Neutron Atypical Effects and the Influence on the Radiation Response of Metallic Alloys at Ultra-High Damage Levels

Cladding materials in next-generation fast reactors are expected to reach damage levels of 500 displacements per atom (dpa) or greater during the lifetime of the fuel. Austenitic stainless steel cladding showed excessive void swelling that limited the lifetime of the fuel, ultimately reducing the fuel economy. Ferritic-martensitic steels have been shown to be more resistant to void swelling than their austenitic counterparts, swelling at a rate of 0.2%/dpa compared to 1%/dpa in the steady-state swelling regime. With few fast flux facilities capable of achieving 500 displacements per atom within a few decades, ion irradiation has been selected as a surrogate for neutron irradiation to quickly screen fuel cladding candidates. Ion irradiation, however, differs intrinsically from neutron irradiation and several of these differences dramatically impact the microstructural development under irradiation. Before engaging in ultra-high damage level irradiations, an understanding of these neutron atypical phenomena is required. In this work, three of the neutron atypical effects that influence the radiation response most strongly are investigated: defect imbalance, temporal damage rate gradients, and compositional modification by Coulomb drag induced via ion bombardment. Although the defect imbalance effect is intrinsic to ion irradiation, using a static defocused beam and a specialized filtering system can reduce the effect that the latter two neutron atypical phenomena have on the microstructural development. At low damage levels (<100 dpa), structural engineering to produce fine-grained microstructures resulted superior radiation resistance. There are no studies that have examined the response at high damage levels in order to determine the stability of the microstructure. A ferritic/martensitic alloy, T91, and its variant subject to equal channel angular extrusion are irradiated to 1000 dpa and the radiation response of microstructures compared in order to evaluate the stability of features produced by severe deformation at damage levels expected in next-generation fast reactors

Animal Performance and Diet Quality While Grazing Corn Residue

Grazing cattle on corn residue as a winter feed source has become an integral part of many Nebraska producers’ management plans. Utilizing corn residues extends the grazing season and is often more economical than grazing winter range or dry lot situations. Corn residue is high in OM and NDF, moderate in digestibility, and low in CP. Cattle grazing corn residues may need to be supplemented with a protein source to meet requirements. The development and application of DNA technology to create new corn hybrids has improved yields with fewer inputs, leading to a continued low cost food supply for consumers. Previous research has demonstrated the safety of transgenic corn, silage, and corn residue as livestock feed sources. In all trials, transgenic corn is nutritionally similar to non-transgenic corn. In the current trial, four treatments were applied to a 53 ha center pivot irrigated field of corn. Treatments included a control, light grazing (2.5 AUM/ha), heavy grazing (4.9 AUM/ha), and baling, Samples were collected from all treatment paddocks before and after grazing and analyzed for DM, OM, CP, NDF, IVDMD, and in vitro organic matter digestibility (IVOMD). Leaf and husk material were consumed in the greatest amount on both grazing treatments. In general, leaf and husk residue had greater CP compared to cob and stem residue. Husk and cob residue had greater NDF content than leaf and stem residue. Digestibility of the residues ranged from 44 to 59%.. Undegradable intake protein digestibility of corn residue is low. Husk and leaf residue UIP digestibility was approximately 23%. Leaf and husk residue from several transgenic hybrids grown in western Nebraska had greater CP compared to stem and cob residue. Cobs had greater NDF content compared to leaf, husk, and stem residue. Husk and leaf residue from all hybrids had greater digestibility compared to stem and cob residue. A relationship between husk and leaf yield per bushel of grain produced per hybrid was not observed in this trial

Mechanical Response of He- Implanted Amorphous SiOC/ Crystalline Fe Nanolaminates

This study investigates the microstructural evolution and mechanical response of sputter-deposited amorphous silicon oxycarbide (SiOC)/crystalline Fe nanolaminates, a single layer SiOC film, and a single layer Fe film subjected to ion implantation at room temperature to obtain a maximum He concentration of 5 at. %. X-ray diffraction and transmission electron microscopy indicated no evidence of implantation-induced phase transformation or layer breakdown in the nanolaminates. Implantation resulted in the formation of He bubbles and an increase in the average size of the Fe grains in the individual Fe layers of the nanolaminates and the single layer Fe film, but the bubble density and grain size were found to be smaller in the former. By reducing the thicknesses of individual layers in the nanolaminates, bubble density and grain size were further decreased. No He bubbles were observed in the SiOC layers of the nanolaminates and the single layer SiOC film. Nanoindentation and scanning probe microscopy revealed an increase in the hardness of both single layer SiOC and Fe films after implantation. For the nanolaminates, changes in hardness were found to depend on the thicknesses of the individual layers, where reducing the layer thickness to 14 nm resulted in mitigation of implantation-induced hardening

Resistance to Helium Bubble Formation in Amorphous SiOC/Crystalline Fe Nanocomposite

The management of radiation defects and insoluble He atoms represent key challenges for structural materials in existing fission reactors and advanced reactor systems. To examine how crystalline/amorphous interface, together with the amorphous constituents affects radiation tolerance and He management, we studied helium bubble formation in helium ion implanted amorphous silicon oxycarbide (SiOC) and crystalline Fe composites by transmission electron microscopy (TEM). The SiOC/Fe composites were grown via magnetron sputtering with controlled length scale on a surface oxidized Si (100) substrate. These composites were subjected to 50 keV He+ implantation with ion doses chosen to produce a 5 at% peak He concentration. TEM characterization shows no sign of helium bubbles in SiOC layers nor an indication of secondary phase formation after irradiation. Compared to pure Fe films, helium bubble density in Fe layers of SiOC/Fe composite is less and it decreases as the amorphous/crystalline SiOC/Fe interface density increases. Our findings suggest that the crystalline/amorphous interface can help to mitigate helium defect generated during implantation, and therefore enhance the resistance to helium bubble formation

