Nanostructured Materials for Nuclear Applications II: Session IV
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Nanomechanical Materials Behavior Committee, TMS: Nuclear Materials Committee
Program Organizers: Cheng Sun, Idaho National Laboratory; Khalid Hattar, Sandia National Laboratories ; Celine Hin , Virginia Tech; Fei Gao , University of Michigan; Osman Anderoglu , Los Alamos National Laboratory; Mitra Taheri , Drexel University; Haiming Wen , Idaho State University

Tuesday 2:00 PM
February 28, 2017
Room: Pacific 24
Location: Marriott Marquis Hotel

Session Chair: Haiming Wen, Idaho State University ; Celine Hin, Virginia Tech

2:00 PM  Invited
Stability and Self-ion Irradiation Damage in Nanocrystalline Tungsten and Solute-stabilized Tungsten Alloys: Jason Trelewicz1; 1Stony Brook University
    Tungsten has emerged as the most promising candidate for the high heat flux regions of reactor-scale fusion devices due to its high temperature strength, sputtering resistance, and chemical compatibility with tritium. However, irradiation of tungsten leads to the onset of damage that can limit its technological utility as a plasma-facing material. One approach for enhancing radiation tolerance involves refining the grain size to the nanometer regime. In this work, self-ion irradiation damage in nanocrystalline tungsten was characterized as a function of total dose through in situ electron microscopy techniques using 3 MeV W ions. Defect formation mechanisms were investigated using collision cascade simulations, and employed to explicate the damage evolution trends from experiments. Solute-stabilized nanocrystalline tungsten alloys were finally analyzed under identical irradiation conditions and the damage state contrasted with unalloyed nanocrystalline tungsten to identify design strategies for enhancing their stability and radiation tolerance.

2:30 PM  Invited
The Two-step Nucleation of G-phase in Ferrite: The Critical Size and Composition for the Structural Change of Solute Clusters: Yoshitaka Matsukawa1; Tomoaki Takeuchi2; Yuta Kakubo1; Tomoaki Suzudo2; Hideo Watanabe3; Hiroaki Abe4; Takeshi Toyama1; Yasuyoshi Nagai1; 1Tohoku University; 2Japan Atomic Energy Agency; 3Kyushu University; 4The University of Tokyo
    Empirically, since 1930s, it has been known that the nucleation of second phase precipitates in solids occurs via a two-step process: the first step is a spontaneous growth of solute clusters, and the second step is their structural change. By combining modern atom probe tomography and transmission electron microscopy, we demonstrate that their structural change occurs via another two-step process: the first step is size fluctuation to become a critical size, and the second step is compositional fluctuation to become a critical composition. In the present study, the size growth of solute clusters stopped at the critical size. There was a time lag between the end of size growth and the start of structural change. The incubation period was controlled by solute enrichment inside the clusters. The length of incubation period was several-month-long in the case of the nucleation of intermetallic compound G-phase from ferrite solid solution at 673 K.

3:00 PM  
Period-thickness Dependent Responses of Cu/W Multilayered Nanofilms to Ions Irradiation under Different Ion Energy: Feng Ren1; 1Wuhan University
    In this work, we study the response of the Cu/W multilayers to the irradiation ions with energy varied from 40 keV to 200 MeV. Strong period-thickness dependent response of the multilayers to the ion energy was observed. After He+ ions irradiation, the density of He bubbles in the multilayers increases with increasing of the period-thickness. For 6.4 MeV Xe20+ irradiation to 20 dpa, the interface-mixing appeared in the multilayers with period-thickness larger than 9 nm due to the ballistic mixing and the thermal spike mixing. However, the samples with smaller period-thicknesses remain structure stable. Excellent swift-heavy-ions irradiation resistance also appeared in the multilayer with period-thickness of 3 nm. No elongation was observed because the atoms generated due to gasification aggregated themselves around multilayers in their vicinity by Ostwald ripening.

