Regeneration of High Pressure Turbine Blades. Development of a Hybrid Brazing and Aluminizing Process by Means of Thermal Spraying

Besides welding, high temperature vacuum repair-brazing is already established for nickel-based alloy turbine blades in the aerospace and power plant industries. After the worn turbine blade has been decoated to its substrate material, the filler metal is deposited as a paste, (melt-spin) foil or tape which also consists of a nickel-based alloy. Following this, the hot-gas corrosion protective coating (e.g. NiCoCrAlY) is applied using thermal spraying. The brazed turbine blade is ground or milled to size and subsequently aluminized to further increase its corrosion resistance. Using the current state of technology, a turbine blade can undergo approximately 3 to 4 repair cycles. In the present study, the development of a two-stage hybrid technology for repairing turbine blades is considered which incorporates, on the one hand, a process technology and manufacturing aspects and, on the other hand, considers material-technological mechanisms. During the first stage of this hybrid technology, the filler metal together with the hot-gas corrosion protective coating is applied using thermal spraying. The subsequent second stage combines the brazing and aluminizing processes. The technology developed here brings technical and economic advantages whilst enabling the current state-of-the-art's corresponding process chain for repairing turbine blades to be shortened.DFG/SFB/87

Brazing in SiH4-Doped Inert Gases: A New Approach to an Environment Friendly Production Process

Engineering under protective atmospheres or in vacuum allows the production of materials and components, where the absence of oxygen is an essential requirement for a successful processing. Ideally, joining or coating of (and with) metallic materials needs oxide free material surfaces, in order to achieve durable joints or coatings. Using the established technology of brazing in controlled atmosphere, fundamental physical mechanisms for deoxidation of metal surfaces are presented and the role of oxygen and water residue in the process atmosphere is analyzed. Furthermore, the doping of gases with monosilane for generating virtually oxygen-free process atmospheres is introduced and its advantages for an oxygen-free production are discussed. © 2019, The Author(s)

Health-related quality of life and functional impairment in acute vestibular disorders

BACKGROUND AND PURPOSE Acute vestibular symptoms have a profound impact on patients' well-being. In this study, health-related quality of life (HRQoL) and functional impairment were investigated prospectively in patients with different peripheral and central vestibular disorders during the acute symptomatic stage to decipher the most relevant underlying factors. METHODS In all, 175 patients with acute vestibular disorders were categorized as central vestibular (CV, n~=~40), peripheral vestibular (PV, n~=~68) and episodic vestibular disorders (EV, n~=~67). All patients completed scores to quantify generic HRQoL (European Quality of Life Score Five Dimensions Five Levels, EQ-5D-5L) and disease-specific HRQoL (Dizziness Handicap Inventory, DHI). Vestibular-ocular motor signs were assessed by video-oculography, vestibular-spinal control by posturography and verticality perception by measurement of subjective visual vertical. RESULTS Patients with PV had a poorer HRQoL compared to patients with CV and EV (EQ-5D-5L/DHI: PV, 0.53~±~0.31/56.1~±~19.7; CV, 0.66~±~0.28/43.3~±~24.0; EV, 0.75~±~0.24/46.7~±~21.4). After adjusting for age, gender, cardiovascular risk factors and non-vestibular brainstem/cerebellar dysfunction patients with PV persisted to have poorer generic and disease-specific HRQoL (EQ-5D-5L -0.17, DHI +11.2) than patients with CV. Horizontal spontaneous nystagmus was a highly relevant factor for subgroup differences in EQ-5D-5L and DHI, whilst vertical spontaneous nystagmus, subjective visual vertical and sway path were not. EQ-5D-5L decreased significantly with more intense horizontal subjective visual vertical in CV (rho~=~-0.57) and PV (rho~=~-0.5) but not EV (rho~=~-0.13). CONCLUSIONS Patients with PV have the highest functional impairment of all patients with acute vestibular disorders. Vestibular-ocular motor disturbance in the yaw plane has more impact than vestibular-spinal or vestibular-perceptive asymmetry in the roll and pitch plane, suggesting that horizontal visual stability is the most critical for HRQoL

Potentiale und Eigenschaften des Lichtbogenspritzens in silandotierten Inertgasen

Neben den funktionalen Eigenschaften ist die Haftfestigkeit eines der wichtigsten Kriterien für den industriellen Einsatz von thermisch gespritzten Schichten. Da konventionelle thermische Spritzverfahren fast ausschließlich an Luftatmosphäre durchgeführt werden, führt dies zur Oxidation der Spritzpartikel und der Grenzflächen innerhalb der aufgespritzten Schichten. Konventionelle thermisch gespritzte metallische und metallkeramische Schichten weisen daher eine heterogene Schichtmorphologie mit interlamellaren Oxidsäumen sowie ein eingeschränktes Benetzungsverhalten am Schicht-Substrat Interface auf. Dies hat einen entscheidenden Einfluss auf die Bindungsmechanismen thermisch gespritzter Schichten. Ziel dieser Arbeit ist es, das Potential von thermischen Spritzprozessen in einem Gemisch aus Silan und einem Inertgas bei Umgebungsdruck als Alternative zu den bekannten Vakuum- und Kaltgasspritzverfahren darzustellen. Am Beispiel von lichtbogengespritzten Schichten wird gezeigt, dass der resultierende extrem niedrige Sauerstoffpartialdruck in der silandotierten Prozessatmosphäre die Oxidation während des Beschichtungsprozesses unterdrückt. Dies führt zu Schichten mit reduzierter Porosität und deutlich verbesserten Eigenschaften. Ferner werden so Bedingungen geschaffen, die die Applikation von hochsauerstoffaffinen Werkstoffen mit dem Lichtbogenspritzen erst ermöglichen

