Einkristalline Gasturbinenschaufeln aus Nickelbasis-Legierungen. Teil II: Wärmebehandlung und Eigenschaften

Single-Crystal Blades for Gas Turbines Part II: Heat Treatment and Properties The article gives an overview of current single-crystal technology used in fabricating highly stressed blades and vanes for gas turbines. After a short outline of the demands placed on gas turbine blades and the resulting necessity for improvement of nickel-base alloys, and following a short definition of the “technical” single-crystal, the principal of directional solidification with suitable methods of grain selection and the realizable solidification front morphologies were described in Part I. The usuable range of casting parameters for industrial production was fixed using the alloy SRR99 as an example. The major mictrostructural characteristics of single-crystal comoponents made of nickel-base alloys namely crystallographic orientation, microporosity, morphology of the γ′-hardening phase, dendritic segregation and residual eutectic were presented. After casting, the microstructure is not in a condition which yields optimum service properties. Therefore, heat treatment is necessary. Part II describes how, with appropriate heat treatment, residual eutectic can be dissolved, segregations homogenized and the morphologly of the γ′-phase optimized. Finally, the mechanical properties are discussed. The dominant influence of the crystallographic anisotropy on elastic and plastic properties are shown as well as the dependence of the creep behaviour on the morphology of the γ′-phase and the correlation between fatigue strength and microporosity.     

Spanende Bearbeitung von Hartlegierungen – Drehen und Schleifen. Teil I: Gefüge und Eigenschaften von Hartlegierungen

Metal Cutting of Hard Alloys – Turning and Grinding. Part I: Structure and Properties of Hard Alloys Hard alloys count among the materials that contain hard phases. This involves primary and/or eutectic hard phases embedded in a metallic matrix. The characteristics of the individual microstructural constituents may be combined to form a material featuring excellent wear resistance and a high resistance to fracture. For that reason, the material can be widely used in all applications where the wear resistance to abrasion is essential. In the event low operating temperatures are involved the component costs to service life ratio speaks for hard alloys on Fe basis. Above 600 °C heat resistant Ni and Co matrices are to be given preference. Carbides and borides of the transition metals are specially suited as hard phases. They attach well to the surrounding matrix. Nowadays, alloys of the FeCrC system are primarily employed for economic reasons. As nickel-based material the NiCrSiB alloying system is frequently employed. Hard alloys on cobalt basis usually belong to the CoCrWC (stellite) system. In many fields of application components of this material group require a largearea metal cutting technique (eg for barrel extruders, crushing rollers, valve seats). However, problems may be encountered during machining due to the high hardness and excellent wear resistance of this material. The structural difference between hard phases and metallic matrix causes different reactions to stresses exerted during the machining process. Process-related changes of the microgeometric surface characteristics and the physical condition of the surface zone of a material are paraphrased by the term “surface integrity”. To create a basis for assessing the machining influence on the multiphase component surface layer, the first part of the paper discusses manufacturing techniques, constitution of the microstructure and main properties of the individual structural components.     

Oberflächenschutzschichten für metallische Hochtemperatur-Werkstoffe. Teil 1: Entwicklungstendenzen,Prüfung und Herstellung von Schutzschichten

Protection of High Temperature Metallic Materials against Oxidation . Part 1: Development Trends, Testing and Preparation of Protective Layers. A comparison is given of the chemical compositions of industrial Co- and Ni- high-temperature alloys used in the past years. Due to their relatively low Cr and Al contents the more recent super-alloys require additional oxidation protection. Theoretically, the refractory metals would allow much higher working temperatures than the super-alloys, but alloys based on such metals need a much more perfect oxidation protection. The fabrication testing and methods for such protective layers are briefly reviewed. The second part of this paper will describe some specific protective layers for super-alloys and refractory metals.     

Mit Hochfrequenz angeregte Niederdruckplasmen: Prinzipien und Strukturierung von Halbleitern. Teil I

In two parts, the generation of cold plasmas by capacitive and inductive coupling as well as by absorption of whistler waves is outlined. In the third part, it is shown how the knowledge of these mechanisms can be exploited for modifying the surfaces of semiconductors.     

Hochtemperatur-Supraleitungs-Technologie — Herstellung und Anwendungspotentiale

The discovery of high-temperature-superconductors, which exhibit a transition temperature above 77 K, was supposed to be the best way to achieve superconductivity at room temperature. The research of the recent years turned out, that further problems have to be solved. Especially the layered structure of the new ceramic superconductors reveals in several drawbacks in the preparation techniques. The purpose of this article is to give a comprehensive overview about different preparation techniques of high temperature superconductors. A summary of their cryoelectronic applications will be presented.     

Korrosion in Carbonsäuren. Teil I: Anwendung von Radionuklidtechnik und Impedanzspektrometrie auf Korrosionsuntersuchungen metallischer Werkstoffe

Corrosion in Carboxylic Acids – Part I: The Application of Radionuclide Techniques and impedance Spectrometry in Corrosion Studies of Metallic Materials Within the ?Corrosion and Protection”? research and development program, studies have been conducted on the corrosion of metals in low carboxylic acids. A radionuclide method has been employed to measure corrosive abrasion, and the technique of impedance spectrometry has been used to trace the electrochemical corrosion reactions. In this first communication, these methods of measurement are described and their uses and the kinds of information to be obtained from them are discussed. The corrosion systems studied, i.e., some high-alloy steel grades and nickel base alloys in formic acid and acetic acid with a number of additives, are indicated.