Materials for Fusion Applications

An overview of materials foreseen for use or already used in fusion devices is given. The operating conditions, material requirements and characteristics of candidate materials in several specific application segments are briefly reviewed. These include: construction materials, electrical insulation, permeation barriers and plasma facing components. Special attention will be paid to the latter and to the issues of plasma-material interaction, materials joining and fuctionally graded interlayers

Attributes Calculating for Prediction of Effects of Mutation on Protein Function

Tato bakalářská práce se pohybuje v oblasti bioinformatiky a zabývá se problematikou získávání atributů proteinů užitečných pro předpověď vlivu mutace na jejich funkci. Práce má především za cíl vytvořit uživatelsky přívětivou aplikaci, která pomocí specializovaných algoritmů jako je FoldX umožní snadno získat atributy mutací ze sekvence a struktury proteinů. Vyvinutá aplikace poskytuje standardizované rozhraní, které umožňuje rozšiřovat sadu výpočetních metod a získat tak rozmanité sady atributů z různých zdrojů. Tyto sady pak mohou být vstupem predikčních metod a mohou tak přispět ke zlepšení predikce škodlivosti mutace.This bachelor thesis deals with the bioinformatics techniques for the acquisition of attributes useful for prediction of mutation effects on the protein function. The work primarily aims to develop a user-friendly application for calculation of attributes of mutations from the protein sequence and structure. The developed application serves for integration of specialized tools such as FoldX. The standardized interface enables to implement additional computational tools and collect a diverse set of attributes from different sources. These attribute sets can then serve as an input for different prediction methods and help to improve predictions of mutation effects.

Influence of the Interface and the microstructural length scale on the grid indentation

The instrumented grid indentation of structurally heterogeneous materials using Oliver-Pharr method is frequently employed in order to characterize the properties of individual phases as this method is available in practically all commercial devices. However, when applying the statistical evaluation of results, the presence of boundary-affected results leads to the bias of the distribution, i.e. to the softer phase hardness and/or modulus overestimation together with the underestimation of harder phase values. The indentation in proximity of the interface cannot always be completely avoided – in the grid indentation the position of some indents can inevitably coincide with the phase boundary which can, moreover, be hidden below the indented surface. The aim of this paper is to shed some light on the effect of indentation in proximity of the interface on the statistical distribution of the grid indentation data. A case study on material composed of two phases with distinctly different hardness and Young’s modulus is presented. As an experimental material was chosen tungsten-copper composite. Samples were prepared using spark plasma sintering from pure metallic and ceramic powders which resulted in a sharp interface with abrupt change of material properties. The influence of depth of penetration and microstructural length scale on the measured hardness and/or modulus was integrated in the statistical analysis of the grid indentation data. The conditional probability of the indentation in the (affected) interfacial area was incorporated into the statistical distribution function based on the profile estimated by the finite element analysis and by the experimental study on the model material with the sharp interface. The unbiased (intrinsic) properties (including indentation size effect) were subsequently extracted from the experimental grid indentation data. Please click Additional Files below to see the full abstract

Influence of the Interface and the microstructural length scale on the grid indentation

The instrumented grid indentation of structurally heterogeneous materials using Oliver-Pharr method is frequently employed in order to characterize the properties of individual phases as this method is available in practically all commercial devices. However, when applying the statistical evaluation of results, the presence of boundary-affected results leads to the bias of the distribution, i.e. to the softer phase hardness and/or modulus overestimation together with the underestimation of harder phase values. The indentation in proximity of the interface cannot always be completely avoided – in the grid indentation the position of some indents can inevitably coincide with the phase boundary which can, moreover, be hidden below the indented surface. The aim of this paper is to shed some light on the effect of indentation in proximity of the interface on the statistical distribution of the grid indentation data. A case study on material composed of two phases with distinctly different hardness and Young’s modulus is presented. As an experimental material was chosen tungsten-copper composite. Samples were prepared using spark plasma sintering from pure metallic and ceramic powders which resulted in a sharp interface with abrupt change of material properties. The influence of depth of penetration and microstructural length scale on the measured hardness and/or modulus was integrated in the statistical analysis of the grid indentation data. The conditional probability of the indentation in the (affected) interfacial area was incorporated into the statistical distribution function based on the profile estimated by the finite element analysis and by the experimental study on the model material with the sharp interface. The unbiased (intrinsic) properties (including indentation size effect) were subsequently extracted from the experimental grid indentation data. Please click Additional Files below to see the full abstract

