Atomic structure of grain boundaries in iron modeled using the atomic density function

A model based on the continuous atomic density function (ADF) approach is applied to predict the atomic structure of grain boundaries (GBs) in iron. Symmetrical [100] and [110] tilt GBs in bcc iron are modeled with the ADF method and relaxed afterwards in molecular dynamics (MD) simulations. The shape of the GB energy curve obtained in the ADF model reproduces well the peculiarities of the angles of 70.53 deg. [$\Sigma$ 3(112)] and 129.52 deg. [$\Sigma$ 11(332)] for [110] tilt GBs. The results of MD relaxation with an embedded-atom method potential for iron confirm that the atomic GB configurations obtained in ADF modeling are very close to equilibrium ones. The developed model provides well-localized atomic positions for GBs of various geometries.Comment: 8 pages, 8 figures, revised versio

Relation between the Ultrasonic Attenuation and the Porosity of a RTM Composite Plate

AbstractWe propose a comparative study of X-ray tomography and ultrasonic reflection methods, for determining the porosity of a composite plate realized in LOMC with an industrial process. We measure the attenuation of ultrasound propagating in the thickness by using 10MHz plane transducer in pulse-echo mode. Comparing these results to the 2D porosity tomographic map allows establishing a relation between attenuation and porosity. A C-scan picture of the plate given by the echoes reflected by the rear surface also provides a local information on the attenuation. Furthermore, we propose a method for the mapping of the reflecting sources as the included bubbles and the interfaces resin/fibers

Перераспределение примесных и легирующих элементов в стали корпуса реактора ВВЭР-440 под действием эксплуатационных факторов

Материал, вырезанный из темплетов сварного металла ВВЕР-440, был исследован при помощи APFIM в трех состояниях: облученном, облученном и отожженном, облученном, отожженном и повторно облученном. Были получены данные по химическому составу ферритной матрицы, а также 3D изображения структурных особенностей (кластеров, мелких карбидов и т.д.). Эксперименты показали формирование мелких (примерно 2 нм) кластеров, обогащенных Cu, Si, Ni, Mn, P в процессе облучения. распад этих кластеров происходит в процессе отжига с формированием новых, более крупных (примерно 5 нм) кластеров из чистой Сu с последующим формированием Р-обогащенных зон на второй стадии облучения с незначительными изменениями в более крупных Cu-кластерных структурах в рамках изучаемого интервала флюенса повторного облучения. Предполагается, что Р-обогащенные зоны играют важную роль в упрочнении ферритной матрицы в процессе повторного облучения. Результаты демонстрируют существенное обеднение матрицы Р под облучением. Этот процесс может оказывать влияние на радиационно-обусловленную сегрегацию границ зерна Р в основном материале бака ВВЕР-440. Уровень сегрегации был вычислен при помощи модифицированной модели McLean. Результаты демонстрируют хорошее соответствие с экспериментальными данными, полученными оже-электронной спектроскопией.Матеріал, вирізаний з темплетів зварного металу ВВЕР-440, було досліджено за допомогою APFIM у трьох станах: опроміненому, опроміненому та відпаленому, опроміненому, відпаленому та вторинно опроміненому. Були отримані дані по хімічному складу ферітної матриці, а також 3D зображення структурних особливостей (кластерів, малих карбідів та інших). Експерименти показали формування малих (біля 2 нм) кластерів, збагачених Cu, Si, Ni, Mn, P під дією опромінення. розпад цих кластерів при відпалі з формуванням нових, більших за розміром (приблизно 5нм) кластерів практично із чистої Cu з подальшим формуванням Р-збагачених зон на другому етапі опромінення з незначними змінами в структурі крупніших Cu-кластерів у діапазоні флюенсу вторинного опромінення. Р-збагачені зони відіграють важливу роль у зміцненні ферітної матриці під дією повторного опромінення. Отримані результати демонструють суттєве збідніння матриці на Р під впливом опромінення. Цей процес може впливати на радіаційно-індуковану сегрегацію границь зерен Р в основному матеріалі баку реактора ВВЕР-440. Рівень сегрегації було розраховано за допомогою модифікованої моделі МсLеan. Отримані результати показують відповідність з експериментальними даними, отриманими оже- електронною спектроскопією.The material cut out of templets of WWER-440 weld metal was investigated by APFIM in three conditions: irradiated; irradiated and annealed; irradiated, annealed and re-irradiated. Data on the chemical content of ferrite matrix as well as 3D images of structural features (clusters, small carbides etc) were obtained. The experiments showed the formation of small (about 2 nm) clusters enriched by Cu, Si, Ni, Mn, P during irradiation, the decay of these clusters during annealing with the formation of new bigger (about 5 nm) almost pure Cu clusters and subsequent formation of P-enriched zones during the second stage of irradiation with no remarkable changes in the bigger Cu-clusters structure within the considered re-irradiation fluence range. The P-enriched zones are supposed to play an important role in the ferrite matrix hardening during re-irradiation. The results demonstrated the significant exhaustion of matrix by P under irradiation. This process could have an influence of radiation-induced grain boundary segregation of P in the base material of WWER-440 pressure vessel. The level of the segregation was calculated using the modified McLean model. The results showed the qualitative agreement with experimental data obtained by Auger electron spectroscopy

