Band 54, Heft 6

The connection between copper and art goes way back. For thousands of years, the ductile metal has been worked in cold state via hammer and punch to make jewelry, vessels or monuments. More recent examples are the Statue of Liberty in New York, the Quadriga in Berlin and the equestrian statue of Emperor William I at the Kyffhäuser. During the recently completed renovation of the Kyffhäuser monument it was possible to perform a scientific examination on the copper of the equestrian statue. The examinations showed that the material is multiphase due to the content of oxygen and lead. With regard to the mechanical properties, the impurity phases are only of little importance. Details of the microstructure with a spatially coherent order of impurity phases, however, have never been observed in this way. The formation of the microstructure is discussed taking into account the particular circumstances of the artistic shaping via repoussé and chasing.

Soft Magnetic Composites (SMC) consist of pure iron particles with an inorganic phosphorous coating and an additional iron oxide layer at the boundaries between them. It should be specified if the iron oxide is at the boundary of iron and the phosphorous coating or at the outer layer. It is assumed that it's a layer between the iron and the phosphorous layer. This combination of “ductile” and “brittle” constituents represents a challenge for preparing a specimen suitable for both microstructural and micromechanical studies. In particular for micromechanical tests, such as microcompression, microcantilever beam bending, micro tensile tests, and nanoindentation, the quality of the surface is critical. We demonstrate the effect of different surface preparation methods both on the microstructure and the mechanical properties. Mechanical polishing with two different end-polishing steps and combinations of mechanical polishing and ion-beam polishing are compared. Electron microscopy clearly showed the damaged or deformed surface layer of SMC specimens polished only mechanically, which significantly affected the mechanical properties as determined by nanoindentation. The microstructure of the particles was examined with electron backscatter diffraction and transmission electron microscopy revealing a subgrain structure within the particles. While the boundaries do not exhibit any cracks after indentation, the hardness of the boundaries and the adjacent material is clearly enhanced.

One of the main topics the working group “Quantitative Structural Analysis“ deals with is cast iron. The examination of metallographic 2D sections in order to eventually thus deduce the material properties of the three dimensional microstructure is common practice. Based on the results of a round robin test already performed in 2014, one of the then used samples was three-dimensionally measured in the IABG [1]. Using the thus obtained image data, a comparison between the 2D and 3D measurement results was performed in the second round robin test presented here. For the parameters graphite fraction and graphite size, a very good agreement could be achieved. However, there were important variations for the shape classification and the determination of the particle density. The main cause for this is the lack of appropriate specifications in the standard. Thus, the working group should further intensify the existing contact with the respective standardization bodies.

Again and again, components fail due to sudden crack initiation. In the present case, a hot-dip galvanized structural hollow section failed. It was manufactured from unalloyed structural steel of the type S355J0. Hydrogen plays a decisive role in this failure which results from a time-delayed damage of the material.