Date(s) - 09/29/2020
3:00 pm - 4:00 pm
Ricardo Castro, Ph.D.
Associate Dean, Research and Graduate Studies
Professor, Material Science and Engineering
University of California, Davis
Nanoscale materials are different from their bulk counterpart not only because they are small, but because a large fraction of their atomic volume belongs to the interfacial regions. This leads to significant properties of nanomaterials being governed by the different levels of complexities emerging from interfacial atoms. In nanoceramics, this implies that grain boundary characteristics are key parameters for understanding and controlling properties. Although one can analyze grain boundaries from several perspectives, a thermodynamic analysis can provide an ‘all-inclusive’ parameter because it naturally reflects physical-chemical and mechanical stresses.
In this talk, founded on recent data on grain boundary energies obtained by rigorous microcalorimetric experiments, we discuss the role of grain boundary energies as a designing tool to improve mechanical properties of nanoceramics. By using yttria-stabilized zirconia as a model system, we show first the direct relationship between hardness and the observation of an inverse-Hall-Petch relationship with the fact grain boundary energies systematically increase with decreasing grain size below 30nm. Furthermore, we demonstrate that grain boundary energies can be purposefully modified by using dopants prone to segregation, providing a useful instrument to tune mechanical behavior. By introducing lanthanum, we show not only the absolute grain boundary energy is affected by the dopant, but the existing grain boundary distribution as well, leading to macroscopic impacts on the toughness of nanoceramics by crack deflection mechanisms. The results suggest grain boundary engineering is possible in nanoceramics, although in a different manner as proposed in the metallurgy literature.