Darja Steiner Petrovič

Core-Loss Prediction for Non-Oriented Electrical Steels Based on the Steinmetz Equation Using Fixed Coefficients With a Wide Frequency Range of Validity

An accurate prediction of the core losses is crucial for the optimal design and selection of the electrical steels used in electrical devices. The measured specific core losses are divided into three main parts, i.e., the eddy-current loss, the hysteresis loss, and the excess loss. In this paper, a simplified, predictive model for the core loss in a non-oriented electrical steel using fixed coefficients is proposed. The coefficients for a wide frequency spectrum up to 10 000 Hz of validity for the prediction of the eddy current, the hysteresis, and the excess components were calculated with respect to a sinusoidal voltage using the modified Steinmetz equation and a polynomial regression analysis.

The effect of cooling rate on the solidification and microstructure evolution in duplex stainless steel

The effects of the cooling rate on the solidification and microstructure evolution in the duplex stainless steel SAF 2205 was studied using DSC and light microscopy. A ferritoscope was used to measure the ferrite content. It was revealed that the cooling rate has an influence on the δ-ferrite nucleation temperature and the width of the solidification interval. Moreover, with an increase in cooling rate, the content of δ-ferrite increases, while the quantity of austenite in the ferrite matrix decreases and its morphology changes to acicular. A two-cycle DSC experiment made possible a more accurate interpretation of the collected data.

Microstructural Anisotropy of Magnetocaloric Gadolinium Cylinders: Effect on the Mechanical Properties of the Material

The development of advanced materials and technologies based on magnetocaloric Gd and its compounds requires an understanding of the dependency of mechanical properties on their underlying microstructure. Therefore, the aim of the study was to characterize microstructural inhomogeneities in the gadolinium that can be used in magnetocaloric refrigeration systems. Microstructures of magnetocaloric gadolinium cylinders were investigated by light microscopy and FE-SEM (Field Emission Scanning Electron Microscopy), EDS (Energy-dispersive X-ray Spectroscopy), and BSE (Back-scattered Electrons) in both the extrusion and the extrusion-transversal directions. XRD (X-ray Diffraction) analyses were performed to reveal the presence of calcium- and fluorine-based compounds. Metallographic characterization showed an oxidized and inhomogeneous microstructure of the cross-sections. The edges and the outer parts of the cylinders were oxidized more intensively on the surfaces directly exposed to the processing tools. Moreover, a significant morphological anisotropy of the non-metallic inclusions was observed. CaF inclusions act as active nucleation sites for internal oxidation. The non-metallic, Ca- and F-containing inclusions can be classified as complex calciumoxyfluorides. The solubility of Er and Yb in the CaF was negligible compared to the Gd matrix and/or the oxide phase. Lower mechanical properties of the material are a consequence of the lower structural integrity due to selective oxidation of surfaces and interfaces.