Influence of the stress field due to pressurized nanometric He bubbles on the mobility of an edge dislocation in iron

Voids and He bubbles are strong obstacles to dislocation, which induce hardening and loss of ductility. In Fe, molecular dynamics simulation is used to investigate the basic mechanisms of the interaction between a moving edge dislocation and a void or He bubble, as a function of its He content, temperature, interatomic potentials and interaction geometry. Different interatomic potentials for Fe-Fe and Fe-He interactions are used. It appears that temperature eases the dislocation release, due to the increased mobility of the screw segments appearing on the dislocation line upon bowing from the void or He bubble. The mobility includes the cross-slipping of these segments, which leads to the formation of a jog. It appears that the He bubble induces an inhomogeneous stress field in its surroundings, which strongly influences the dislocation passage depending on the geometry of the interaction

Aluminum partitioning during phase separation in Fe-20%Cr-6%Al

Phase separation in a commercial Fe–20 wt.% Cr–6%Al oxide dispersion-strengthened PM 2000 steel has been characterized with a local-electrode atom probe after isothermal aging at 708 Kand 748 Kfor times up to 3,600 h. A progressing decrease in the Al content of the Cr-rich a0 phase was observed with time at both aging temperatures. The Al partitioning trend was consistent with theoretical calculations. However, the experimentally observed Al partitioning factor was significantly lower than the predicted equilibrium value. A *10 nm diameter, roughly spherical, Al- and Ti-enriched b0 Fe(AlTi) phase was also observedSpanish Ministerio de Educación y Ciencia in the form of a Coordinate Project in the Energy Area of Plan Nacional 2006 (ENE2006-15170-C02). Research at the Oak Ridge National Laboratory SHaRE User Facility was sponsored by Basic Energy Sciences, U.S. Department of Energy. PM 2000™ is a trademark of Plansee SEPeer reviewe

Microstructural development under irradiation in European ODS ferritic/martensitic steels

Oxide dispersion strengthened steels based on the ferritic/martensitic steel EUROFER97 are promising candidates for a fusion reactor because of their improved high temperature mechanical properties and their potential higher radiation resistance relative to the base material. Several EUROFER97 based ODS F/M steels are investigated in this study. There are the Plansee ODS steels containing 0.3 wt% yttria, and the CRPP ODS steels, whose production route is described in detail. The reinforcing particles represent 0.3-0.5% weight and are composed of yttria. The effect of 0.3 wt% Ti addition is studied. ODS steel samples have been irradiated with 590 MeV protons to 0.3 and 1.0 dpa at room temperature and 350 degrees C. Microstructure is investigated by transmission electron microscopy and mechanical properties are assessed by tensile and Charpy tests. While the Plansee ODS presents a ferritic structure, the CRPP ODS material presents a tempered martensitic microstructure and a uniform distribution of the yttria particles. Both materials provide a yield stress higher than the base material, but with reduced elongation and brittle behaviour. Ti additions improve elongation at high temperatures. After irradiation, mechanical properties of the material are only slightly altered with an increase in the yield strength, but without significant decrease in the total elongation, relative to the base material. Samples irradiated at room temperature present radiation induced defects in the form of blacks dots with a size range from 2 to 3 nm, while after irradiation at 350 degrees C irradiation induced a(0)(100){100} dislocation loops are clearly visible along with nanocavities. The dispersed yttria particles with an average size of 6-8 nm are found to be stable for all irradiation conditions. The density of the defects and the dispersoid are measured and found to be about 2.3 x 10(22) m(-3) and 6.2 x 10(22) m(-3), respectively. The weak impact of irradiation on mechanical properties of ODS F/M steel is thus explained by a lower density of irradiation induced defects relative to the density of reinforcing particles. (c) 2006 Elsevier B.V. All rights reserved

Effects of dietary supplementation with synthetic vitamin D-3 and 25-hydroxycholecalciferol on blood calcium and phosphate levels and performance in laying hens

We investigated the effects of different dietary vitamin D regimen on selected blood parameters in laying hens. Supplementation with vitamin D-3 only was compared with a combination of vitamin D-3 and its metabolite 25-hydroxy-cholecalciferol (25(OH)D-3). Blood concentrations of total calcium, phosphate and 25 (OH)D-3 were determined. Four thousand one-day-old LSL chicks were split in two treatment groups and distributed to eight pens. The control group was given a commercial animal diet containing 2800 IU synthetic vitamin D-3 in the starter feed and 2000 IU synthetic vitamin D-3 in the pullet feed. The experimental group was fed the same commercial diet in which half the synthetic vitamin D-3 content had been substituted with 25(OH)D-3 (Hy center dot D (R)). At 18 weeks of age, pullets were transferred to the layer house. At the ages of 11, 18 and 34 weeks, between 120 and 160 blood samples were collected from both the control and the experimental groups, respectively. The experimental group had higher levels of 25 (OH)D-3 than the control group at all three ages. Serum calcium levels did not differ between the treatment groups at any age. With the onset of laying, calcium levels rose significantly. Whereas blood serum concentration at 18 weeks was 3 mmol/L in both treatment groups, it increased to 8.32 mmol/L in the control group and to 8.66 mmol/L in the experimental group at week 34. At weeks 11 and 34, phosphate was significantly lower in the experimental group. In conclusion, HyD (R) significantly affected serum phosphate and 25(OH)D-3 levels. No effects of (25(OH)D-3 supplementation on performance, shell quality and fractures of keelbones were found