W. Gust

Untersuchung der thermodynamischen Eigenschaften flüssiger gallium-zinn- und gallium-wismut-Legierungen

Zusammenfassung Zur Ermittlung der thermodynamischen Eigenschaften flussiger Ga-Sn- und Ga-Bi-Legierungen wurden zunachst die integralen Mischungsenthalpien mit einem Hochtemperatur-Kalorimeter direkt gemessen und unter Verwendung der gewonnenen Daten die ubrigen Uberschussfunktionen durch Auswertung der Schmelzgleichgewichte gewonnen. Die Mischungsenthalpien sind in beiden Systemen positiv. Die maximalen Werte betragen fur das System Ga-Sn ΔH max = 234 cal/g-Atom und fur das System Ga-Bi ΔH max = 504 cal/g-Atom. Die Uberschussentropien flussiger Ga-Sn-Legierungen haben ein positives Vorzeichen ( ΔS ex max = +0,25 cal/g-Atom °K), wahrend im mittleren Konzentrationsbereich des Systems Ga-Bi negative ΔS ex− Werte gefunden werden ( ΔS ex max = −0,2 cal/g-Atom °K). Die Diskussion der Faktoren, die das thermodynamische Verhalten einer Legierung bestimmen, fuhrte zu der Annahme, dass die Mischungsenthalpien in beiden Systemen im wesentlichen durch den Einfluss einer atomaren Fehlpassung in der Schmelze infolge vorhandener Atomvolumenunterschiede bedingt sind.

Sims-untersuchungen zur volumendiffusion von Al in Ge

Zusammenfassung Mittels Sekundarionen-Massenspektrometrie (SIMS) wurde die Volumendiffusion von Al in Ge untersucht. Es wurden 17 mit Al bedampfte Ge-Einkristalle bei Temperaturen zwischen 827 und 1178 K ausgelagert. Danach wurden die Konzentrationsverlaufe mit einem Cameca SMI 300-Sekundarionen-Massenspektrometer aufgenommen. Die daraus ermittelten Diffusionskoeffizienten lagen zwischen 8,2·10 −19 und 1,3·10 −12 cm 2 /s. Aus deren Temperaturabhangigkeit ergeben sich die Diffusionskenngroβen zu ΔH = 3,45 ± 0,04 eV und D 0 = (1,0 ± 0,5)·10 3 cm 2 /s, die mit Literaturwerten verglichen werden.

Techniques for the production of oriented bicrystals and results on specimens prepared by these methods

Abstract A sintering technique has been developed for the production of oriented bicrystals of macroscopic thickness (several mm or more) from single crystalline material. Since the surfaces which are sintered together to form the interface have dimensions of the order of 10 mm, their flatness is of primary importance if satisfactory results are to be obtained. By using various techniques for surface preparation and sintering, bicrystals of Ni, Ag, Cu and Cu based solid solutions have been successfully produced. The methods result in boundaries that are generally very flat over large areas. Boundary orientation is thus well defined. The results of some initial investigations using these bicrystals are presented. These include the determination of the grain boundary diffusion coefficient for In in a Ni bicrystal using secondary ion mass spectrometry (SIMS) and measurements of the growth kinetics for the discontinuous precipitation reaction in a Cu-In bicrystal.

Masked deposition of decorative coatings on large area glass and plastic sheets

An industrial installation for vacuum arc deposition is presented. Its potential in the field of decorative coatings for large area glass and plastic sheets is demonstrated, particularly its ability to deposit the patterned coatings with the aid of a textile polymeric mask. Titanium nitride, titanium dioxide and bilayer TiN/TiO2 coatings on silica glass have been characterized in terms of composition and corrosion resistance. The corrosion resistance of TiN coatings is higher than the corrosion resistance of TiO2. The corrosion resistance of vacuum arc deposited TiN coatings on glass prove to be higher than that of TiN coatings produced by DC reactive sputtering and plasma assisted chemical vapour deposition. Mask-deposited TiN coatings do not show any signs of accelerated corrosion along the border between coated and uncoated glass. q 1999 Elsevier Science S.A. All rights reserved.

Stable and metastable phases in the vacuum arc deposited Co thin films

The Co coatings were produced with the aid of the vacuum arc deposition and studied by transmission electron microscopy and electron back-scattering diffraction. At large distances from the cathode, the deposition rate R of Co is comparable with R values for dd vacuum arc deposited Mo and Ni-Ti alloys and exceeds R obtained in magnetron sputter deposition. The vacuum arc deposited coatings d are formed from the multiply-charged ion flux and microparticles. The Co film formed from ions consists of a hexagonal close packed . phase and possesses a dense microstructure with uniform and extremely small 5 nm grains. The Co microparticles solidified after collision with a substrate have a metastable face centered cubic structure. q 1998 Published by Elsevier Science S.A.

