Two aerospace superalloys, Inconel 718 and IMI 318, were machined with different grades of PVD (KC730 and KC732) and CVD (KC950) coated tools in order to evaluate their performance under various cutting conditions and to further investigate the effect of the machining conditions on surface finish and surface integrity of the work materials. A self-propelled rotary tool was also developed and used for machining under the finishing conditions. Tool wear, component forces and surface roughness were recorded and analysed during the machining trials. Study of the surface integrity involved physical as well as metallographic examination and analysis of the machined surfaces. The results of the machining trials show that the multi-layer (TiN/TiCN/TiN) PVD coated KC732 tools gave the best overall performance when machining both Inconel 718 and IMI 318, especially at lower feed conditions. Flank wear, excessive chipping, flaking of tool materials close to the cutting edge or on the rake face were the dominant failure modes when machining with the PVD coated tools while flank wear and notching were dominant when cutting with the CVD coated tools. These failure modes are associated with attrition, abrasion, diffusion and plastic deformation wear mechanisms acting individually or in combination during machining. The statistical regression analysis of the tool life data shows that wear of the PVD and CVD coated tools used for machining Inconel 718 was mainly affected by cutting speeds employed while cutting speed and feed rate exhibited similar influence on tool performance when machining IMI 318 with PVD coated tools. Tool life equations for each of the three coated grades when machining both superalloys under the cutting conditions investigated were derived. Severe plastic deformation and hardening of the machined surfaces occurred after machining both materials due to a combined action of increased component forces, thus increased stresses, and high temperature. Softening of the top surface layer when machining IMI 318 can be attributed to overaging of the titanium as a result of highly localised surface heating during machining. Tearing of the machined surfaces occurred when machining IMI 318 with the PVD coated tools, particularly with KC732 tools as a result of irregular flank wear and excessive chipping of KC732 tools. The self-propelled rotary tool (SPRT) incorporating K68 straight grade carbide exhibited superior wear-resistance when machining IMI 318 due to the absence of thermally related wear mechanisms caused by reduced temperature and the use of the entire edge of a round insert during rotary cutting. The minimal subsurface alterations (such as plastic deformation and hardness) when machining Inconel 718 and IMI 318 with the SPRT can also be attributed to lower cutting temperature with rotary action.

Nous avons caractérisé de manière détaillée les  fortes hétérogénéités de texture et de microstructure (macrozones) par EBSD dans des zones déformées différemment d’un disque en IMI834 de structure bimodale αP/αS, utilisé en motorisation aéronautique. Des échantillons spécifiques ont permis de montrer que l’amplitude des signaux ultrasonores rétrodiffusés dans ces échantillons dépendait de la présence et de l’organisation des macrozones. Partant de ces observations, une analyse ultrasonore des signaux rétrodiffusés dans les parties du disque soumis à de fortes déformations lors du forgeage a permis de sélectionner un jeu d’éprouvettes ayant des caractéristiques microstructurales différentes et destinées à des essais en fatigue-dwell. Une forte dispersion des durées de vie liée aux microstructures présentes a été observée. L’analyse fractographique des surfaces de rupture et leurs études par EBSD ont permis de localiser les sites d’amorçage et les chemins de propagation des fissures ainsi que leurs caractéristiques cristallographiques. Les résultats des essais en fatigue-dwell montrent que la réduction de la tenue en service est fortement influencée par la présence de macrozones formées d’agglomérats de grains αP allongés associés à des lamelles αS plus épaisses et organisées en colonies et d’autre part présentant majoritairement des axes c à moins de 30° de l’axe de sollicitation / We have characterized in detail the strong heterogeneity of texture and microstructure (macrozones) by EBSD in areas, differently deformed, of a disk in IMI834 with a bimodal structure αP/αS, used in aircraft engines. Specific samples have shown that the amplitude of back-scattered ultrasonic signals depended on the presence and organization of macrozones. Based on these observations, an analysis of back-scattered ultrasonic signals in parts of the disc subject to strong deformation during forging led to select a set of specimens with different microstructural features for fatigue-dwell tests. A high dispersion of lifetimes associated with these microstructures was observed. The fractographic analysis of fracture surfaces and their EBSD studies were used to locate crack initiation sites and propagation paths and their crystallographic characteristics. The results of fatigue-dwell tests showed that the lifetime reduction is strongly influenced by the presence of macrozones formed by agglomerates of grains elongated αP associated with thicker αS lamellae, organized in colonies and with c-axis predominantly at less than 30 ° of the solicitation axis

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- Friedrich Thießen: Der Fall Snowden oder das Ende der anonymen Welt (S. 2-3) - Sebastian Liebold: Imi Knoebel - eine Ausstellung leuchtet in den Winter hinaus (S. 23-24)

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The main target of the thesis is to find the impact of using inquiry-based science education (IBSE) on pupils' inner motivation and the level of knowledge gained for ISCED 2. To reach that, two consecutive research surveys have been held. In the first part the reaction of pupils to including an IBSE task into a regular lesson has been observed. The impact on their inner motivation has been studied. The correlation between various factors (e.g. type of school, sex) and their changes in inner motivation on observed scales has been evaluated. In the second part, the existence of statistically significant difference between experimental and control group relating the motivation of pupils to do ordinary laboratory tasks has been questioned. That was studied also after implementation of IBSE. The level of knowledge of all the pupils was examined in a similar way. Implementation of IBSE itself was evaluated by an observation of pupils while performing the implemented task as well as by standardized questionnaire Intrinsic Motivation Inventory (IMI) (McAuley et al., 1989; Ryan, 1982). Acquired data have been processed by specialised software IBM SPSS Statistics 25 (IBM Corp., 2017), choosing suitable statistical methods. The results have shown that implementing IBSE tasks in chemistry education decreases...

