Compared to polycrystalline materials, nanocrystalline (nc) materials are expected to exhibit superior radiation resistance due to the presence of a large volume fraction of grain boundaries (GB), which can act as sinks for point defects. Although the enhanced radiation resistance of nc materials has been supported by many recent experiments, there also exist reports of contrary observations. Consequently, understanding of the interactions of radiation-induced defects with GBs is essential for designing radiation-tolerant nc ceramics for advanced nuclear applications. Using SiC as a model covalent ceramic we demonstrate that the grain size effects during irradiation are strongly coupled to defect energy landscape. For example, we discovered that the presence of recombination barriers in nc ceramics can lead to the interstitial starvation. In this phenomenon interstitials are prevented from recombining with vacancies due to high recombination high barriers, and instead interstitials migrate to GBs where they are annihilated. As a result, there is a crossover with an increasing temperature from the regime where nc materials are more radiation resistant to the regime where their radiation resistance is inferior as compared to the coarse-grained material. We will also present our results on the effects of GB stresses on the sink strength. Sink strength of GBs is a measure of GB efficiency in annihilating point defects. Most previous models of GB sink strengths have ignored the effects of GB stress on the rate of defect annihilation. We found that while for coarse-grained materials the effects of the stress field are negligible, GB stresses play a significant role in the kinetics of defect annihilation in fine-grained materials. Contrary to what has been established for larger grain size, in nanomaterials small angle GB can annihilate defects faster than large angle GB. Finally, we will also discuss our newly discovered criterion for defect-induced amorphization in carbide ceramics.

Interactions of radiation-induced defects with grain boundaries in covalent ceramics

247th National Meeting (2014)

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