Lamb Wave Scattering from Rivets

For structures with large surface areas, a full integrity evaluation can be a time-consuming operation. Lamb wave techniques allow this evaluation to be performed with waves propagating along one dimension of the inspection area while the probing transducers are moved in the perpendicular dimension, giving information about the presence of flaws within the entire scanned area. For riveted structures the scattering of the Lamb waves from the rivets is often the dominant feature in the measured response, masking the more subtle effects of Lamb wave interactions with the flaws of interest [1]. In this paper we consider the scattering of lowest mode symmetric and antisymmetric Lamb waves from model rivets, and derive analytic expressions for the scattered fields. With solutions of this type the disruptive effects of the rivets can be “processed out” of measured data in order to expose the signals which are due to the flaws in the structure

Atomic scale investigation of silicon nanowires and nanoclusters

In this study, we have performed nanoscale characterization of Si-clusters and Si-nanowires with a laser-assisted tomographic atom probe. Intrinsic and p-type silicon nanowires (SiNWs) are elaborated by chemical vapor deposition method using gold as catalyst, silane as silicon precursor, and diborane as dopant reactant. The concentration and distribution of impurity (gold) and dopant (boron) in SiNW are investigated and discussed. Silicon nanoclusters are produced by thermal annealing of silicon-rich silicon oxide and silica multilayers. In this process, atom probe tomography (APT) provides accurate information on the silicon nanoparticles and the chemistry of the nanolayers

Efficient photogeneration of charge carriers in silicon nanowires with a radial doping gradient

From electrodeless time-resolved microwave conductivity measurements, the efficiency of charge carrier generation, their mobility, and decay kinetics on photo-excitation were studied in arrays of Si nanowires grown by the vapor-liquid-solid mechanism. A large enhancement in the magnitude of the photoconductance and charge carrier lifetime are found depending on the incorporation of impurities during the growth. They are explained by the internal electric field that builds up, due to a higher doped sidewalls, as revealed by detailed analysis of the nanowire morphology and chemical composition

Multiscale modelling for fusion and fission materials: the M4F project

The M4F project brings together the fusion and fission materials communities working on the prediction of radiation damage production and evolution and its effects on the mechanical behaviour of irradiated ferritic/martensitic (F/M) steels. It is a multidisciplinary project in which several different experimental and computational materials science tools are integrated to understand and model the complex phenomena associated with the formation and evolution of irradiation induced defects and their effects on the macroscopic behaviour of the target materials. In particular the project focuses on two specific aspects: (1) To develop physical understanding and predictive models of the origin and consequences of localised deformation under irradiation in F/M steels; (2) To develop good practices and possibly advance towards the definition of protocols for the use of ion irradiation as a tool to evaluate radiation effects on materials. Nineteen modelling codes across different scales are being used and developed and an experimental validation programme based on the examination of materials irradiated with neutrons and ions is being carried out. The project enters now its 4th year and is close to delivering high-quality results. This paper overviews the work performed so far within the project, highlighting its impact for fission and fusion materials science.This work has received funding from the Euratom research and training programme 2014-2018 under grant agreement No. 755039 (M4F project)