Synergy and competition in nano- and micro-design of structural ceramics

Nanosized structural ceramics SiC and Al2O3–SiC composites were produced and studied in order to define relationships among microstructures (in the micro- and nano-size range) and mechanical properties. In both the systems, no evident improvement in strength and toughness was associated to nano-structures in comparison to micro-structures. However, nano-indentation tests on liquid-phase sintered SiC reveal peculiar and distinctive properties of nanostructured ceramics that imply unexpected repercussions for application performances involving the contact between two materials. Al2O3–SiC nano-composites have lower friction coefficient and higher wear resistance than the pure alumina. The advantages of nano-ceramics are attributed either to the higher grain boundary strength, as in the case of the nano-composites or to surface-dependent deformation mechanisms, like grain boundary sliding, in nanosized monolithic ceramics.