A model Fe-9%Cr oxide dispersion strengthened (ODS) steel was irradiated with protons or neutrons to a dose of 3 displacements per atom (dpa) at a temperature of 500°C, enabling a direct comparison of ion to neutron irradiation effects at otherwise fixed irradiation conditions. The irradiated microstructures were characterized using transmission electron microscopy and atom probe tomography including cluster analysis. Both proton and neutron irradiations produced a comparable void and dislocation loop microstructure. However, the irradiation response of the Ti-Y-O oxide nanoclusters varied. Oxides remained stable under proton irradiation, but exhibited dissolution and an increase in Y:Ti composition ratio under neutron irradiation. Both proton and neutron irradiation also induced varying extents of Si, Ni, and Mn clustering at existing oxide nanoclusters. Protons are able to reproduce the void and loop microstructure of neutron irradiation carried out to the same dose and temperature. However, since nanocluster evolution is controlled by both diffusion and ballistic impacts, protons are rendered unable to reproduce the nanocluster evolution of neutron irradiation at the same dose and temperature.
BACKGROUND: Delays in discharges affect both efficiency and timeliness of care; 2 measures of quality of inpatient care. OBJECTIVE: Describe number, length, and type of delays in hospital discharges. Characterize impact of delays on overall length of stay (LOS) and costs. DESIGN: Prospective observational cohort study. SETTING: Tertiary‐care children's hospital. PATIENTS: All children on 2 medical teams during August 2004. INTERVENTION: Two research assistants presented detailed data of patient care (from daily rounds) to 2 physicians who identified delays and classified the delay type. Discharge was identified as delayed if there was no medical reason for the patient to be in the hospital on a given day. MEASUREMENTS: Delays were classified using a validated and reliable instrument, the Delay Tool. LOS and costs were extracted from an administrative database. RESULTS: Two teams cared for 171 patients. Mean LOS and costs were 7.3 days (standard deviation [SD] 14.3) and $15,197 (SD 38,395), respectively: 22.8% of patients experienced at least 1 delay, accounting for 82 delay‐related hospital days (9% of total hospital days) and $170,000 in costs (8.9% of hospital costs); 42.3% of the delays resulted from physician behavior, 21.8% were related to discharge planning, 14.1% were related to consultation, and 12.8% were related to test scheduling. CONCLUSIONS: Almost one‐fourth of patients in this 1‐month period could have been discharged sooner than they were. Impact of delays on LOS and costs are substantial. Interventions will need to address variations in physician criteria for discharge, more efficient discharge planning, and timely scheduling of consultation and diagnostic testing. Journal of Hospital Medicine 2009;4:481–485. © 2009 Society of Hospital Medicine.
Thus far, a number of studies have investigated the irradiation evolution of oxide nanoparticles in b.c.c. Fe-Cr based oxide dispersion strengthened (ODS) alloys. But given the inconsistent experimental conditions, results have been widely variable and inconclusive. Crystal structure and chemistry changes differ from experiment to experiment, and the total nanoparticle volume fraction has been observed to both increase and decrease. Furthermore, there has not yet been a comprehensive review of the archival literature. In this paper, we summarize the existing studies on nanoparticle irradiation evolution. We note significant observations with respect to oxide nanoparticle crystallinity, composition, size, and number density. We discuss three possible contributing mechanisms for nanoparticle evolution: ballistic dissolution, Ostwald ripening, and irradiation-enhanced diffusion. Finally, we propose future directions to achieve a more comprehensive understanding of irradiation effects on oxide nanoparticles in ODS alloys.
The objective of this study is to evaluate the effect of irradiation on the strengthening mechanisms of a model Fe-9%Cr oxide dispersion strengthened steel. The alloy was irradiated with protons or neutrons to a dose of 3 displacements per atoms at 500°C. Nanoindentation was used to measure strengthening due to irradiation, with neutron irradiation causing a greater increase in yield strength than proton irradiation. The irradiated microstructures were characterized using transmission electron microscopy and atom probe tomography (APT). Cluster analysis reveals solute migration from the Y-Ti-O-rich nanoclusters to the surrounding matrix after both irradiations, though the effect is more pronounced in the neutron-irradiated specimen. Because the dissolved oxygen atoms occupy interstitial sites in the iron matrix, they contribute significantly to solid solution strengthening. The dispersed barrier hardening model relates microstructure evolution to the change in yield strength, but is only accurate if solid solution contributions to strengthening are considered simultaneously.
The objective of this study is to determine irradiation effects on the nanoindentation plastic zone morphology in a model Fe-9%Cr ODS alloy. Specimens are irradiated to 50 displacements per atom at 400°C with Fe ++ self-ions or to 3 dpa at 500°C with neutrons. The as-received specimen is also studied as a control. The nanoindentation plastic zone size is calculated using two approaches: (1) an analytical model based on the expanding spherical cavity analogy, and (2) finite element modeling (FEM). Plastic zones in all specimen conditions extend radially outward from the indenter, ~4-5 times the tip radius, indicative of fully plastic contact. Non-negligible plastic flow in the radial direction requires the experimentalist to consider the plastic zone morphology when nanoindenting ion-irradiated specimens; a single nanoindent may sample non-uniform irradiation damage, regardless of whether the indent is made top-down or in crosssection. Finally, true stress-strain curves are generated.
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