rod-like grains with the alignment direction varying
from layer to layer with abrupt interfaces. Each layer was analogous to 1st-order
lamellae and rod-like grains to 2nd-order lamellae. The temperature
fracture of this material resulted ina tortuous crack paths as propagation
changed directions as grain alignment shifted across ±45º interfaces (fig2).

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The Sequential Hierarchical
Engineered Layer Lamination (SHELL), developed by Karambelas et al (2013), is a
thermoplastic forming process capable of producing the hierarchical
multilayered crossed-lamellar architecture of Strombus Gigas conch shell. The
fabrication of the silicon nitride-boron nitride Si3N4
(matrix), h-BN (fibers) ceramics initiated by forming the basic building unit
via sequential co-extrusion of the bulk and interface materials. With a single
cutting 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-order
layers with alternating orientations ±45º, are produced by additional cutting
and rotational steps to achieve the full three dimensional variation in
interfaces. Toughening mechanisms like Strombus’ Gigas were observed; tunnel
cracking in the 1st-order interfaces, crack bridging and fiber-like
sliding (fig3,4).

A promising ultrahigh
temperature crossed-lamellar structure in the (Mo0.85Nb0.15)Si2C40/C11b
two-phase crystal was developed by Haghihara et al (2017). Rod-like C11b phase
grains along a direction perpendicular to the lamellar interface were developed
in addition to fine lamellae. The mother alloy with chemical composition of (Mo0.85Nb0.15)0.97Cr0.015
Ir0.015 Si2 was prepared with arc melting of high
purity raw metals in an Ar atmosphere. Single crystals with C40 structure (body
centered cubic lattice) were grown using an optical FZ furnace in an Ar gas
flow. Those crystals were then annealed at 1400ºC in an Ar atmosphere to
develop the two-phase microstructure composed of the C40 and C11b () phases. At
the beginning part of the CrIr-added crystal a fine lamellar microstructure was
observed. At the upper part of that crystal a unique microstructure which
contained many C11b phase grains that extended along the direction
perpendicular to the microstructure had been developed. Those grains acted as
an “anchor” preventing the occurrence of catastrophic failure by fiber
bridging. Fracture toughness increased in all loading directions and
high-temperature strength was effective in increasing creep resistance