Band 59, Heft 6

This study aims to develop a method for on-site metallography, enabling the characterization of carbide banding in cold-work steels via cellulose acetate film replication. It will be demonstrated that for this purpose, it is sufficient to grind the sample surface using P1500 mesh SiC abrasive paper and etch it with V 2 A etchant or nitric acid for 7 minutes. By sample preparation and etching, the matrix of the parent material is sufficiently removed for the carbides to leave a “negative” impression on the film. This negative replica can then be studied under reflected light microscope, enabling the characterization of carbide banding.

On the one hand, this work aims at describing the grain elongation of compressed samples of a microalloyed high-strength steel using appropriate parameters. On the other hand, the degree of recrystallization is to be determined based on the samples’ grain elongation. For this purpose, single-hit compression tests were performed with varying test parameter settings using a deformation dilatometer to generate samples characterized by various degrees of recrystallization. Three parameters were chosen to describe the grain elongation. It was found that the parameter defining the ratio length/ width of the original grain provides the highest sensitivity regarding changes in the grain elongation. Aiming at determining the degree of recrystallization, a critical grain elongation threshold value was determined below which it is assumed that a grain is recrystallized. The results show that choosing the right threshold value allows an automated determination of the degree of recrystallization of a microalloyed high-strength steel in the light microscope.

The case of damage presented here relates to the switching bridge of a medium voltage switch, a so-called make switch. Such assemblies are used for fast high current switching operations in medium voltage technology. The copper switching bridge failed due to low-cycle fatigue fractures symmetrically initiated where the transition radius between the copper bridge and the shaft was too sharp. The primary cause of the damage was the fact that the design principle of avoiding too sharp transition radii was needlessly violated where there were no apparent structural limitations. It is remarkable that, time and again, the violation of the same simple design rules causes component damages. The respective simple principles of good design practice thus violated are the same in virtually any mechanical engineering sector.

Wegen seiner herausragenden Transparenz sowie der Stabilität beim Kontakt mit Hitze oder Chemikalien ist Glas für viele Hightech-Anwendungen relevant. Herkömmliche Verfahren zur Formgebung von Glas sind aber oft langwierig, energieintensiv und stoßen bei kleinen und komplizierten Bauteilen schnell an ihre Grenzen. Die Freiburger Materialwissenschaftler Dr. Frederik Kotz-Helmer und Prof. Dr. Bastian E. Rapp haben in Kooperation mit der University of California in Berkeley/USA ein neuartiges Verfahren entwickelt, mit dem sich sehr kleine Bauteile aus transparentem Glas schnell und präzise per Mikro-3D-Druck herstellen lassen. Mögliche Anwendungen sind etwa Komponenten von Sensoren und Mikroskopen, aber auch von Lab-on-a-Chip-Systemen. Ihre Ergebnisse konnten die Forschenden in der aktuellen Ausgabe der renommierten Fachzeitschrift Science veröffentlichen.