Improved toughness in nanocrystalline ceramics by grain boundary energy engineering

Reference Presenter Authors
09-029 Ricardo Hauch Ribeiro Castro Castro, R.H.(University of California - Davis); Bokov, A.(University of California - Davis); Zhang, S.(University of California - Davis); Faller, R.(University of California - Davis); Dillon, S.(University of Illinois Urbana-Champaign); Feng, L.(University of Illinois Urbana-Champaign); Reduction of grain size has been theoretically predicted to promote toughness enhancement by allowing plastic flow along grain boundaries, but most nanocrystalline ceramics lack the predicted high fracture toughness as a result of the chemical nature of grain boundaries that does not allow for stress accommodation, but rather facilitates crack propagation, such their toughness is not significantly different from normally brittle microcrystalline counterparts. Here we demonstrate that a refined control of the grain boundary chemistry and energy landscape can lead to largely improved toughness by allowing maneuvering of nanocrack formation and hence increased crack deflection and toughness. By combining Monte Carlo simulations, experimental thermodynamics by microcalorimetry, and in-situ transmission electron microscopy cracking visualization, we report that rare-earth doping at the grain boundaries decreases the local excess energies and dampens anisotropy (i.e. the energy difference between boundaries), thus smoothing out the energy landscape across the nanocrystalline sample. These causes multiple crack deflection and offer a non-system-specific versatile approach to improve toughness of single-phased ceramics nanostructures.
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