W-Cr solid solution: Comparison of alloying in SPS and by ball milling

Tungsten alloys currently represent prospective candidates to replace tungsten in the first wall applications in future fusion facilities. They are anticipated to suppress unfavorable mechanical properties of commercially pure tungsten and/or to gain advantages such as ability of self-passivation under accidental conditions. The self-passivating alloys are designed to minimize possible consequences related mainly to a LOCA (Loss of Coolant Accident) event with simultaneous air ingress into the reactor vessel. Please click Additional Files below to see the full abstract

Behavior of W-based materials in hot helium gas

Materials for the plasma facing components of future fusion reactors will be subjected to complex loading and various forms of interaction with low Z species (hydrogen isotopes and helium). The divertor components will be among the most intensely loaded, as they will have to transfer heat loads up to 10–20 MW/m2. Besides the plasma facing surface being irradiated by highly energetic deuterium, tritium and helium particles from the burning plasma, the opposite surface will be exposed to a cooling medium at elevated temperature. Helium- and water-based cooling systems are currently being considered. While tungsten is the prime candidate material for the plasma facing components, in the helium-cooled divertor designs, it is also foreseen as a structural material, together with ferritic–martensitic steels. The behavior of these materials in He atmosphere at elevated temperatures has been little studied thus far, and therefore is the subject of the current work. A number of W-based materials (pure tungsten and some of its alloys) prepared by powder metallurgy techniques was exposed to He atmosphere at 720 C and 500 kPa for 500 h. Morphological surface changes were observed by SEM, chemical and phase composition was analyzed by EDS and XRD, respectively. The internal microstructure was observed by a combination of SEM, FIB and TEM techniques. Mechanical properties were determined by instrumented indentation. Some alloys developed a thin oxide layer, in some cases new morphological features were observed, while some samples remained mostly intact. The observed changes are correlated with specific compositions and microstructures

On the Structural and Chemical Homogeneity of Spark Plasma Sintered Tungsten

Tungsten-based materials are the prime candidate plasma-facing materials for future fusion reactors, such as DEMO. Spark plasma sintering is a prospective fabrication technology with several advantageous features. The concurrent application of electric current, temperature and pressure enhances the sintering process, allowing for lower temperatures and shorter sintering times than traditional powder metallurgy processes. This in turn helps to avoid excessive grain growth and phase segregation in W-alloys. This study is focused on several factors that may influence the homogeneity of the sintered compacts—namely the diffusion of carbon from the graphite die, purity of the powder and sintering conditions. The following characteristics of spark plasma-sintered tungsten compacts were studied: composition (especially carbon and oxygen content), porosity, mechanical properties (hardness and fracture strength), and thermal diffusivity. The effects of the abovementioned processing factors were quantified, and local variations of selected properties were assessed

Tungsten-Steel Composites and FGMs Produced by Hot Pressing

Tungsten-steel composites and FGMs are being developed for potential application in plasma facing components of fusion devices. In this study, uniform composites and graded layers produced from tungsten and steel powders by hot pressing were investigated. Formation of dense composites with uniform distribution and good bonding of the phases was observed. A thin layer of intermetallic phase Fe7W6 formed at the interfaces. Thermal and mechanical properties of the composites in the as-produced and annealed state were characterized

ELECTRON BEAM REMELTING OF PLASMA SPRAYED ALUMINA COATINGS

Plasma sprayed alumina coatings find numerous applications in various fields, where they enhance the properties of the base material. Examples include thermal barriers, wear resistance, electrical insulation, and diffusion and corrosion barriers. A typical structure of plasma sprayed coatings, containing a multitude of voids and imperfectly bonded interfaces, gives them unique properties - particularly low thermal conductivity, high strain tolerance, etc. However, for certain applications such as permeation barriers or wear resistance, these voids may be detrimental.\nThis paper reports on the first experiments with remelting of plasma sprayed alumina coatings by electron beam technology, with the purpose of densifying the coatings and thereby eliminating the voids. Throughout the study, several parameters of the e-beam device were varied - beam current, traverse velocity and number of passes. The treated coatings were observed by light and electron microscopy and the thickness, structure and surface morphology of the remelted layer were determined and correlated with the process parameters. Based on the first series of experiments, the e-beam settings leading to dense and smooth remelted layer of sufficient thickness were obtained. In this layer, a change of phase composition and a marked increase in hardness were observed.\

Optimalizace vnášení prášku při plazmovém stříkání wolframu a mědi

Coatings of tungsten, copper and their composites can be used in various thermal management applications. For plasma spraying, injection of the feedstock powder is critical to achieve proper melting in the plasma jet and to produce coatings of desired properties. In this study, powder injection parameters were optimized while varying the injection location and carrier gas flow. Behavior of the particles in the plasma jet was observed using in-flight particle diagnostics; deposition efficiency as well as several coating properties were measured. Based on the results, the optimal injection conditions were selected, and composites and graded layers produced