The surface segregation of copper was investigated in laboratory and industrial non-oriented electrical steel sheets containing copper. The cold-rolled samples of Fe-Si-Al alloys were annealed in the temperature range 320-1 120 K in the ultra-high-vacuum chamber of a field-emission Auger electron spectrometer, and subsequently characterized by Auger electron spectroscopy (AES). The Cu segregation rate was estimated based on the surface concentration of Cu after annealing at a given temperature. Not surprisingly, the AES analysis showed that the intensity of the surface segregation of copper increased with increasing annealing temperature. However, thermal desorption spectroscopy (TDS) showed that above 770 K the desorption of Cu started to reduce the surface concentration of Cu, thus making a reliable estimation of the segregation rate impossible. During the annealings, in addition to the surface segregation of copper, the surface segregation of alloying and impurity elements was observed as well. Moreover, it appeared that some of these constituents compete for available surface sites. For example, it could be concluded that the surface segregation of copper hindered the surface segregation of carbon in the Fe-Si-Al alloys.

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During routine metallographic investigations of some fully processed, non-oriented, electrical steel sheets, the typical MnS inclusions were not observed in the microstructures. In the MS-type sulphides, the manganese was substituted by magnesium. A systematic ex-situ characterisation of the non-metallic, magnesium-containing inclusions was carried out and the origin of the inclusions was proposed. The inclusions' chemistry and morphology were investigated by light microscopy and field-emission scanning electron microscopy. The non-metallic, magnesium-containing inclusions were classified as complex sulphides, oxides and spinels. Magnesium was also detected as being co-precipitated with other non-metallic inclusions, like nitrides. The form of the co-precipitated magnesium inclusions was predetermined by the shape of the thermodynamically most stable inclusions.KEY WORDS: magnesium; non-metallic inclusions; non-oriented electrical steel.

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Two binary biodegradable Mg-alloys and one ternary biodegradable Mg-alloy (Mg-0.3Ca, Mg-5Zn and Mg-5Zn-0.3Ca, all in wt%) were investigated. Surface-sensitive X-ray photoelectron spectroscopy analyses (XPS) of the alloy surfaces before and after immersion in simulated body fluid (SBF) were performed. The XPS analysis of the samples before the immersion in SBF revealed that the top layer of the alloy might have a non-homogeneous composition relative to the bulk. Degradation during the SBF immersion testing was monitored by measuring the evolution of H2. It was possible to evaluate the thickness of the sample degradation layers after the SBF immersion based on scanning electron microscopy (SEM) of the tilted sample. The thickness was in the order of 10–100 µm. The typical bio-corrosion products of all of the investigated alloys consisted of Mg, Ca, P and O, which suggests the formation of apatite (calcium phosphate hydroxide), magnesium hydrogen phosphate hydrate and magnesium hydroxide. The bioapplicability of the analyzed alloys with regard to surface composition and degradation kinetics is discussed.