Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “POINT DEFECTS”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

The Influence of Grain Boundaries on Radiation-Induced Point Defect Production in Materials: A Review of Atomistic Studies

Radiation-induced defects cause severe degradation of materials properties during irradiation that can ultimately cause the material to fail. Consequences of these defects include swelling, embrittlement, and undesirable phase transformations. Nanocrystalline materials, which contain a high density of grain boundaries, have demonstrated enhanced radiation tolerance compared to large grain counterparts under certain conditions. This is because, as has long been recognized, grain boundaries can serve as defect sinks for absorbing and annihilating radiation-induced defects. Increasingly, researchers have examined how grain boundaries influence the direct production of defects during collision cascade, the origin of the radiation-induced defects. In this review article, we analyze the computational studies in this area that have been performed during the past two decades. These studies examine defect production near grain boundaries in metallic, ionic, and covalent systems. It is found that, in most systems, grain boundaries absorb more interstitials than vacancies during the defect production stage. While this is generically true of most boundaries, the detailed interaction between defects and grain boundaries does depend on boundary atomic structure, the stress state near the boundary, cascade-boundary separation, and materials properties. Furthermore, the defect distribution near boundaries is qualitatively different from that in single crystals, with the former often exhibiting larger vacancy clusters and smaller interstitial clusters than the latter. Finally, grain boundaries that are damaged after cascades have occurred exhibit different interaction behavior with defects than their pristine counterparts. Together, these atomistic simulation results provide useful insight for both developing higher-level modeling of defect evolution at long timescales and how interfaces influence radiation damage evolution.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Influence of grain boundary character on point defect formation energies in BCC Fe

The objective of this research is to understand how grain boundary character influences formation of vacancies and interstitials to grain boundaries in BCC Fe. In this study, molecular statics simulations were used to obtain a large number of minimum energy grain boundary structures in the <100> and <110> symmetric tilt grain boundary system. Then, simulations were used to calculate the formation energies associated with vacancies and self-interstitial atoms at atomic positions within 20 Angstroms of the boundary. As a first analysis, the vacancy formation energies are examined here. The simulation results show how the vacancy formation energies are influenced by grain boundary structure. Low angle boundaries are found to be an effective sink for vacancies along planes adjacent to grain boundary dislocations, while high angle low sigma grain boundaries are less effective sinks for vacancies. The grain boundary sink strength is postulated to depend upon the minimum vacancy formation energy and the influence of grain boundary character on this is shown. Interestingly, low sigma boundaries in the <100> symmetric tilt grain boundary system have higher minimum vacancy formation energies, while this quantity does not seem to be influenced by misorientation angle or grain boundary energy. The significance of this research is that atomistic simulations of this kind may ultimately help inform damage evolution via grain boundaries in multiscale models for irradiated materials as well as its implications for grain boundary engineering.

BCC Fe↗