MICROSTRUCTURE AND MICROHARDNESS EVALUATION FOR NiCrAlY MATERIALS MANUFACTURED BY SPARK PLASMA SINTERING AND PLASMA SPRAYING

NiCrAlY deposited by different thermal spraying methods is commonly used as the bond coat material in thermal barrier coatings (TBCs). In the present study, two experimental coatings were deposited by hybrid water stabilized plasma (WSP-H) and radio frequency inductively coupled plasma (RF-ICP) using the same feedstock powder. Spark plasma sintering (SPS) was used to manufacture a compact NiCrAlY from the same feedstock powder as a reference material. Microstructure, internal oxidation, phase characterization and quantification of the mechanical behaviour in terms of microhardness were studied. The investigations clearly showed microstructural and mechanical differences between the NiCrAlY samples manufactured by different plasma technologies. The results confirmed that SPS and RF-ICP provide dense structures with no oxides due to the fabrication under protective atmosphere and similar mechanical properties. Thus, RF-ICP may be used for deposition of very dense coatings with microstructure and hardness comparable to compacted materials prepared by SPS

MECHANICAL PROPERTIES OF FORGED TUNGSTEN HEAVY ALLOYS

Tungsten heavy alloys are composite materials containing spherical tungsten particles embedded in binder matrix. Their excellent mechanical properties can be further improved by rotary forging. This paper aims to gain deeper understanding of the forging process by investigating the local elastic modulus, hardness, and residual stress of individual phases in W6Ni3Co pseudo-alloy. The resulting global properties of the composite material such as stress-strain behavior, fracture toughness and fatigue crack growth rate behavior are also studied. The results show that sintered and quenched material consists of highly textured matrix containing nearly perfect single crystal spheres of pure W. The rotary forging leads to significant lattice deformations destroying the texture and significantly increasing the hardness of both WNiCo matrix and W particles and making residual stresses in W particles anisotropic with increased compression along the longitudinal axis of the forged part

Analysis of security requirements for payment card industry and problems with their implementation

Rapid development of new technologies and their easy implementation introduces new risks that must be faced. This diploma thesis concentrates at payment card industry. Payment card industry come through significant development. Billions of dollar each year flow through these systems. New technologies like contactless cards, prepaid brand cards are emerging, ATM and payment terminal support new services and products. Merchant are looking for new opportunities. This situation brings along new threats and introduces new vulnerabilities. These are not necessarily new, only the whole environment got much more complicated and digger. Unfortunately the acting threats and vulnerabilities were not eliminated. Missing legislation measures and restricted enforceability are not sufficient to effectively fight against crime in this area. On the other hand sever organizations are aware of these threats and tries to face them. New security requirements were introduced for each separate subjects of payment card industry so that the risks are eliminated or their impact is reduced to an acceptable degree. Some of these requirements were already implemented and are in the scope of this work. The goal of this work is to explore these requirements. To find out what risks they are affecting and how effective they are. And in case of need help to implement the appropriate security measure. This work is practically oriented and can help responsible persons to ensure compliance with the requirements and face all effecting threats

Systémy detekce průniků

Vzhledem k rostoucímu trendu využívání Internetu, nejen k získávání dat a informací, ale i jejich zneužití, roste význam jednotlivých prvků zabezpečení. Důležitou součást obrany informačního systému tvoří Systémy detekce průniku (IDS - Intrusion Detection System), které v reálném čase sledují provoz na síti a jsou schopny vyhodnotit a odfiltrovat nežádoucí komunikaci. Nasazení IDS je komplexní proces, který má dopad na celou organizaci a proto je třeba důkladně zvážit všechna jeho specifika a rozhodnout, zda-li bude IDS skutečně přínosem

On tungsten spraying using inductively coupled plasma system - First results

Thanks to its unique properties such as high melting point and density, tungsten and tungsten-based alloys are commonly used in a wide range of applications. Among others, these materials are promising candidates for the plasma facing components in the future fusion reactors. One of considered ways of production of these parts is plasma spraying. There are however several limitations for conventional gas stabilized torches, mainly in plasma enthalpy (i.e. the ability to efficiently melt tungsten particles in considerable feed rates) and susceptibility of tungsten to oxidation (which complicates spraying in oxidizing open-air atmosphere). The radio frequency inductively coupled plasma torch (RF-ICP) is a unique system which can potentially overcome both these problems and can be used for efficient tungsten spraying. The tungsten powder, which can be finer than the one used for the conventional systems, is fed axially into the hot plasma core, both factors lead to a more efficient melting of the particles. The deposition is performed in a chamber with controlled atmosphere of inert gas or decreased pressure, the oxidation is therefore suppressed. In this first study carried out with the newly commissioned RF-ICP system TekSpray 15 (Tekna), samples of tungsten coatings on graphite substrates were prepared. The X-ray diffraction and SEM images of the free surfaces and cross-sections were obtained, documenting high purity of the deposits and appropriate flattening of the splats leading to a dense coating microstructure. The effect of substrate preheating on the microstructure, porosity and hardness was also studied

Individual-level specialisation and interspecific resource partitioning in bees revealed by pollen DNA metabarcoding

