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Jian Wang1 Kaisheng Ming1 Qing Su1 Michael Nastasi1

1, University of Nebraska–Lincoln, Lincoln, Nebraska, United States

Radiation induced damage in the core structural materials that are made of crystalline materials are microstructural/crystal defects. Conceptually, these defects can be visualized as regions where there is either a deficiency of lattice atoms (voids, vacancies, edge dislocations, vacancy type dislocation loops) or an excess of lattice atoms (self interstitial atoms, interstitial type dislocation loops). All these defects lead to changes in the mechanical properties of the material. For example, radiation induced swelling (by vacancies and voids) causes dimensional distortion and embrittlement, and is a life-limiting materials issue for structural materials in nuclear power reactors. Austenitic steels were used in fast reactors but could not reliably serve beyond ~150 dpa. Ferritic and ferritic-martensitic (FM) steels have been found to swell much less than austentitic steels. Nano-structuring of both austenitic and FM steels appears to be a promising avenue for further improvement of swelling resistance, providing such structures are stable under ion irradiation. Advanced oxide dispersion strengthened alloys were found to be a promising core structural material, but amorphization and dissolution of oxide particles under high dpa irradiation challenges potential applications. Interfaces (interphase boundaries and grain boundaries) between the metal matrix and nanoscale oxides in oxide dispersion strengthened (ODS) steels systems prove to benefit swelling resistance and creep resistance. Nanoscale metallic interfaces have shown strong defect sink strength and the ability to suppress He bubble formation. However, all of these do not change the intrinsic issue — radiation induced damage in crystalline materials. Compared to crystalline solids, amorphous materials possess no translational symmetry, and amorphous materials do not contain conventional crystal defects such as vacancies, interstitials, or dislocations.
There are two unique radiation effects which must be considered for the irradiation response of amorphous materials: thermal spike formation associated with damage cascades. Another effect is from creation of excessive free volume along an ion track, particularly in the damage cascade core which is rich in open volume temporally due to ballistic collisions. The excessive free volume can thermally enhance atomic mobility and initialize correlated movements needed for crystal nucleation. To prevent crystallization of amorphous associated with the two unique radiation effects, ceramics with high crystallization temperatures is a promising candidate. However, such kinds of amorphous ceramics often exhibit high strength without measurable plasticity. Based on our recent discovery – extreme irradiation-tolerant amorphous Fe-SiOC ceramics that achieve a superior strength-plasticity combination. In this talk, we report our recent discoveries and understanding regarding strength, plasticity, and irradiation properties of amorphous ceramics containing nano-sized metal additions.

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