Band 61, Heft 9-10

The copper slate deposit of the Mansfeld copper mining area was mined in the 19 th and 20 th century. Mineral collectors can still find traces of copper smelting activities on the slag heaps of the various copper smelters. A piece from the Krug smelter slag heap mainly consists of Cu and Fe sulfides. The piece in question might be the intermediate product copper matte. The pieces from Hettstedt and the August Bebel smelter contain clearly visible metallic copper. The Hettstedt specimen might be a piece of furnace lining with adhering slag. Cr and Mg could be found, suggesting that chromium magnesia was used as refractory material. The piece from the August Bebel smelter contains up to 18 wt. % Cu. It does, however, not contain any sulfur. It is most likely Fe 2 SiO 4 slag (fayalite) with a high proportion of FeO. The presence of Sn and Zn suggests that this slag was formed during the processing of bronze or brass.

Despite advancements in metallography automation, sample preparation remains largely semi-automated with isolated subprocesses like sectioning, grinding, and polishing. Leveraging modern technologies such as collaborative robotics, AI-driven computer vision, and advanced sensors could enable fully integrated automation. However, the diversity of processes requires skilled human oversight. Integrating user-friendly cobot interfaces may promote a synergistic workspace that enhances safety, reduces monotony, and supports complex studies and documentation aligned with open science principles. Our study explores cost-effective mini robots in critical preparation stages, highlighting steps toward complex automation in metallography.

For the metastable austenitic steel AISI 347 (X6CrNiNb18-10), various electropolishing parameters were evaluated by means of hardness testing, electron backscatter diffraction (EBSD), and atomic force microscopy. Depending on the chosen parameters, different surface characteristics could be achieved simply by only varying voltage, flow rate, and polishing time, although EBSD indexing was always possible. Differences in hardness of up to 20 HV0.5 and in microscopic roughness could be detected on otherwise comparable samples. Finally, the microstructure distribution of a hot rolled bar material with a diameter of 153 mm made from AISI 347 was characterized over the cross section using the previously determined parameter set. Here, insights about recrystallization during forming were concluded and δ-ferrite was differentiated from α’-martensite by kernel average misorientation and morphology.

A partially destroyed burial ground from the Hallstatt period in the area of Mitterkirchen in Upper Austria was archaeologically investigated. The graves are dated to the Hallstatt C period corresponding to the 8 th /7 th century BC. Two triangular-headed nails and two lamellar “Buckel” (domed bronze plates) made of Sn-bronze were available for material investigations. One of each was subjected to metallographic examinations. The triangular-headed nail’s bronze contains about 15 wt. %Sn. The dendritic cast structure and the eutectoid phase Cu 41 Sn 11 are clearly visible. What is noticeable is that a Cu 41 Sn 11 layer formed in some areas of the surface. The lamellar Buckel’s microstructure is recrystallized and exhibits only a few deformation twins. Its bronze contains about 13 wt. %Sn. Hence, only very little Cu 41 Sn 11 is present. Elongated Cu 2 S precipitates indicate that the initial sheet was manufactured by fine forging.

In the field of materials analysis, chemical etching continues to play a crucial role in sample preparation, yet its approach is often more empirical. While classical metallographic methods dominate, insufficient understanding of the process creates room for innovation. To improve this situation, the development of new techniques allowing for structure observation during sample preparation is necessary. This is a critical step towards mitigating the influence of stochastic factors, thereby increasing the reliability and predictability of the outcomes. For real-time structural analysis during sample preparation, professional equipment was recently introduced. This contribution aims to verify in situ monitoring of structure during chemical etching using common laboratory equipment and a stereomicroscope with a camera and tablet. The method may encounter limitations due to the magnification and resolution capabilities of the stereomicroscope. Manipulation with a pipette and the risk of lens contamination with etchant can also be challenging. Additionally, etching in deeply dark etchants and ensuring adequate stirring of the etchant can be difficult. Nevertheless, this method offers new possibilities and can be beneficial for certain applications. To achieve a more comprehensive understanding, experiments with various materials and etchants are important to better grasp the limitations and possibilities of this innovative technique.

As climate change and resource scarcity intensify, the need for energy efficiency, emissions reduction, and resource conservation grows. Forming technology offers significant potential for light weighting, cost and resource efficiency. However, current component design often neglects forming-related damage, such as voids, focusing primarily on mechanical properties and safety factors. Integrating knowledge of these voids into the design process can improve efficiency and increase light weighting potential. Advanced scanning electron methods, such as electron contrast channeling imaging, evaluated forming-induced damage and correlated it with fatigue properties. Crack initiation occurred mainly near manganese sulfide inclusions or near-surface voids, influencing crack propagation. Analyzing void distribution using advanced secondary electron methods enabled the development of a 3D volume model.

Meteorites originate from the early phase of our solar system and are wonderfully undefined and inhomogeneous. In terms of its composition and microstructure, one single meteorite has quite a few surprises in store. The iron meteorite microstructure depends essentially on the initial solidification of the melt in a larger asteroid or minor planet. The solidification process itself is a function of local element concentrations and the very slow cooling rate. Various collisions in space resulted in the fragmentation of the asteroids and the deformation of the microstructure. However, whether visible microstructural changes occur or not depends on the microstructure itself. And finally, corrosion may also occur in the Earth’s atmosphere. An attempt is made to explain the different microstructures on the example of three iron meteorites, namely those found in Canyon Diablo, Gebel Kamil, and Dronino.

