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Spectroscopic ellipsometry of interfacial phase transitions in fluid metallic systems: KxKCl1-x and Ga1-xBix [online]

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ISBN: 3937300082 Year: DOI: 10.5445/KSP/812004 Language: ENGLISH
Publisher: KIT Scientific Publishing
Subject: Chemistry (General)
Added to DOAB on : 2019-07-30 20:01:59

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Abstract

The investigation of the interfacial phase transitions in fluid systems with short-range intermetallic interactions are of great interest. The phenomena were studied in two systems exhibiting a liquid-liquid miscibility gap: at the fluid/wall interface in fluid KxKCl1-x and at the fluid/vacuum interface of the Ga1 xBix alloys. To characterize the interfacial changes of the ultra thin films (composition, thickness and their evolution with time) the spectroscopic ellipsometry was performed over a wide spectral range. Whereas in the experiments on KxKCl1-x an existing ellipsometer could be used, a completely new UHV-apparatus including the in-situ phase modulation ellipsometer had to be developed for Ga1 xBix alloys. For the KxKCl1-x system new results on complete wetting at solid-liquid coexistence as well as in the homogenous liquid phase (prewetting) are presented. The spectra show the typical F center absorption which indicates that the film is a salt-rich phase. The thickness strongly increases approaching the monotectic from 30 to 440 nm, which is in agreement with the tetra point wetting scenario. For this interpretation a quantitative description of the excess Gibbs energy has been developed. For the Ga1 xBix system the results on complete wetting, surface freezing and oscillatory interfacial instabilities are presented. The high-precision spectra have been recorded approaching the liquid-liquid miscibility. These spectra have been modeled using a Ga-Bi effective medium approximation for the substrate covered by a film of liquid Bi. The measurements give evidence of tetra point wetting in the Ga-Bi system. First ellipsometric study of the surface freezing in Ga-Bi has been performed. Within the miscibility gap a very interesting effect of surface and bulk oscillatory instability was observed. The details of this process at present are not well understood, but a qualitative description is given.

Development of Microactuators Based on the Magnetic Shape Memory Effect

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Book Series: Schriften des Instituts für Mikrostrukturtechnik am Karlsruher Institut für Technologie / Hrsg.: Institut für Mikrostrukturtechnik ISSN: 18695183 ISBN: 9783731501251 Year: Volume: 21 Pages: X, 153 p. DOI: 10.5445/KSP/1000036883 Language: ENGLISH
Publisher: KIT Scientific Publishing
Subject: Technology (General)
Added to DOAB on : 2019-07-30 20:01:58
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The giant magneto-strain effect in Ni-Mn-Ga alloys is particularly attractive for actuator applications. Two different approaches are being pursued to develop MSM microactuators. To observe large deflections of Ni-Mn-Ga microactuators, the material should be exhibiting low twinning stress and large magnetic anisotropy. In addition, design rules and boundary conditions for operating the Ni-Mn-Ga actuator material are having significant importance for evolution of performance characteristics.

Entwicklung miniaturisierter Aktorsysteme basierend auf magnetischen Formgedächtnislegierungen

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Book Series: Schriften des Instituts für Mikrostrukturtechnik am Karlsruher Institut für Technologie / Hrsg.: Institut für Mikrostrukturtechnik ISSN: 18695183 ISBN: 9783731505006 Year: Volume: 33 Pages: XI, 203 p. DOI: 10.5445/KSP/1000053101 Language: GERMAN
Publisher: KIT Scientific Publishing
Subject: Technology (General)
Added to DOAB on : 2019-07-30 20:01:59
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In this work, the actuation principles of single-crystal Ni-Mn-Ga alloys based on the magnetic shape memory effect (MSM-effect) and the coupling between their magnetic, mechanical and thermal properties, are investigated. The MSM effect is generated by the magnetically induced reorientation of the crystal structure. Thereby, the magnetic strain up to 10 % can be reached.

Schädigung und Lebensdauer von Nickelbasislegierungen unter thermisch-mechanischer Ermüdungsbeanspruchung bei verschiedenen Phasenlagen

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Book Series: Schriftenreihe des Instituts für Angewandte Materialien, Karlsruher Institut für Technologie ISSN: 21929963 ISBN: 9783731504450 Year: Volume: 53 Pages: IX, 149 p. DOI: 10.5445/KSP/1000049869 Language: GERMAN
Publisher: KIT Scientific Publishing
Subject: Technology (General)
Added to DOAB on : 2019-07-30 20:02:02
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This work considers the behaviour of two nickel-base alloys under thermo-mechanical fatigue loading with varying phase angles between mechanical strain and temperature. The investigations focus on the characterisation of microstructures and damage mechanisms as a function of the phase angle. Based on the results, a life prediction model is proposed.

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