This diploma thesis focuses on the efficiency of the flipped classroom principle within the Chemical calculations that took place during the winter semester of the academic year 2020/2021 at the department of chemistry and chemistry didactics of the Pedagogical Faculty of Charles University. At the beginning of the thesis, the chemistry calculations are ordered into a system of chemistry education and described in the way they tend to be represented in selected textbooks for primary and secondary schools. The principle of the flipped classroom is defined and evaluated with the help of literature available. The research part of the thesis concerns itself with the students' attitudes to the flipped classroom technique applied during the Chemical calculations course. These were obtained through an IMI (Intrinsic Motivation Inventory) questionnaire as well as follow-up interviews with selected students. The thesis also explores the influence of levels of knowledge upon entering the course on their stance on the technique. At the same time the students' choice of study materials for self-education, their types and amount, is monitored. The results show that the principle of the flipped classroom is a suitable approach for the course of chemical calculations, it suits the vast majority of students. From...

Semicrystalline thermoplastic polyimides based upon bis(4-aminophenoxy)benzene and related "triphenyl ether" diamines were synthesized via the classical two step amic acid route. More specifically, polyimides were derived from para linked 1,4-bis(4-aminophenoxy)benzene, or TPEQ (triphenyl ether diamine- hydroquinone) and its meta isomer 1,3-bis(4-aminophenoxy)benzene, or TPER (triphenyl ether diamine-resorcinol). The reaction of these diamines with rigid or semi-rigid dianhydrides such as pyromellitic dianhydride (PMDA), biphenyl dianhydride (BPDA), and oxydiphthalic anhydride (ODPA) yields very thermally stable semi-crystalline polymers which have excellent resistance to organic liquids. Amorphous polyimides could be derived from hexafluoroisopropylidene-linked diphthalic anhydride (6FDA), but these systems were not extensively investigated. Importantly, molecular weight characterization of the semicrystalline systems at the soluble amic acid stage was successful by employing hydrodynamic volume calibrated, viscosity detector size exclusion chromatography (SEC). The experimental values were found to be within the targeted <M_n> range of 20-30,000 g/mole. Polyimide powders derived from these ether diamines were prepared by solution imidization at 180°C, to afford about 70% imidized structures as judged by dynamic thermal gravimetric analysis (TGA), before crystallization/precipitation occurred. Relatively small particle sizes ranging from 2 to 25 μm in size were generated, which would be appropriate for thermoplastic polymer matrix composites prepared by powder processing. All specimens showed excellent thermooxidative stability, consistent with the aromatic imide structure. The molecular design of the aromatic polyetherimide repeat unit was critical for the successful utilization of these semicrystalline high performance materials. The metba-linked TPER system when combined with the thermally stable s-biphenyl dianhydride (BPDA) produced a melting endotherm, T_m, at about 395°C, which was well within the thermal stability limitations of organic materials, i.e., less than or approximately 450°C. It was also demonstrated to be important to quantitatively endcap both ends of the chains at about 20-30,000 <M_n> with non-reactive phthalimide groups to achieve appropriate melt viscosities and good melt stability. This was done by off-setting the stoichiometry in favor of the diamine, reacting with a calculated amount of phthalic anhydride and imidizing in bulk above the Tg (≈210°C) at 300°C. These considerations allowed for remarkable melt stability in nitrogen at 430°C for at least 45 minutes, and importantly, repeated recrystallizations from the melt to afford tough, ductile semicrystalline films with excellent solvent resistance. If the macromolecular chains were not properly endcapped, it was demonstrated that viscosity increased rapidly at 430°C, suggesting reactions such as transimidization involving terminal amine end groups with in-chain imide segments and/or other side reactions, which quickly inhibited recrystallization, probably by reducing molecular transport processes. In contrast, polyimides based upon the more rigid para-linked TPEQ did not demonstrate melt or flow characteristics below 400°C, and degraded around the T_m at about 470°C! The less thermally stable TPEQ-ODPA based polyimide did melt around 409°C, and lower molecular weight samples, e.g., 10,000 M_n, recrystallized from the melt after short melt times, but cast films were brittle. It was hypothesized that the weak link may be the relatively electron rich arylene ether bond derived from the ODPA dianhydride. Several alkylated derivatives of TPER were synthesized in good yield by the reactions of alkylated resorcinol precursors with p-fluoronitrobenzene to produce dinitro compounds, which were subsequently reduced. These model diamines were then used to synthesize polyimides by the classical two step route. As expected, few of the polyimides derived from BPDA and these diamines displayed melting transitions (T_m), probably because of poor chain packing. However, they could have potential as new thermally stable membrane materials. Several amorphous polyimides prepared from 1,3-bis(p-aminophenoxy)-4-hexylbenzene were soluble in selected common organic solvents and could be cast into flexible films. / Ph. D.

- Friedrich Thießen: Der Fall Snowden oder das Ende der anonymen Welt (S. 2-3) - Sebastian Liebold: Imi Knoebel - eine Ausstellung leuchtet in den Winter hinaus (S. 23-24)