Future challenges in colloid and interfacial science

This article deals with topics where I expect special future challenges, exemplifying these by experiments out of my own department. One area where I expect large progress also in view of many technical developments in the past concerns the understanding of the structure of fluid interfaces at the atomic level. It is shown by non-linear optical spectroscopies that the free water surface is ice-like and can be “liquefied” by ion adsorption. X-ray fluorescence from the interface demonstrates that ion binding is very specific which cannot be explained by existing theories. A second major area are nonequilibrium features, and one of the old and new ones here is nucleation and growth. This presentation concentrates on effects produced by ultrasound, a well-defined trigger of gas bubble formation. It exhibits high potential for chemistry at extreme conditions but with a reactor at normal conditions. It has special importance for treatment of surfaces that can be also manipulated via controlled surface energies. A third area will concern complex and smart systems with multiple functions in materials and biosciences. As next generation, I anticipate those with feedback control, and examples on this are self-repairing coatings

Herringbone ordering and lattice distortions in a planar-molecule model for Langmuir monolayers

A model of planar molecules, made up of "atoms" interacting by Lennard-Jones potentials and arranged to mimic the cross section of alkyl chains, is used to study the problem of backbone plane ordering in Langmuir monolayers. It is shown that two minima of the interaction energy are reached if molecules lie on the sites of a centered rectangular lattice in a herringbone configuration with two different dihedral angles. These orientationally ordered phases can be related to the so-called herringbone and pseudoherringbone structures, whose lattice distortions qualitatively agree with those determined by means of grazing incidence x-ray diffraction experiments on Langmuir monolayers. A third energy minimum is obtained for a configuration of parallel molecules on an oblique lattice, which has also been observed in some experiments. The competition between the three phases is investigated, upon varying geometric parameters of the model molecules and surface pressure. The effect of temperature is analyzed in a mean field approximation, by taking into account the orientational entropy contribution on a lattice system with variable unit cell parameters. In this framework the transition to an orientationally disordered phase is also pointed out

Stabilization of tilt order by chain flexibility in Langmuir monolayers

Langmuir monolayers are modeled as systems of short chains, which are confined to a planar surface at one end, but free to move within the plane. The phase behavior is calculated in a mean field approximation, which combines the self consistent field method with elements of classical density functional theory. It is shown that phases with tilt order are unstable in systems of stiff chains, but can be stabilized by chain conformational entropy in systems of sufficiently flexible chains. The chain entropy is also responsible for the appearance of an additional untilted phase, the liquid expanded phase. The region of stability of the different phases is discussed, and their microscopic structure is analyzed in some detail.Comment: to appear in Phys. Rev.

Metalloporphyrin intercalation in liposome membranes: ESR study

Liposomes characterized by membranes featuring diverse fluidity (liquid-crystalline and/or gel phase), prepared from egg yolk lecithin (EYL) and dipalmitoylphosphatidylcholine (DPPC), were doped with selected metalloporphyrins and the time-related structural and dynamic changes within the lipid double layer were investigated. Porphyrin complexes of Mg(II), Mn(III), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), and the metal-free base were embedded into the particular liposome systems and tested for 350 h at 24°C using the electron spin resonance (ESR) spin probe technique. 5-DOXYL, 12-DOXYL, and 16-DOXYL stearic acid methyl ester spin labels were applied to explore the interior of the lipid bilayer. Only the 16-DOXYL spin probe detected evident structural changes inside the lipid system due to porphyrin intercalation. Fluidity of the lipid system and the type of the porphyrin complex introduced significantly affected the intermolecular interactions, which in certain cases may result in self-assembly of metalloporphyrin molecules within the liposome membrane, reflected in the presence of new lines in the relevant ESR spectra. The most pronounced time-related effects were demonstrated by the EYL liposomes (liquid-crystalline phase) when doped with Mg and Co porphyrins, whereas practically no spectral changes were revealed for the metal-free base and both the Ni and Zn dopants. ESR spectra of the porphyrin-doped gel phase of DPPC liposomes did not show any extra lines; however, they indicated the formation of a more rigid lipid medium. Electronic configuration of the porphyrin’s metal center appeared crucial to the degree of molecular reorganization within the phospholipid bilayer system

Diverse Applications of Nanomedicine

The design and use of materials in the nanoscale size range for addressing medical and health-related issues continues to receive increasing interest. Research in nanomedicine spans a multitude of areas, including drug delivery, vaccine development, antibacterial, diagnosis and imaging tools, wearable devices, implants, high-throughput screening platforms, etc. using biological, nonbiological, biomimetic, or hybrid materials. Many of these developments are starting to be translated into viable clinical products. Here, we provide an overview of recent developments in nanomedicine and highlight the current challenges and upcoming opportunities for the field and translation to the clinic. \ua9 2017 American Chemical Society