Thermal joining can lead to high thermal stresses, undesired structural changes, and the associated loss of properties. In the turbine industry, monocrystalline materials are often used to take ...advantage of their high creep resistance and heat resistance. For process-related reasons, components are mechanically machined, and the contours usually have slightly work-hardened areas due to the mechanical processing. Downstream thermal processes at temperatures above 1100 °C can lead to recrystallization (
R
x) at these areas, so that the properties are negatively affected. Usually, the joining temperatures for high-temperature brazing are in the range of 1200 °C, both in new installations and in the case of repairs. It is therefore desirable to reduce the joining temperature without changing the choice of filler material, which can lead to susceptibility to corrosion and oxidation. According to investigations of the last years, nanojoining with nanoparticles offers great potential. The joining temperature can be lowered due to the “surface effect.” A considerable reduction in the size of the particles leads to a significant increase in surface atoms and thus in the specific surface area. The connection of the materials occurs predominantly due to sintering processes. After the joining process, the properties of a bulk material are available again. Mechanical properties comparable to those of brazing have already been achieved with silver nanoparticles (Hausner in WWA 56, 2015). Up to now, publications on the topic of nanojoining have largely referred to silver nanoparticles/silver sintering. Due to the temperature application range, silver filler material cannot be used in gas turbines. Therefore, the first results of nickel nanoparticles for joining of the nickel-based superalloy PWA 1483 using induction heating are described in this paper. During joining, the parameters brazing temperature, holding time and the surface treatment of the base materials were varied. It becomes clear that the microstructure of the joint is dependent on temperature and holding time. Moreover, if the temperature is too low and holding time too short, only insufficiently sintering occurs, which leads to sample failure during the metallographic preparation. On the other hand, samples with a tensile shear strength of up to 165 MPa can be achieved with convenient joining conditions.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Nanoparticles exhibit a decrease in sintering and melting temperature with decreasing particle size in comparison to the corresponding bulk material. After melting or sintering of the nanoparticles, ...the material behaves like the bulk material. Therefore, high-strength and temperature-resistant joints can be produced at low temperatures, which is of big interest for various joining tasks. Joints (substrate: Cu) were prepared with an Ag nanoparticle-containing paste. The influence of the adjustable process parameters joining pressure, joining temperature, holding time, heating rate, thickness of paste application, surface treatment, pre-drying process, and subsequent heat treatment on the strength behavior of the joints was investigated. It is shown that in particular, the joining pressure exerts an essential influence on the achievable strengths. In addition, temperature, holding time, and thickness of paste application have a significant effect on strength behavior. In contrast, the pre-drying process, heating rate, surface pre-treatment, and subsequent heat treatment possess hardly any influence on joint strength.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Abstract
Nickel nanoparticles are materials that can be used for a novel type of joining, so called nanojoining, as an alternative to conventional brazing. The physical characteristics of these ...nano-sized particles lead to a lower melting temperature compared to nickel bulk material and even lower than typical brazes, without the need for melting point depressants. Such elements like boron or silicon cause issues due to formation of brittle intermetallic phases. In order to be able to use Ni nanoparticles in practical applications, they have to be in forms such as suspensions, e.g pastes. In the present work, therefore, a series of Ni nanopastes is prepared and investigated with emphasis on the solvent systems. These suspensions consist of Ni nanoparticles (mean diameter 20 / 90 / 180 / 300 nm) and organic compounds. The examinations show the feasibility of producing such nanopastes using ultrasound-enhanced dispersing, as well as margins for adjusting their processing properties. In addition, first results of the thermal behavior of the Ni nanopastes, measured by simultaneous DSC/TG, are shown.
Abstract
Im vorliegenden Artikel werden neu entwickelte Lote auf Eisenbasis vorgestellt, die mit Liquidustemperaturen unterhalb von 1100°C als interessante und kostengünstige Alternative zu ...kommerziellen Nickelbasisloten angesehen werden können. Vergleichende Korrosionsuntersuchungen (Stromdichte‐Potenzial‐Untersuchungen) zeigen, dass die Eisenbasislote den Nickelbasisloten mindestens analoge, meist bessere Korrosionsbeständigkeiten aufweisen. Weiterhin werden Ergebnisse aus dem dynamischen Korrosionsprüfstand nach DIN EN 15664‐1 und damit erstmals Werte für die Nickelionenabgabe von Nickelbasisloten in Trinkwasser vorgestellt. Es zeigt sich, dass diese innerhalb der in der Trinkwasserverordnung vorgeschriebenen Grenzwerte liegen.
This paper presents newly developed iron‐based brazing alloys, which are an interesting and a cost efficient alternative for commercial nickel‐based brazing alloys. Comparative corrosion studies (potentiodynamic corrosion test) show, that the iron‐based brazing alloys exhibit at least similar, but mostly better corrosion behaviour than the nickel‐based brazing alloys. Furthermore, the paper presents results from a dynamic corrosion test in conformity with DIN EN 15664‐1. The determined values show for the first time, that the release of nickel‐ions from nickel‐based brazing alloys is within the prescriptive limits of the drinking water regulation.
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6.
The Therapeutic and Working Alliances Hausner, Robert, S.
Journal of the American Psychoanalytic Association,
2000, Volume:
48, Issue:
1
Journal Article
Peer reviewed
Since their introduction, the concepts of the therapeutic alliance and the working alliance have provoked debate regarding the nature and function of these alliances and the applicability and ...validity of the concepts. Features of these concepts as originally put forth by Zetzel and Greenson, respectively, are delineated, with emphasis on the significant distinctions between them. Their relation to degree of psychopathology is examined, especially with respect to what may be understood as the more “silent” aspects of the therapeutic alliance. Mutual identification, empathy, and role-responsiveness are stressed as constituent features of the therapeutic alliance, with the working alliance seen as possible (theoretically and clinically) only after a therapeutic alliance has to some degree been established. Both alliances are understood as intrinsic structures within the analytic process, and illustrative case material is presented.
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7.
Early Alzheimer's Disease Clarfield, A Mark
The New England journal of medicine,
01/2004, Volume:
350, Issue:
1
Journal Article
Peer reviewed
Open access
To the Editor:
In the Clinical Practice article about early Alzheimer's disease, Dr. Kawas (Sept. 11 issue)
1
discusses testing for reversible causes of dementia. More than 15 years ago, it was ...conclusively shown that true reversibility of dementia, especially in the elderly, was extremely rare.
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,
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More recent work has confirmed these findings, revealing improvement in less than 1 percent of cases.
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On the basis of the evidence, one should be quite conservative, and decisions about testing should be directed primarily by the clinical clues available from the history and physical examination. Kawas cites the American Academy of Neurology's universal . . .
This article suggests that religion is best understood as comprising at least two features of human life: category and practice. Religious category and religious practice may or may not overlap in a ...given population's religious identification or ascription, but such a differentiation is highly significant and should be made in the social, political, and cognitive study of religion. Three examples are offered whereby religious category and religious practice need to be distinguished in order to understand the ethnographic data. Rather than seeing religion as an undifferentiated or singular phenomenon classified by type, category and practice should be considered fundamental elements of religiosity that are both connected to and distinct from one another. The cases are drawn from Nepalis in the UK: The example of Nepali religion, in Nepal and in the diaspora, forms a complex set of categories and practices that testify to their distinctiveness and to their interaction.
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