Mechanical Response of He- Implanted Amorphous SiOC/ Crystalline Fe Nanolaminates

This study investigates the microstructural evolution and mechanical response of sputter-deposited amorphous silicon oxycarbide (SiOC)/crystalline Fe nanolaminates, a single layer SiOC film, and a single layer Fe film subjected to ion implantation at room temperature to obtain a maximum He concentration of 5 at. %. X-ray diffraction and transmission electron microscopy indicated no evidence of implantation-induced phase transformation or layer breakdown in the nanolaminates. Implantation resulted in the formation of He bubbles and an increase in the average size of the Fe grains in the individual Fe layers of the nanolaminates and the single layer Fe film, but the bubble density and grain size were found to be smaller in the former. By reducing the thicknesses of individual layers in the nanolaminates, bubble density and grain size were further decreased. No He bubbles were observed in the SiOC layers of the nanolaminates and the single layer SiOC film. Nanoindentation and scanning probe microscopy revealed an increase in the hardness of both single layer SiOC and Fe films after implantation. For the nanolaminates, changes in hardness were found to depend on the thicknesses of the individual layers, where reducing the layer thickness to 14 nm resulted in mitigation of implantation-induced hardening

Corn residue stocking rate affects cattle performance but not subsequent grain yield

This study investigated effects of stocking rate on cattle performance, quality and quantity of corn residue, and impact of residue removal on grain yield for 5 yr at the University of Nebraska – Lincoln West Central Water Resources Field Laboratory near Brule, NE. Four removal treatments—1) no removal (control), 2) grazing at 2.5 animal unit month (AUM)/ ha, 3) grazing at 5.0 AUM/ha, and 4) baling—were applied to a center pivot–irrigated corn field (53 ha). The field was divided into eight 6.6-ha paddocks to which replicated treatments were assigned. Samples of residue were collected in October and March (before and after residue removal) using ten 0.5-m2 quadrats per treatment replication. Residue was separated into 5 plant parts—stem, cob, leaf, husk, and grain—and analyzed for nutrient content. Esophageally fistulated cattle were used to measure diet quality. Cattle assigned to the 2.5 AUM/ha stocking rate treatment gained more BW (P \u3c 0.01) and BCS (P \u3c 0.01) than cattle assigned to the 5.0 AUM/ha treatment. Leaf contained the most (P \u3c 0.01) CP and husk had the greatest (P \u3c 0.01) in vitro OM disappearance (IVOMD) but the CP and IVOMD of individual plant parts did not differ (P \u3e 0.69) between sampling dates. Amount of total residue was reduced (P \u3c 0.05) by baling and both grazing treatments between October and March but was not different (P \u3e 0.05) in control paddocks between sampling dates. As a proportion of the total residue, stem increased (P \u3c 0.01) and husk decreased (P \u3c 0.01) between October and March. Diet CP content was similar (P = 0.10) between sampling dates for the 2 grazing treatments but IVOMD was greater after grazing in the 2.5 AUM/ha grazing treatment (P = 0.04). Subsequent grain yields were not different (P = 0.16) across all 4 residue removal treatments. At the proper stocking rate, corn residue grazing results in acceptable animal performance without negatively impacting subsequent corn grain production

Stable, Ductile and Strong Ultrafine HT-9 Steels via Large Strain Machining

Beyond the current commercial materials, refining the grain size is among the proposed strategies to manufacture resilient materials for industrial applications demanding high resistance to severe environments. Here, large strain machining (LSM) was used to manufacture nanostructured HT-9 steel with enhanced thermal stability, mechanical properties, and ductility. Nanocrystalline HT-9 steels with different aspect rations are achieved. In-situ transmission electron microscopy annealing experiments demonstrated that the nanocrystalline grains have excellent thermal stability up to 700 & DEG;C with no additional elemental segregation on the grain boundaries other than the initial carbides, attributing the thermal stability of the LSM materials to the low dislocation densities and strains in the final microstructure. Nano-indentation and micro-tensile testing performed on the LSM material pre- and post-annealing demonstrated the possibility of tuning the material's strength and ductility. The results expound on the possibility of manufacturing controlled nanocrystalline materials via a scalable and cost-effective method, albeit with additional fundamental understanding of the resultant morphology dependence on the LSM conditions

Effect of Heavy Ion Irradiation Dosage on the Hardness of SA508-IV Reactor Pressure Vessel Steel

Specimens of the SA508-IV reactor pressure vessel (RPV) steel, containing 3.26 wt. % Ni and just 0.041 wt. % Cu, were irradiated at 290 °C to different displacement per atom (dpa) with 3.5 MeV Fe ions (Fe2+). Microstructure observation and nano-indentation hardness measurements were carried out. The Continuous Stiffness Measurement (CSM) of nano-indentation was used to obtain the indentation depth profile of nano-hardness. The curves showed a maximum nano-hardness and a plateau damage near the surface of the irradiated samples, attributed to different hardening mechanisms. The Nix-Gao model was employed to analyze the nano-indentation test results. It was found that the curves of nano-hardness versus the reciprocal of indentation depth are bilinear. The nano-hardness value corresponding to the inflection point of the bilinear curve may be used as a parameter to describe the ion irradiation effect. The obvious entanglement of the dislocations was observed in the 30 dpa sample. The maximum nano-hardness values show a good linear relationship with the square root of the dpa