Consolidation–microstructure–property relationships in bulk nanoceramics and ceramic nanocomposites: a review

Abstract

The recognition that bulk nanoceramic materials, having grain sizes typically 100 nm or finer, possess appealing mechanical, physical and tribological properties has generated considerable recent research activity. A major challenge in the research on bulk nanoceramics and nanoceramic composites is concerned with the aspect of processing, in particular restriction of grain growth during sintering. In this regard novel processing techniques have been developed with the aim of fabricating bulk ceramic nanomaterials. The superior properties exhibited by these bulk nanoceramics and ceramic nanocomposites, compared with conventional ceramic materials, have opened up prospects for their use in applications demanding better mechanical properties. The present review highlights outstanding issues related with the processing of nanoceramics and ceramic nanocomposites, discusses the novel processing techniques currently used to develop these materials, critically analyses the property modifications resulting from microstructural refinement and provides an overview of the structure-property correlations of some recently developed bulk nanoceramic materials. Potential fields of application for ceramic nanomaterials are surveyed. In conclusion, the unresolved issues related to bulk nanoceramic processing are considered and a perspective is given of areas of future research.

Micromechanics of fracturing in nanoceramics

“…Fracture processes in nanoceramics are crucially influenced by grain and interphase boundaries whose amounts are very large in these materials [1][2][3][4]. So, grain and interphase boundaries serve as preferable places for nanocrack nucleation and growth, because the atomic density is low, and interatomic bonds are weak at boundaries compared with the bulk phase.…”

“…Although high-strength nanoceramics are commonly brittle, there are experimental data indicative of enhanced fracture toughness exhibited by several special nanocrystalline ceramics at comparatively low homologous or moderate temperatures (e.g. reviews [1,2,4], book [3] and original papers [8][9][10][11][12][13]19]). These experimental data are logically explained within the concept that (i) conventional toughening micromechanisms (that dominate in microcrystalline-matrix ceramics) operate in specific, inherent to nanostructures, ways in nanocrystalline ceramics where they effectively hamper crack growth and (ii) new, special (inherent to nanocrystallinity) toughening micromechanisms come into play in nanocrystalline ceramics [30][31][32][33][34][35][36][37][38][39][40][41][42][43].…”

“…The ductile behaviour of materials is highly desired for a wide range of technologies. Nanoceramics are commonly brittle at room temperature [1][2][3][4], as with their coarse-grained counterparts. Brittle fracture dominates in ceramic materials, first of all, because lattice dislocation slip (the key deformation mechanism responsible for ductile behaviour exhibited by most metallic solids) is suppressed in ceramics at room temperature.…”

“…pioneering papers [21,27,28] and reviews [1,2]). In particular, values of strength for ultrafine-grained and nanocrystalline ceramics at room temperature can be two to five times higher than those of microcrystalline ceramics [1,2,21,27,28].…”

“…pioneering papers [21,27,28] and reviews [1,2]). In particular, values of strength for ultrafine-grained and nanocrystalline ceramics at room temperature can be two to five times higher than those of microcrystalline ceramics [1,2,21,27,28]. Such high values of strength of nanoceramics are considered to occur owing to the combined effects of several factors, such as reduction in flaw sizes (close to nanoscale grain sizes in nanocrystalline structures) and structural homogenization (resulting in a partial release of residual stresses resulted from the sintering process).…”