The Old Woman Meteorite (OWM), the second largest found in the USA, was located by prospectors in a steep canyon in the Mojave Desert about 20 km south of Highway 66 in March of 1976. Because of its weight of nearly 3 metric tons it had to be airlifted out of the mountains by a US Marine helicopter. A small triangular metallographic sample, on loan from the University of California Los Angeles, UCLA, was examined by light microscopy and energy dispersive X-ray spectroscopy (EDS) analysis to identify the structures and phases present. Rhabdites and schreibersite are visible in the as-polished condition. Nital etchant reveals grain boundaries and Neumann bands. Etching with Klemm I colors kamacite grains(ferrite) and Neumann bands in shades of blue and brown according to the crystal orientation. Prism shaped rhabdites stay white. Many rhabdites show cracks at the intersection with Neumann bands. Three areas with unusual structures were found. EDS dot maps identified one as schreibersite, another area contains troilite, schreibersite, brezinaite and possibly taenite, the third location contains Fe, Ni, P and S.

Owing to their specific property profile, titanium materials are particularly used in aerospace and medical technology applications. Highly β-stabilized titanium alloys are becoming more and more important for they can be strengthened by martensite decomposition and/or precipitation hardening, thus allowing the property profile to be adapted to the respective application. Not only α and β phase can occur in the respective alloys, but also the α’, α” or ω phase. The sample preparation is particularly problematic when high fractions of α” and β phase are present. They are characterized by a very low stiffness and strength, thus tending to form smear and deformation layers. Three examples will be quoted to describe the sample preparation of titanium materials with a high proportion of β-stabilizers (niobium, molybdenum, and tantalum) and various micrographs will be shown.

At the Central Institute for Engineering, electronics, and Analytics (ZEA-1 by its acronym in German) of the Jülich Research Center GmbH, a cryostat was developed for the European Spallation Neutron Source (ESS) and manufactured from a titanium-stabilized austenitic stainless steel alloy (EN 1.4571). After tungsten inert gas welding, the welds exhibited a black, patchy discoloration. After materialographic preparation, the phenomena were examined using microscopic methods to assess their impact on the strength of the weld and thus on the usability of the cryostat. Not only could the impact on the cryostat operation be assessed, but the formation mechanism could be elucidated and suitable measures could be outlined to avoid the black, patchy discoloration.

This project involved the metallographic examination of Early and Middle Bronze Age axes with respect to their manufacture and processing. The processing from casting to finished axe determines the microstructure and thus the properties required for use – in this case the combination of hardness and ductility – of the object. However, the objects under investigation are valuable cultural assets that must not be destroyed. For this reason, a preparation method was developed that allows the microstructures to be analyzed in a minimally invasive manner so that the objects can be restored. The investigations have shown that all objects have undergone a multi-stage thermomechanical treatment after casting, but to different degrees, resulting in different usability properties.

The 3D microstructure analysis presented in this study focuses on the nodular graphite of an EN-GJS grade cast iron. The shape is analyzed based on shape factor and aspect ratio as well as average particle size and distribution. The shape of graphites in cast iron materials is critical to the mechanical properties of these alloys and is essential for the characterization of the material. Metallographic serial sectioning creates a digital twin of the material, which is removed layer by layer and visualized layer by layer under an optical microscope. From this three-dimensional twin, any number of planes can be digitally projected and analyzed. Conventional quantitative 3D analysis examines the voxel count and composition of a body in 3D space. The analysis presented here applies stereological 2D analysis methods to three spatial planes of the material. Two of the planes are digital projections of the twin. The two reconstructed planes of the material are chosen so that the direction vectors of all three planes form an angle of 90° to each other. The methodology is described in detail and the challenges and opportunities of the serial section method presented here are discussed.

Due to a much lower nickel content, manganese aluminum bronzes (MAB) are a cost-effective alternative to nickel aluminum bronzes (NAB). When the material is processed, different microstructures are observable in the material which have an impact on the corrosion resistance of MAB alloys. MAB samples were annealed at 900 °C and quenched in water. After that, annealing treatments at 600, 500, 400 and 300 °C for up to 24 h were performed and the samples were again quenched in water. Metallographic sections were prepared from all samples and potentiostatic corrosion tests at different potentials were performed in synthetic seawater. It was found that the sample annealed at 900 °C and quenched in water as well as those samples which underwent a second annealing treatment at low temperatures for shorter times exhibited a greater corrosion tendency than those undergoing a second annealing treatment at higher temperatures. X-ray diffraction measurements revealed that phase transformations and changes in grain size occurred during the annealing treatments. The increase in corrosion resistance as a result of annealing at higher temperatures is probably due to the strong intergrowth of the phases that are formed.

X-ray computed tomography (XRT) is a nondestructive and thus reproducible examination method allowing the three-dimensional (3D) investigation of the internal and external structures of objects regardless of their material and geometry. In the present study, XRT was used to investigate the influence of hydrochloric acid leaching on the composition and constitution of iron-rich bauxite grains. Reducing the iron content in raw bauxites by acid leaching is a promising method for the beneficiation of iron-rich bauxites for subsequent use in the refractory industry. Not only the effect of the leaching process on the chemical composition of the bauxites, but also aspects such as the acid’s influence on the mineralogical composition and the resulting porosity of the individual grains have hardly been taken into account so far. To address these issues, various bauxites were examined before and after acid leaching using XRT analysis and specifically characterized with regard to their constitution.

Microstructural replicas are used in recurrent testing of hot, pressuriszed components to detect creep damage. The test location must be representative of the damage development and subsequent component failure. Poor preparation leads to the formation of artefacts which are considered in the damage assessment. The assessment is subject to method and operator variability. When assessing the life of components based on microstructure replicas, these must be taken into account and, if necessary, extended stress calculations for the component must be used.