Maßänderungen von Zinkdruckgußlegierungen infolge von Alterung

Changes in dimension of zinc die-casting alloys due to aging . It is known since a long time that die-cast elements are subject to slight changes in dimension even when they are made of high-grade zinc alloys standardized for that purpose. But in prior research it was apparently still unknown that the amount of these changes is influenced, among other things, by the cooling conditions of the pieces following the casting process. It is therefore impossible to compare off-hand the values coming from different sources. The changes in dimension were reinvestigated for that reason with regard to the cooling conditions, and the results were some new findings in this field.     

Verschleißverhalten von Innenbüchsenwerkstoffen für das Strangpressen von Nichteisenmetallegierungen

Wear Resistance of Liner Material for Extruding Non-ferrous Alloys Extruding Al and its alloys Cu, brass, Cu-Ni alloys and Ni on account of variable working conditions (as temperature) different liner materials are used. Processing Al martensitic hot work steels are successful in application. Working up copper high temperature resistant and austenitic steels are additional in use. The high-temperature strength of these materials is well-known. Based on the investigation of the high-temperature wear this paper presents several new considerations.     

Untersuchung von Oberflächenschutzschichten von Gasturbinenlegierungen

Investigations on protective coatings on gasturbine alloys. It has been found by investigations of specimens of a combustion chamber pilot plant and also by experiences with gasturbines that aluminide or chromium aluminide coatings are only slightly protective under working conditions of industrial gasturbines. Chromium coatings have a distinctive better protective efficacy and are surpassed in this quality by silicide coatings. It was possible to give information on the development of silicide phases on Nimonic 105. Under the conditions of corrosive attack a surface layer of Nickelolivine is formed and the silicide phases are changed in direction of ternary phases. Even when chromium sulfides are formed in the silicide layer the specimens are stable under the test conditions. By investigations on an airfoil made from B 1900 with a protective coating of Aluminium and Silicon the presence is shown of a ternary Laves phase with Silicon.     

Zur Plastoermüdung von Stahl unter dem Einfluß von Druckwasserstoff

Low Cycle Fatigue of Steel in Hydrogen Environment The low cycle fatigue fracture of a medium strength tempered steel ist studied in compressed hydrogen resp. nitrogen (150 bar). For given strain amplitudes, hydrogen reduced strongly the cycles to failure. Probably the crack growth is accelerated rather than the crack initiation. The frequency had no influence on the number of cycles to failure.     

Verarbeitung von feinen Spritzwerkstoffen zur Verbesserung von Korrosions‐ und Verschleißschutzeigenschaften von thermisch gespritzten Schichten

About the application of fine spray materials for improvements in terms of corrosion and wear protection of thermal spray coatings Within a research project the spray materials Cr₂O₃, Cr₃C₂ NiCr and WCCoCr were considered. Process parameters were determined, optimized and validated allowing the application of very fine spray material fractions (< 25 μm) with plasma and high velocity oxy‐fuel spray systems. In addition to improved coating properties like low porosity and improved corrosion resistance the application of near net shape coatings was enabled. The subsequent reduced effort for after‐treatment of the coatings can contribute to further rationalization of thermal spray processes.     

Einfluß von Sauerstoffspuren auf die Eigenschaften von Wolfram-Schwermetallen

Influence of Oxygen Traces on the Properties of Tungsten Heavy Metals Investigation carried out with differently sintered W heavy metals showed that careful pre-reduction before liquid phase sintering is essential for obtaining satisfactory mechanical properties; otherwise oxide layers at the phase boundaries deteriorate the interface strength and thus cause premature fracture. Understandably, the water vapour content of the furnace atmosphere is of considerable importance. Appropriate sintering anticipated, even severely oxidized green compacts result in highly ductile heavy metals. Addition of scavengers, e.g. Cr or V, instead of the pre-reduction improves the interface strength, the mechanical properties however remain unsatisfactory.     

Einsatz von Mikroplasmen für die Herstellung von Silizium‐Mehrlagenaufbauten

Micro Plasma Processes for MEMS Packaging The encapsulation of MEMS devices can be difficult, since released micromechanical parts (e.g. membranes, valves, and cantilevers) tend to stick to the surrounding surfaces. Area‐selective surface modification is a new approach, developed by the Fraunhofer‐Institute for Surface Engineering and Thin Films (IST), to overcome these problems. From a more general point of view, area‐selective surface tailoring with microplasmas is an attractive topic for micro systems production. The business transfer of the technique by implementation into the SU SS mask is currently being evaluated.     

Teilautomatisiertes preforming zur Qualitätssicherung und Verkürzung von Fertigungszeiten bei der Herstellung von Rotorblättern von Windenergieanlagen

Quality management and reduction of processing time through automised preforming in the rotorblade manufacturing for wind turbines Rotor blades of wind turbines are mainly manufactured from fibre reinforced plastics. These materials show an excellent performance concering the ratio of stiffness and weight. Basically the composite material of rotor blades is made out of glass fibres and thermosetting material. But growing technological and economical requirements to rotor blades by off‐shore‐application, in particular through increasing rotor blade diameter, have to meet successful. Although reduction of processing time and increased quality of rotor blades play a major role. To achieve the increasing requirements of the rotor blade manufacturing the Bremen Institute for Engineering Design and the rotor blade manufacturer Abeking & Rasmussen Rotec GmbH are working together on the handling and manufacturing of textile preforms. Preforms are made out of stacked and bonded dry textile layers and deposited in the mould as one textile part. Preforming allows the parallel processing of some manufacturing steps. This shows great advantages in the production of fibre reinforced plastics because of the long curing time of the resin component. This parallel processing is required to reach the aim of decreased overall cycle time. This essay is focussing on the handling of textiles and the textile preforming. Summarised aspects of quality management and economics in textile preforming will be discussed with the aim of automising the preforming process.     

