Band 59, Heft 5

Manganese Aluminum Bronze (MAB), UNS designation C95700, is an alloy widely used for large marine propellers and other components in hydropower units. MAB has a complex microstructure due to precipitation of intermetallic phases as consequence of the cast process or thermal treatments. When investigating the marine corrosion behavior of MAB alloys, it was found that a metallographic etching attack occurred under the effect of ultrasound, similar to that observed with chemical reagents used for high-alloy bronzes. The main aim of this work is to compare the effects of etching on polished metallographic samples by ultrasound in seawater with that obtained with conventional chemical agents. It can be concluded that the effect of ultrasound is able to reveal, with great precision, the microstructure of MAB alloys, without the use of aggressive chemical agents, while the time under the influence of ultrasonic energy allows for fine-tuning the etching effect.

Porosity represents one of the key parameters in the characterization of ceramic materials. Pores remaining after sintering often constitute the origin of direct mechanical or dielectric material failure. Isolated and large-scale pores in the microstructure are particularly problematic; many times these are larger than the average pore diameter. Their detection poses a particular challenge for analytics. The analytical methods used for ceramic materials either detects only part of the porosity or are greatly limited in view of area measurements. Moreover, the analysis of the morphology of detected pores is hardly possible or even impossible for the majority of methods. This research paper offers a detailed account of the qualitative analysis of porosity in oxide ceramics, with the primary focus being on possibilities for pore detection, the measured distribution functions, and the advantages of this method. This paper will show that the use of digital light microscopy together with coaxial illumination is capable of determining pore morphology and distribution in a fraction of time that would be required by conventional methods. The comparison of the measurement results, aided by well established methods for pore characterization, such as the linear intercept method (according to DIN EN ISO 13383), will enable a reliable validation of the results. Final FESEM analysis was used to enable a detailed study of the identified pores and to verify the results.

Large hot-rolled rings made of Alloy 718 were used as semi-finished product for turbomachinery components. Samples taken from one such ring exhibited non-uniform mechanical properties, partly below specified limits. Too high a volume fraction of delta phase in the microstructure was identified as the metallurgical root cause of failure. The case study presented in this contribution shows that such deviation from specified material properties does indeed constitute component failure, since the subject raw forging could not be used as is for fabrication of rotating equipment for gas turbine engines. To salvage the subject part and avoid having to scrap it at high cost, successful heat treatment tests were performed in the laboratory with the aim of eliminating delta phase to an extent, sufficient for property recovery. Heat treatment parameters were derived and recommended to the client. They were successfully applied before final machining and the subject hot-rolled ring was salvaged.

Optische Komponenten mit komplexen Geometrien wie Asphären, Linsen-Arrays oder Freiform-Optiken lassen sich durch Glasumformung effizient und kostengünstig fertigen. Das ständige Aufheizen, Umformen und Abkühlen führt allerdings dazu, dass die Umformwerkzeuge bereits nach wenigen Anwendungen stark verschleißen. Schutzbeschichtungen können die Lebensdauer der Werkzeugoberflächen verlängern. Das Fraunhofer-Institut für Produktionstechnologie IPT hat seinen Maschinenpark nun um eine Anlage zur Diamond-Like-Carbon-Beschichtung (DLC) erweitert und kann dami als einzige Einrichtung in Europa Forschungsarbeiten zu Beschichtungslösungen für alle Arten von Umformwerkzeugen und Glassorten anbieten.