It is increasingly recognised that intraspecific variation in traits, such as morphology, behaviour, or diet is both ubiquitous and ecologically important. While many species of predators and herbivores are known to display high levels of between-individual diet variation, there is a lack of studies on pollinators. It is important to fill in this gap because individual-level specialisation of flower-visiting insects is expected to affect their efficiency as pollinators with consequences for plant reproduction. Accordingly, the aim of our study was to quantify the level of individual-level specialisation and foraging preferences, as well as interspecific resource partitioning, in three co-occurring species of bees of the genus Ceratina (Hymenoptera: Apidae: Xylocopinae), C. chalybea, C. nigrolabiata, and C. cucurbitina. We conducted a field experiment where we provided artificial nesting opportunities for the bees and combined a short-term mark-recapture study with the dissection of the bees’ nests to obtain repeated samples from individual foraging females and complete pollen provisions from their nests. We used DNA metabarcoding based on the ITS2 locus to identify the composition of the pollen samples. We found that the composition of pollen carried on the bodies of female bees and stored in the brood provisions in their nests significantly differed among the three co-occurring species. At the intraspecific level, individual females consistently differed in their level of specialisation and in the composition of pollen carried on their bodies and stored in their nests. We also demonstrate that higher generalisation at the species level stemmed from larger among-individual variation in diets, as observed in other types of consumers, such as predators. Our study thus reveals how specialisation and foraging preferences of bees change from the scale of individual foraging bouts to complete pollen provisions accumulated in their nests over many days. Such a multi-scale view of foraging behaviour is necessary to improve our understanding of the functioning of plant-flower visitor communities

Properties of Mechanically Alloyed W-Ti Materials with Dual Phase Particle Dispersion

W alloys are currently widely studied materials for their potential application in future fusion reactors. In the presented study, we report on the preparation and properties of mechanically alloyed W-Ti powders compacted by pulsed electric current sintering. Four different powder compositions of W-(3%–7%)Ti with Hf or HfC were prepared. The alloys’ structure contains only high-melting-point phases, namely the W-Ti matrix, complex carbide (Ti,W,Hf)C and HfO2 particle dispersion; Ti in the form of a separate phase is not present. The bending strength of the alloys depends on the amount of Ti added. The addition of 3 wt. % Ti led to an increase whereas 7 wt. % Ti led to a major decrease in strength when compared to unalloyed tungsten sintered at similar conditions. The addition of Ti significantly lowered the room-temperature thermal conductivity of all prepared materials. However, unlike pure tungsten, the conductivity of the prepared alloys increased with the temperature. Thus, the thermal conductivity of the alloys at 1300 °C approached the value of the unalloyed tungsten

Úloha laserového strukturování při zlepšování adheze plazmově stříkaných wolframových povlaků

Plasma sprayed W-based coatings have thepotential application as joining interlayers for the plasma-facing components of future fusion reactors. Particularly inthe form of tungsten-steel functionally graded materials(FGMs), they would reduce the stress concentrationbetween the W-based plasma-facing armor and steel-basedconstruction. For mechanical integrity, good adhesion isessential. For this, conventional grit blasting treatment ofthe substrate may not be sufficient. Therefore, alternativetreatments capable of reaching significantly higher rough-ness without damaging the substrate are sought. In thisstudy, the effects of laser texturing on the adhesion ofplasma sprayed W and W-steel FGMs on W and steelsubstrates are investigated. A variety of surface profileswere achieved by controlled laser ablation in several typesof patterns. Their geometric features were systematicallyvaried and measured, and the extent of their filling by thecoating material was evaluated. On the most promisingpatterns, coating adhesion tests were performed in shearloading mode and the best performing patterns wereidentified. Significant improvement over grit-blasted sur-face was obtained on patterned surfaces with a higheffective contact area, promoting mechanical interlocking.On steel substrates, generally higher adhesion wasobserved, surpassing already the coating cohesive strength; this is attributed to a combination of mechanical inter-locking and metallurgical bonding.Plazmově stříkané povlaky na bázi W mají potenciální použití jako spojovací mezivrstvy pro komponenty budoucích fúzních reaktorů v kontaktu s plazmatem. Zejména ve formě funkčně odstupňovaných materiálů (FGM) wolfram-ocel by snížily koncentraci napětí mezi štítem ve styku s plazmatem na bázi W a konstrukcí na bázi oceli. Pro mechanickou integritu je dobrá přilnavost nezbytná. K tomu nemusí být dostatečné běžné otryskávání substrátu. Proto se hledají alternativní úpravy schopné dosáhnout výrazně vyšší drsnosti bez poškození substrátu. V této studii jsou zkoumány účinky laserového texturování na adhezi plazmově stříkaných W a FGM W-ocel na W a oceli. Řadu povrchových profilů bylo dosaženo řízenou laserovou ablací v několika typech vzorů. Jejich geometrické vlastnosti byly systematicky měněny a měřeny a byl hodnocen rozsah jejich plnění povlakovým materiálem. Na nejslibnějších texturách byly provedeny testy přilnavosti povlaku v režimu střihového zatížení a byly identifikovány nejlépe vyhovující struktury. Významné zlepšení oproti povrchu s otryskaným povrchem bylo dosaženo na strukturovaných površích s vysoce účinnou kontaktní plochou, která podporuje mechanické zaseknutí. Na ocelových substrátech byla obecně pozorována vyšší adheze, která již překonala soudržnost povlaku; toto je připisováno kombinaci mechanického vzájemného zaseknutí a metalurgického spojení