Monika Jenko

Vacuum sintering of water-atomised HSS powders with MoS2 additions

Molybdenum disulphide (MoS 2 ) is a well-known and widely used solid lubricant. As such, it might also be a useful addition in the production of composite self-lubricating high-speed steel parts which are used in different anti-wear applications. MoS 2 might also have a favourable influence on the synthesis of sintered HSS. In view of this, the compressibility and the sinterability of M3/2 and M35 types of HSS powder mixtures with MoS 2 additions were investigated. In this paper, the influence of MoS 2 on the densification during vacuum sintering of selected HSSs is presented. It has been established that the densification of HSS-MoS 2 powder mixture proceeds by a combination of a reactive and super-solidus liquid-phase sintering process. The added MoS 2 reacts with the steel matrix, enhancing densification. Complex sulphides (Cr, V, Fe)S are formed, whilst the Mo enriches the steel matrix and forms complex carbides with other alloying elements.

Carbon-containing Ti–C:H and Cr–C:H PVD hard coatings

Abstract Ti–C:H and Cr–C:H coatings were prepared by reactive sputtering in a Balzers Sputron deposition system at a substrate temperature of approximately 150°C. Acetylene was used as reactive gas. Coatings were deposited onto polished tool steel and silicon substrates. Transmission electron microscopy, Auger electron spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, scratch test and microindentation were used to characterize the properties of the coatings.

HRAES study of oxide scale formation by decarburization of non-oriented electrical steel sheets

Abstract The oxide growth during the decarburization process of non-oriented silicon steel sheets alloyed with 0.5 and 1 mass% of aluminium was studied using high-resolution auger electron spectroscopy (HRAES), the chemical composition was characterized by X-ray photoelectron spectroscopy (XPS). The samples were annealed in a H 2 –H 2 O–N 2 gas mixture with different oxygen potential in the temperature range from 800 to 1050°C. We found that oxide scale was a mixture of FeO, Fe 3 O 4 and SiO 2 and Fayalite (FeSi 2 O 4 ). This oxide scale was porous. In the high Al alloyed sheets (2 mass% Si and 1 mass% Al) the oxide scale was a mixture of FeO, Fe 3 O 4 , and Al 2 O 3 and also Hercynite (Fe Al 2 O 4 ). In this case the oxide scale was compact. For thermodynamic calculations of Fayalite and Hercynite formation during the decarburization process the Gibbs energy minimization model (GPRO) was applied (Korousic, Kovine zlitine tehnol 1994;28:609; Korousic and Rosina, RadexRundsch 1994;1(2):523).

Orientation-dependent ion beam sputtering at normal incidence conditions in FeSiAl alloy

The authors have performed Ar+ broad ion beam sputtering of a polycrystalline Fe–Si–Al alloy at normal incidence at energies varying from 6 to 10 keV. Sputtering results in the formation of etch pits, which can be classified in three shapes: triangular, rectangular, and square. As each grain of individual orientation exhibits a certain type of pattern, the etch pits were correlated with the crystal orientations by electron backscattered diffraction technique.

A HRAES study of the morphology of non-metallic inclusions in non-oriented electrical steel containing Cu and Se

Abstract Electrical steel sheets are mainly produced from Fe–Si–C alloys. Non-oriented electrical steels contain, in addition to the important alloying elements Si, Al and Mn, other elements that determine the characteristics of the electrical steel. Al and Mn form the non-metallic inclusions AlN and MnS, which inhibit secondary recrystallization in the steel sheets. This influences both the texture development and the magnetic properties. The aim of this study was to analyze the morphology of the non-metallic inclusions in the non-oriented electrical steel sheet containing copper and selenium additions. The Fe–Si–Al alloy was produced in a laboratory vacuum-induction furnace, hot formed and then finally cold formed into a steel sheet. To achieve the optimum magnetic properties the steel sheet was decarburized in a H2/H2O gas mixture. The morphology of the non-metallic inclusions in the steel sheet prior to, and after, decarburization annealing at 840°C and their modification by the addition of the alloying elements Cu and Se were investigated using HRAES.

Effect of tempering on the chemical and phase composition of MxCy precipitates in low carbon chromium-molybdenum-vanadium steel

Abstract The evolution of the chemical and phase composition of carbide precipitates in X20CrMoV12.1 steel after long-term service of 56000 h (470–530 °C at up to 18 MPa) and after heat treatment (650 and 800 °C) was investigated using transmission electron microscopy and Auger electron spectroscopy. The precipitates found were mostly of M23C6 type, the S- and χ-phase and traces of M2C. In service loaded state the presence of M7C3 precipitates was also established. The evolution sequence is obviously M3C → M7C3 → M23C6.

Surface segregation of antimony in Fe-Si steel for grain oriented sheets

Abstract Surface segregation of antimony in a polycrystalline Fe-Si alloy with 0.049 wt% Sb was investigated by Auger electron spectroscopy in the temperature range from 450 to 800°C, and the segregation kinetics of antimony were described. From the surface segregation kinetics and its temperature dependence the bulk diffusion coefficient of antimony and the activation energy were determined in the temperature range from 500 to 600°C.

Surface characteristics of isopod digestive gland epithelium studied by SEM

The structure of the digestive gland epithelium of a terrestrial isopod Porcellio scaber has been investigated by conventional scanning electron microscopy (SEM), focused ion beam–scanning electron microscopy (FIB/SEM), and light microscopy in order to provide evidence on morphology of the gland epithelial surface in animals from a stock culture. We investigated the shape of cells, extrusion of lipid droplets, shape and distribution of microvilli, and the presence of bacteria on the cell surface. A total of 22 animals were investigated and we found some variability in the appearance of the gland epithelial surface. Seventeen of the animals had dome-shaped digestive gland “normal” epithelial cells, which were densely and homogeneously covered by microvilli and varying proportions of which extruded lipid droplets. On the surface of microvilli we routinely observed sparsely distributed bacteria of different shapes. Five of the 22 animals had “abnormal” epithelial cells with a significantly altered shape. In three of these animals, the cells were much smaller, partly or completely flat or sometimes pyramid-like. A thick layer of bacteria was detected on the microvillous border, and in places, the shape and size of microvilli were altered. In two animals, hypertrophic cells containing large vacuoles were observed indicating a characteristic intracellular infection. The potential of SEM in morphological investigations of epithelial surfaces is discussed.

Texture measurements on electrical steels alloyed with tin

Based on texture measurements it has been proved that small additions of Sn to electrical steel during recrystallization promotes the growth of grains with favourable orientations. The grain boundary, intercrystalline and surface segregation of tin were investigated using Auger electron spectroscopy (AES) and the textures of recrystallized cold-rolled electrical steels were measured by a computer-controlled texture diffractometer.

Scanning tunneling microscopy study of Sb-alloyed electrical steel sheet

Abstract Scanning tunneling microscopy (STM) was used to study the surface of the 0.1% Sb alloyed electrical steel sheet. Material was subjected to thermal treatment to induce the surface segregation of impurities as well as alloying component. It was found that Fe–S compound formed on the surface. This was determined by direct observation of the compounds unit cell. Additional support was found in thermodynamical arguments and measurements of surface segregation temperature dependence by AES.