1. Microstructure and surface topography study of nanolayered TiAlN/CrN hard coatingPeter Panjan, Peter Gselman, Matjaž Panjan, Tonica Bončina, Aljaž Drnovšek, Mihaela Albu, Miha Čekada, Franc Zupanič, 2022, izvirni znanstveni članek Opis: The microstructure and surface topography of PVD hard coatings are among the most
important properties, as they significantly determine their mechanical, tribological and other properties. In this study, we systematically analyzed the microstructure and topography of a TiAlN/CrN
nanolayer coating (NL-TiAlN/CrN), not only because such coatings possess better mechanical and
tribological properties than TiAlN and CrN monolayer coatings, mainly because the contours of the
individual layers, in the cross-sectional STEM or SEM images of such coatings, make it easier to
follow topographic and microstructural changes that occurred during its growth. We investigated
the effects of the substrate rotation modes on the microstructure and surface topography of the
NL-TiAlN/CrN coating, as well as on the periodicity of the nanolayer structure. The influence of the
substrate material and the ion etching methods were also studied, while special attention was given to
the interlayer roughness and influence of non-metallic inclusions in the steel substrates on the growth
of the coating. The topographical features of the NL-TiAlN/CrN coating surface are correlated with
the observations from the cross-sectional TEM and FIB analysis. Selected non-metallic inclusions,
covered by the NL-TiAlN/CrN coating, were prepared for SEM and STEM analyses by the focused
ion beam. The same inclusions were analyzed prior to and after deposition. We found that substrate
rotation modes substantially influence the microstructure, surface topography and periodicity of the
NL-TiAlN/CrN layer. Non-metallic inclusions in the substrates cause the formation of shallow craters
or protrusions, depending on their net removal rates during the substrate pretreatment (polishing
and ion etching), as compared to the matrix.
Ključne besede: magnetron sputtering, nanolayer hard coatings, growth defects, surface topography, interlayer roughness, non-metallic inclusion, focused ion beam (FIB), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM)
Objavljeno v DKUM: 19.03.2025; Ogledov: 0; Prenosov: 3
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2. Reduction of surface defects by optimization of casting speed using genetic programming : an industrial case studyMiha Kovačič, Uroš Župerl, Leo Gusel, Miran Brezočnik, 2023, izvirni znanstveni članek Opis: Štore Steel Ltd. produces more than 200 different types of steel with a continuous caster installed in 2016. Several defects, mostly related to thermomechanical behaviour in the mould, originate from the continuous casting process. The same casting speed of 1.6 m/min was used for all steel grades. In May 2023, a project was launched to adjust the casting speed according to the casting temperature. This adjustment included the steel grades with the highest number of surface defects and different carbon content: 16MnCrS5, C22, 30MnVS5, and 46MnVS5. For every 10 °C deviation from the prescribed casting temperature, the speed was changed by 0.02 m/min. During the 2-month period, the ratio of rolled bars with detected surface defects (inspected by an automatic control line) decreased for the mentioned steel grades. The decreases were from 11.27 % to 7.93 %, from 12.73 % to 4.11 %, from 16.28 % to 13.40 %, and from 25.52 % to 16.99 % for 16MnCrS5, C22, 30MnVS5, and 46MnVS5, respectively. Based on the collected chemical composition and casting parameters from these two months, models were obtained using linear regression and genetic programming. These models predict the ratio of rolled bars with detected surface defects and the length of detected surface defects. According to the modelling results, the ratio of rolled bars with detected surface defects and the length of detected surface defects could be minimally reduced by 14 % and 189 %, respectively, using casting speed adjustments. A similar result was achieved from July to November 2023 by adjusting the casting speed for the other 27 types of steel. The same was predicted with the already obtained models. Genetic programming outperformed linear regression.
Ključne besede: continuous casting of steel, surface defects, automatic control, machine learning, modelling, optimisation, prediction, linear regression, genetic programming
Objavljeno v DKUM: 25.03.2024; Ogledov: 284; Prenosov: 19
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3. Fingered core structure of nematic boojumsSamo Kralj, Riccardo Rosso, Epifanio Giovanni Virga, 2008, izvirni znanstveni članek Opis: Using the Landau-de Gennes phenomenological approach, we study the fine biaxial core structure of a boojum residing on the surface of a nematic liquid crystal phase. The core is formed by a negatively uniaxial finger, surrounded by a shell with maximal biaxiality. The characteristic finger's length and the shell's width are comparable to the biaxial correlation length. The finger tip is melted for topological reasons. Upon decreasing the surface anchoring strength below a critical value, the finger gradually leaves the bulk and it is expelled through the surface.
Ključne besede: physics, liquid crystals, nematic crystals, line defects, surface phenomena
Objavljeno v DKUM: 07.06.2012; Ogledov: 2110; Prenosov: 114
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