Nanostructured ceramics can change our view on ceramic mechanical properties. Lately several studies have shown plastic behavior in ceramic nanoparticles and bulk samples even at low temperatures. Traditionally based on the Griffith criterion, fracture toughness of ceramics has been improved for example by lowering the size of the internal flaws, by bridging the forming crack by fibre addition, or by tailoring a rod-like grain structure for the material inducing a crack bridging effect. Most notably, the stress induced phase transformation of ZrO2 has been successfully applied to improve fracture toughness of advanced ceramics.
One way to improve the fracture toughness of ceramics, that is not included in the Griffith criterion, is to allow plastic deformation of the ceramic structure. Already in 1987, Karch et al. suggested in Nature that by lowering the grain size of a bulk ceramic material down to few nanometers, the deformation behaviour could change from brittle to ductile even at low temperatures.
Currently, I am studying the mechanical limits of these nanostructured ceramics by using in situ transmission electron microscopy. This enables us to manipulate (compression/tension) the sample in real time while imaging the deformation mechanism.
This will allow us to understand how these new materials behave under stress and whether we could increase the ductility of ceramics close to that of metals.
TEM image of a typical compression test setup