Rückgewinnung von Vinylchloridmonomer

The production of the polymer polyvinylchloride (PVC) emits a high amount of waste gas. The recovery of the evaporated base product vinylchoridemonomer (VC) is an important aspect for the economics of the whole process. Membrane and vacuum technology improve the efficiency and the economics of the recovery process considerably.     

Ultraschallprüfung von Hochleistungsverbundwerkstoffen

Ultrasonic Examination of High Performance Polymer Composites A report is given about the ultrasonic examination of high performance polymer composites with the computer aided test system ABAKUS. Details of the hardware and software are described. It is stated that the test frequency is one of the important parameters. When using the through transmission technique under water, a high sensitivity is obtainable by masking the receiving probe. In addition the interpretation of the results becomes easier by image treatment with the software module GMANI. The goal is a fully automated evaluation.     

Ultraschallschweißen von Kontaktwerkstoffen

Ultrasonic Welding of Contact Materials . Ultrasonic welding of metals has found only a few industrial applications until now. Today however ultrasonic welding equipments with high power output for the welding of thicker parts are available. Contact materials have been welded ultrasonically on various base materials, e. g. silver and silver alloys on copper and copper alloys and aluminium. Bond quality was determined by shearing off the contact plates from the base material. Metallographic investigations and microhardness measurements were made to examine the bonding mechanisme. Ultrasonic welding will be a very good supplementary method in contact technology mainly for the welding of hardly weldable components like AgCdO or Al.     

Komplexe Bewertung von Indentereindrücken zur Charakterisierung von Konstruktionskeramik

The induction of indentations in brittle materials and their evaluation result in information useful for the characterization of materials. In addition to the fracture-mechanical evaluation of the indentations, i.e. of the incipient cracks resulting from them, which cracks are used for determining the fracture toughness. Information regarding the hardness, critical size of surface defects, characteristic quantities of crack propagation, durability as well as existing internal stresses can be derived.     

Einfluß von Schweißen und Kaltumformung auf das Kurzzeitschwingfestigkeitsverhalten von austenitischem Stahl

Influence of Welding and Cold Forming on the Low-Cycle-Fatigue Behaviour of Austenitic Steel The low-cycle-fatigue behaviour of the austenitic steel X 10 CrNiTi 189, as received and welded, was investigated after cold forming up to 10 per cent by strain controlled tests. The fatigue life to crack initiation of the unwelded material is 10 times higher than the fatigue life of the butt-welded and unfinished material. The grinding of the butt-welds however leads to an increase of the fatigue life by a factor of 4 in comparison to the unfinished state. In comparison to these results obtained under 1 Hz the reduction of the frequency to 0.1 Hz causes a significant cyclic hardening and decrease of the fatigue life. The cold forming remains in all cases without influence. This hardening is a result of the diffusionless transformation of the austenitic microstructure into ferromagnetic α′-martensite under the lower frequency. The increase of the hardness caused also by the cold forming makes the stainless material more sensitive to corrosion.     

Diffusionsschweißen von Siliziumcarbid

Diffusion Bonding of Silicon Carbides Silicon carbide is a material that is suitable for high temperature application, especially for heat exchangers at high temperatures. Besides the problem of producing large components out of ceramics a technique for joining silicon carbide has to be developed. At high temperatures the joint has to be gastight und sufficient strength must be guaranteed. Diffusion bonding proved to be a good technique. The temperatures necessary for diffusion bonding are around 1200 °C, inert atmosphere or vacuum was used. The parameters of the procedures are discussed and correlated to strength, microstructure and permeability for gases.     

Ermüdungsverhalten von Schraubenverbindungen

Fatigue Behaviour of Bolted Connections In bolted connections the bolt must withstand under alternating forces the resulting fatigue loads at each local area. Therefore the endurance limit of the first stressed engaged thread in the nut or tapered hole is related to the thread diameter, the nut heigth and the strength ratio of the bolt and nut. It is shown which influence on the fatigue limit has the thread profile, the pitch-diameter-ratio, the prestress in relation to the strength grade of the bolt and the thread rolling process before or after heat treatment. Additional bending will cause a significant loss of fatigue strength, while high temperature application does not decrease the fatigue limit.     

Einfluß von unverformbaren Teilchen auf die Strangpresstexturen von Verbundwerkstoffen

Influence of undeformable particles on the extrusion texture of composite materials The influence of α-Al₂O₃ particles on the extrusion texture of Ni-, Cu or CuZn30-composites has been investigated, variing particle size and interparticles spacing. The rods show a 〈100〉-recrystallization texture, which decreases with greater values of the interparticle spacing. In the case of the addition-free Cu and CuZn30 a random orientation distribution of the crystals was found. These results are discussed in comparison with the results found on Al? Al₂O₃-composites.     

Ermüdungsverhalten von SiSiC

The Fatigue Behavior of SiSiC For design purposes the engineering property datas especially the fatigue behavior of silicon carbide (SiSiC) were determined. Using linear elastic fracture mechanics the datas for slip casted and extruded SiSiC-samples were measured at room temperature. The correlation between stress, probability of failure, and time is shown in SPT-diagrams.