Volume 55, Issue 3

Copper is a material used in a wide range of applications. The combination of electrical conductivity and mechanical strength is a feature which is especially important when it comes to conductive and contact materials. This combination of properties in low-alloy copper-based alloys can be achieved when the material is subjected to a thermomechanical treatment consisting of rolling and annealing. Samples of the alloy CuNi1.5Si0.3 were taken at distinctive steps of the industrial manufacturing process for semi-finished products in order to examine the influence of the manufacturing parameters on the microstructure during solution annealing, rolling, and aging. The sample material for the respective chosen conditions was aged in the laboratory at various temperatures. Quasi-static tensile tests were performed, the electrical conductivity was determined, the microhardness was measured, and the microstructure was examined on metallographic sections in order to characterize the material conditions.

This article describes stochastic 3D structure models for electrodes of lithium-ion batteries, which can be used for model-based optimization of the electrode morphology. First, a single particle model is presented which can be used to parametrically describe individual particles from 3D tomographic image data. By fitting parametrical distributions it is therefore also possible to simulate (statistically similar) particles. Hereafter, different approaches for the arrangement of individual particles in the observation window are presented, so that system-based properties of different electrode types can be approximately matched (e. g. the connectivity of the particle system as well as the structure of the pore space). Finally, algorithms for the automatic recognition of particle cracks in tomographic image data are presented which can be used to integrate ageing effects into the models.

This work aimed at performing a more in-depth analysis of the influence of the tempering temperature on the microstructure development in carbonitrided case-hardening steels. To this end, X-ray measurements are performed alongside various metallographic methods. It was, above all, due to the unusually high tempering temperature of 280 °C for case-hardened samples that the conventional characterization methods initially did not yield satisfying results. Therefore, examinations in the scanning and the transmission electron microscope as well as EBSD investigations were performed alongside the light microscopy analyses. The motivation for the examinations was and is the challenge or rather the desire to gain better understanding of the correlation between load capacity results and the respective surface layer microstructures.

The slotted center guide bolt of the center guide feature of the lower part of the outer shell of an annular combustion chamber was found fractured in a heavy-duty gas turbine engine used for power generation, after approximately 5.500 operating hours. The incident was a one-off event and not a recurring incident. No similar events were reported from the fleet; hence the failure was not considered a field issue. The metallurgical root cause investigation that was ordered to determine the failure mechanism revealed that the incident center guide bolt failed by fretting fatigue cracking, a high cycle fatigue (HCF) phenomenon.