Hall current accelerator for pre-treatment of large area glass sheets

Abstract A large aperture Hall current accelerator has been developed for cleaning glass sheets before vacuum arc deposition of decorative layers. Hall current source advantages towards Kaufmans one in industrial processes are emphasized. Source ‘sputter profiles’ are given for silica glass and poly(methyl metacrylate). Sputter cleaning of aluminum has been characterized in terms of roughness and microhardness variation.

LOCAL VALUES OF THE DIFFUSIVITIES AT THE MIGRATION FRONT OF THE DISCONTINUOUS PRECIPITATES IN Al-22 at.% Zn ALLOY

Diffusion along migrating grain boundaries is a rate-controlling factor in many solid-solid phase transformations like discontinuous precipitation (DP), discontinuous dissolution (DD) and diffusion-induced grain boundary migration. In this paper it will be shown that some divergence between the tracer diffusivities obtained by the sectioning technique and the chemical diffusivity data obtained from DP and DD processes can be removed by applying a local concept for the determination of the kinetic parameters for these reactions. It means that the solute concentration in the {alpha} solution will be measured for the same individual cell whose solute profile across the {alpha} lamella was determined in the former DP process. An Al-22 at.% Zn alloy was chosen for the investigation for which reliable data for the tracer diffusivity of stationary grain boundaries of Al-Zn solid solutions over a wide range of zinc content were previously reported. As the DP and DD reactions are also well documented, the Al-Zn system is particularly useful for studies of the mutual relation between the diffusivities of stationary and moving grain boundaries.

Ausscheidungsverhalten von W-Cr-Mischkristallen

Zusammenfassung Es wurde das Ausscheidungsverhalten von W-Cr-Mischkristallen mit sechs verschiedenen Konzentrationen zwischen 20 und 70 At.% W untersucht. Im Temperaturbereich zwischen 1100 und 1493 K kann bei allen Proben eine feinlamellare diskontinuierliche Ausscheidungsreaktion festgestellt werden; eine kontinuierliche Ausscheidung wurde nicht beobachtet. Bestimmt wurden der Lamellenabstand l , die Wanderungsgeschwindigkeit v der Reaktionsfront sowie die Restubersattigung in den Lamellen. Uber den gesamten Konzentrationsbereich wurden Gitterkonstantenbestimmungen durchgefuhrt. Es wird der Nachweis erbracht, dass die bisher angenommene Lage des kritischen Punktes der Mischungslucke nicht den tatsachlichen Verhaltnissen entspricht, sondern um ca . 150 K zu tief liegt. Mit den experimentell bestimmten Daten wurde nach verschiedenen Modellvorstellungen der Volumendiffusionskoeffizient D v bzw. die Grosse λ D I fur die Grenzflachendiffusion in der Reaktionsfront berechnet. Ein Vergleich mit gemessenen Diffusionsdaten des Systems Mo-Cr legt den Schluss nahe, dass es sich bei der hier vorgefundenen diskontinuierlichen Ausscheidung um eine grenzflachendiffusionskontrollierte Reaktion handelt. Die nach den verschiedenen Modellen erhaltenen Mittelwerte der Aktivierungsenthalpie Q I der Grenzflachendiffusion liegen zwischen 304 und 454 kJ mol −1 und haben als Funktion der Konzentration zwischen 30 und 40 At.% W ein Minimum.

Vacuum arc deposition of protective layers on glass and polymer substrates

Abstract Vacuum arc deposition allows one to deposit various coatings on insulating and temperature-sensitive substrates (like polymers). An advantage of the vacuum arc deposition technique is the low substrate temperature during the deposition process. A vacuum arc deposition apparatus for the coating of large-area substrates has been developed. Ti, TiN, TiO 2 and diamond-like single and multilayer coatings have been deposited on plastic and glass substrates. The vacuum arc technology permits formation of multilayer colour filters of high uniformity on substrates with dimensions up to 2000×1400 mm 2 . The microstructure, chemical composition and optical properties of the deposited coatings have been characterised with the aid of secondary-ion mass spectrometry, optical and Raman spectroscopy, and scanning electron microscopy.

ABNORMAL GRAIN GROWTH IN AL OF DIFFERENT PURITY

Abstract The transition from normal to abnormal grain growth has been studied in four Al alloys of various purity (2N, 3N, 4N and 5N). The temperature and time for the onset of abnormal grain growth depend strongly on the deformation and homogenization treatment. Generally, the formation of large grains before cold rolling makes easier the transition to abnormal grain growth during the subsequent annealing. The abnormal grain growth can take place only above a certain temperature which decreases with increasing alloy purity. The onset time of the abnormal grain growth decreases with increasing temperature. It can be qualitatively explained by the dissolution of submicron particles of a second phase.