3:20 PM  
Advanced Manufacturing of Nanostructured Ferritic Steels with Enhanced Irradiation Performance for Nuclear Applications: Somayeh Pasebani1; Indrajit Charit1; 1University of Idaho
    Nanostructured ferritic steel with composition of Fe-14Cr-1Ti-0.3Mo-0.5La2O3 (wt%) was developed via mechanical alloying and spark plasma sintering. The sintered samples were irradiated by Fe2+ ions up to 400 dpa. Microstructural and mechanical characteristics of the irradiated samples were studied using different microscopy techniques and nanoindentation, respectively. The microstructure and hardness of the irradiated samples were evaluated and compared with those of the un-irradiated sample. The overall grain structure and dislocation configuration did not exhibit any significant changes from thermal treatments to 500 C or ion irradiation. No clear evidence of dislocation loops or void swelling was found in the irradiated samples. The dislocation density constantly increased with increasing irradiation dose causing hardening across the entire irradiation damage depth. The high number density of the La–Ti–O- enriched particles could play a significant role in stabilizing the dislocation configurations by acting as sites for defect recombination.

3:40 PM Break

4:00 PM  
Computational Simulation of Threshold Displacement Energy of GaAs: Nanjun Chen1; Sean Gray1; Fei Gao1; Danhong Huang2; David A Cardimona2; 1University of Michigan; 2US Air force Research Laboratory
    GaAs has received considerable attention due to its potential usefulness in high-power space-energy systems and special space-probe applications, but it may be limited on interplanetary missions due to space radiation damage. We have used molecular dynamic simulation with bond-order potential to study the threshold displacement energy of GaAs along the 3600 directions for for Ga and As, which are confined in four unit stereographic triangles. Several defect configurations together with the separation distances especially in low index directions were also identified. For both Ga and As, the minimum Ed was found to be 10 eV, but the maxima reached at 25 eV for Ga and 30 eV for As, respectively. When all the 3600 directions were taken into consideration, the average threshold displacement energies were 13.75 eV (for Ga) and 14.3 eV (for As) which were in good agreement with those reported in the experiments.

4:20 PM  
Thermal Conductivity of Uranium: Eric Tea1; Celine Hin1; 1Virginia Tech
    Uranium and its alloys, such as U-Zr systems, are being investigated for their use as metallic fuels for fast reactors. Their safety and efficiency depend notably on their swelling characteristics and thermal conductivity. However, modeling fundamental properties of actinides is challenging due to the sensitivity on the partial occupation of the 5f-orbitals. This has been illustrated by recent debates on the validity of different implementations of Density Functional Theory (all electron versus pseudopotential) and different exchange and correlation approximations (LDA, GGA, DFT+U) for Uranium. Moreover, the validation of modelling is not straightforward due to the scarcity of transport experiments and the difficulty in obtaining a Uranium single crystal. This particularly impacts thermodynamic, mechanical and thermal properties. We report the development of a Projector Augmented Wave (PAW) peudopotential used for the calculation of cohesive energies, volume per atom, bulk modulus, magnetic moments, and thermal conductivity of uranium and its alloys.

4:40 PM  
First-principles Study of Nano-layered Ceramic Coatings for U-Mo/Al Dispersion Fuel: Zhi-Gang Mei1; Sumit Bhattacharya2; Abdellatif Yacout1; 1Argonne National Laboratory; 2Northwestern University
    U-Mo based dispersion fuels are currently investigated as low enriched uranium fuels for high-performance research reactors. To reduce the formation of anomalous interaction layers in U-Mo/Al dispersion fuels, several materials have been deposited on U-Mo particles as diffusion barriers. Recently, ZrN coating has been successfully deposited on U-Mo particles using atomic layer deposition at Argonne National Laboratory. Experiment also shows that additional Al2O3 layer can improve the bonding between ZrN and U-Mo. So far, there is no study of the interfaces formed between diffusion barriers and fuel particles. To this end, we investigate the interfaces of ZrN/U and ZrN/Al2O3 and their effects on radiation-induced defects using first-principles calculations. The stable atomic structures of ZrN/U and ZrN/Al2O3 interfaces are predicted through the calculated interfacial energy. The effect of the interfaces on the migration of fission gas and defects are systematically investigated to understand the impact of nano-scaled coating on radiation tolerance.