Calculation of the substitutional fraction of ion-implanted He in an Fe target

Ion-implantation is a useful technique to study irradiation damage in nuclear materials. To study He effects in nuclear fusion conditions, He is co-implanted with damage ions to reproduce the correct He/dpa ratios in the desired or available depth range. However, the short-term fate of these He ions, i.e over the time scales of their own collisional phase, has not been yet unequivocally established. Here we present an atomistic study of the short-term evolution of He implantation in an Fe substrate to approximate the conditions encountered in dual ion-implantation studies in ferritic materials. Specifically, we calculate the fraction of He atoms that end up in substitutional sites shortly after implantation, i.e. before they contribute to long-term miscrostructural evolution. We find that fractions of at most 3% should be expected for most implantation studies. In addition, we carry out an exhaustive calculation of interstitial He migration energy barriers in the vicinity of matrix vacancies and find that they vary from approximately 20 to 60 meV depending on the separation and orientation of the He-vacancy pair.Comment: 7 pages, 6 figures, 2 table

PVP2009-77360 PROPOSAL OF RATIONAL DETERMINATION OF FRACTURE TOUGHNESS LOWER-BOUND CURVES BY MASTER CURVE APPROACH

ABSTRACT The Master Curve gives the relation between the median of fracture toughness and temperature in ductile-brittle transition temperature region. The procedure to determine the Master Curve is provided in the current ASTM E1921 standard. Considering the substitution of the alternative lower-bound curves based on the Master Curve approach for the recursive KIc curves in the present codes, the statistical characteristic should be well incorporated into the determination of the lower-bound curves. The appendix in the ASTM standard provides the procedure to derive the lower-bound curves, however, it seems to be addressed without sufficient consideration on statistical reliability. In this study, we proposed a rational determination method of fracture toughness lower-bound curves based on the Master Curve approach. The method took account of the effect of sample size in the determination of the tolerance bound curve. The adequacy of the proposed method was then verified by comparing with a fracture toughness database for RPV steels. The method allows the application of the Master Curve using fewer specimens, which can coexist with the present surveillance program. INTRODUCTION The Master Curve gives the relation between the median of fracture toughness and temperature in ductile-brittle transition temperature region. The Master Curve method rests on several assumptions. One of the key assumptions of the Master Curve is that the scatter in fracture toughness is captured by the weakest link statistics with a three-parameter Weibull distribution with a slope of 4. The statistical mode

Influence of free surfaces on microstructure evolution of radiation damage in Fe from molecular dynamics and object kinetic Monte Carlo calculations

The influence of surfaces on the evolution of damage of irradiated Fe is studied using object kinetic Monte Carlo with input from molecular dynamics simulations and ab initio calculations. Two effects are analysed: the influence of traps and the initial distribution of damage in the cascade. These simulations show that for a trap concentration of around 100 appm, there are no significant differences between defect concentrations in bulk and thin films. However, the initial distribution of defects plays an important role not only on total defect concentration but also on defect type, for the model used in this study. Damage produced by a 100 keV Fe ion impinging a Fe thin film. Blue (dark) spheres are self-interstitials, red (light) spheres are vacancies.The research leading to these results is partly funded by the European Atomic Energy Community’s (Euratom) Seventh Framework Programme FP7/2007–2013 under grant agreement no. 604862 (MatISSE project) and in the framework of the EERA (European Energy Research Alliance) Joint Programme on Nuclear Materials. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014–2018 under grant agreement no. 633053

Formation energy of vacancies in FeCr alloys: Dependence on Cr concentration

A modified version of the concentration-dependent model (CDM) potential (A. Caro et al., Phys. Rev. Lett. 95 (2005) 075702) [1] has been developed to study defects in Fe–Cr for different Crconcentrations. A comparison between this new potential and DFT results for a variety of point defect configurations is performed in order to test its reliability for radiation damage studies. The effect of Crconcentration on the vacancyformationenergy in Fe–Cr alloys is analyzed in detail. This study shows a linear dependence of the vacancyformationenergy on Crconcentration for values above 6% of Cr. However, the formationenergy deviates from the linear interpolation in the region below 6% Crconcentration. In order to understand this behavior, the influence of the relative positions between Cr atoms and vacant sites on the vacancyformationenergy has been studied

Roughness Encoding in Human and Biomimetic Artificial Touch: Spatiotemporal Frequency Modulation and Structural Anisotropy of Fingerprints

The influence of fingerprints and their curvature in tactile sensing performance is investigated by comparative analysis of different design parameters in a biomimetic artificial fingertip, having straight or curved fingerprints. The strength in the encoding of the principal spatial period of ridged tactile stimuli (gratings) is evaluated by indenting and sliding the surfaces at controlled normal contact force and tangential sliding velocity, as a function of fingertip rotation along the indentation axis. Curved fingerprints guaranteed higher directional isotropy than straight fingerprints in the encoding of the principal frequency resulting from the ratio between the sliding velocity and the spatial periodicity of the grating. In parallel, human microneurography experiments were performed and a selection of results is included in this work in order to support the significance of the biorobotic study with the artificial tactile system

The Effects of Cyclodextrins on the Reduction of Ninhydrin with N-Alky1-1, 4-dihydronicotinamides

The effects of adding various cyclodextrins (α-,β- and γ-cyclodextrin) on the redox reaction between N-alky1-1, 4-dihydronicotinamide (hydride ion donnor) and ninhydrin (hydride ion acceptor) in aqueous solutions were studied kinetically. These reactions proceed through the hydride ion donnor-acceptor complex (CT complex) formation without cyclodextrin (CD). The presence of CD especially affects the reduction with N-benzy1-1,4-dihydronicotinamide (BNAH). β-CD is most effective for decreasing the reduction rate in three CDs. β-CD inhibited the formation of the CT complex by including BNAH molecule, which caused a decrease in the reaction rate. β-CD also completely inhibited the hydration of BNAH. γ-CD also included BNAH, however, it had little effect on the reduction rate constant. α-CD had no effect on both the reduction and the hydration. These inhibition behaviors were caused by an inclusion complex formation with CD