Volume 50, Issue 6

In this paper, phases, chemical compositions and size of thermal oxides on an austenitic stainless steel AISI 316L were investigated. The steel specimens were subjected to isothermal heating at 200 °C up to 1000 °C in order to simulate production conditions and then compared with unheated specimens. X-ray diffraction analysis, Auger electron spectroscopy, Scanning electron microscopy and optical micrography have been used for characterization of the thermal oxides on the steel specimens.

The wear resistance of a series of Al-Si cast alloys with 5%, 8% and 11% silicon contents have been investigated after spheroidising heat treatments, and after coating these alloys by a plasma electrolytic oxidation (PEO) process for comparison. The alloys were subjected to wear tests by using SiC and steel counterfaces. The most remarkable observation is the increase in the wear resistance of the 5% Si containing alloy against SiC counterface, which is 70 times. However, the increase in the wear resistance is 5 times in the 11% Si containing alloy under same conditions, and only about 50% increase is observed when the counterface is steel. It is argued that, coating of these alloys by plasma electrolytic oxidation improves the wear resistance more effectively if the silicon content of the alloy is low, since the silicates (or aluminosilicates) in the coating layer has deleterious effect on wear resistance.

This contribution reports research concerning the wear behaviour of two thin hard coatings, diamond-like carbon (DLC) and chromium-nitride (CrN), deposited on substrate of different level of hardness. Prior to wear testing, all coatings were characterised with respect to their thickness, Young's modulus, hardness, and cohesion/adhesion. Afterwards, all samples were tested on particle erosion and abrasion. The particle erosion test shows a very low resistance of DLC coatings on that type of wear for all substrate hardnesses. CrN coating shows significantly better particle erosive wear resistence for very hard substrate than for soft. Abrasion tests have been performed by the use of two different methods: microscale abrasion, and dry sand/rubber wheel test under various normal loads. It was found that for the normal loads in range 0,1 N—1 N substrate hardness has no influence on the CrN lifetime, but for the higher normal loads 5 N—45 N hardness of the substrate strongly affects the CrN wear lifetime. DLC coating shows significant dependence on substrate hardness for all applied loads.

Over 90% of iron alloy castings are made in disposable moulds, i.e. in raw synthetic moulds. Raw mould mixture is applied in all production process types. Mould mixture is composed of sand as the basic component, binding material, water, and additives. Sand particles take up 70 to 95% of the total mould material in the mixture. The most frequently used sands include quartz sand, chromite sand, and olivine sand. Preliminary study of elution of foundry sand and mould mixture in distilled water has been studied through electrical conductivity measurements, complemented by measurements of the leaching concentrations of Cr 3 % , Al 3 % , Si 4 % , Ca 2 % , Mg 2 % , Fe 3 , and the pH value in eluates after the leaching process.

The study of chemical stability of ceramics in acid and alkalis makes it possible to predict their service properties in these media. For this reason, the chemical resistance of cold isostatically pressed (CIP) high-purity alumina ceramics (99.8% Al 2 O 3 ) was studied in different concentration of sulphuric acid (2 wt. %, 10 wt. % and 20 wt. %) at room temperature. Chemical stability was monitored by the determination of the amount of Al 3 % , Mg 2 % , Ca 2 % , Na % Si 4 % , and Fe 3 % ions eluted in different concentrations of sulphuric acid by means of atomic absorption spectrophotometry (AAS). The corrosion rate constants for CIP-alumina specimens after immersion in H 2 SO 4 solution using different concentrations were determined. Increasing the concentration from 2 to 20 wt. % it was notified that the corrosion susceptibility in H 2 SO 4 solutions for the CIP-alumina specimens at room temperature decreases.

Kurzfassung Mit dem Einsatz von Terahertz-Wellen eröffnen sich gegenüber Röntgenstrahlung neuartige Möglichkeiten der Radiologie. Von der dielektrischen Materialcharakterisierung nicht metallischer Werkstoffe bis zur Detektion des Innenlebens von unkonventionellen Spreng- und Brandvorrichtungen (USBV) wird ein großes Anwendungsspektrum für die bildgebende zerstörungsfreie Prüfung abgedeckt. Die physiologische Unbedenklichkeit der Strahlung favorisiert sie auch für Personenkontrollen an Flughäfen. Das Prinzip eines modernen zeitauflösenden Terahertz-Spektrometers mit einer Ortsauflösung bis 0,3 mm und einem Frequenzbereich von 0,1 bis 2,2 THz wird erläutert sowie die Wechselwirkung mit Materie. Die Besonderheiten von THz-Topogrammen werden am Beispiel einer Briefbombenattrappe mit Röntgen-Radiogrammen verglichen.

Kurzfassung Bei der Arbeit mit zivilen Sprengstoffen, wie etwa im Bergbau, in Steinbrüchen und bei Abbrucharbeiten, kommen elektrische Zünder zum Einsatz. Um deren Sicherheit und Zuverlässigkeit zu gewährleisten, werden die Baumuster neuer oder veränderter Zünder bei der Bundesanstalt für Materialforschung und Prüfung (BAM) getestet. Zu diesem Zweck realisierte die Berliner Ingenieurgesellschaft Aucoteam für die BAM einen intelligenten Zünderprüfplatz, der die mess- und gerätetechnischen Norm-Anforderungen automatisch berücksichtigt. An der Prüfeinrichtung können bis zu fünf Zünder gleichzeitig getestet werden, was den Einrichtungs- und Testaufwand erheblich reduziert.

Kurzfassung Eines der wichtigsten und am häufigsten angewendeten mechanisch-technologischen Prüfverfahren ist der Zugversuch. Die Normung dieses Prüfverfahrens hat eine lange Geschichte und befindet sich derzeit im Stadium der weltweiten einheitlichen Normung. Der vorliegende Beitrag vermittelt einen Überblick über die Entwicklung dieser Normen.