Deformation in Nanocrystalline Ceramics: A Microstructural Study
23 Pages Posted: 3 Jul 2019 First Look: Accepted
Contrary to the characteristic strengthening of polycrystalline ceramics with a decrease in grain size, extremely fine nanocrystalline ceramics exhibit softening, increased plasticity and sometimes an inverse Hall-Petch relation. Despite experimental evidence, questions remain regarding the underlying deformation mechanisms governing this abnormal mechanical behavior. In the present study, an in-depth microstructural examination was performed on nanostructured transparent magnesium aluminate spinel (MgAl2O4) subjected to microhardness tests. Microstructural observations revealed regions strained to various degrees below the point of indentation, containing varying amounts of dislocations and nano-cavities. Furthermore, the residual strain in different areas was estimated by local electron diffraction. This provided evidence supporting the roles of both dislocation motion and grain boundary sliding (GBS) mechanisms. Moreover, shear bands formed and were found to be associated with micro-cracking. By combining the microstructural analysis with suitable models, it was concluded that these mechanisms govern plastic deformation. By elucidating how strain is accommodated within nanocrystalline ceramics, a deeper understanding of their unique mechanical behavior is gained.
Keywords: nanocrystalline ceramics, indentation, dislocations, grain boundary sliding, shear bands
Suggested Citation: Suggested Citation