Iskanje po katalogu digitalne knjižnice

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: 0
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Ključne besede: aluminijeve zlitine, toplotna obdelava, mikrostruktura, disperzoidi, dilatometrija, trdota, aluminium alloy, heat treatment, microstructure, dispersoids, dilatometry, DSC, hardness
Objavljeno v DKUM: 05.04.2024; Ogledov: 183; Prenosov: 21
Celotno besedilo (11,03 MB)
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Opis: The plate heat exchanger (PHE) is a component that provides heat to be transferred from hot water to domestic cold water without mixing them with high efficiency. Over the lifetime of the PHE, cyclic pressures act on the brazing points and the plates, and this may lead to fatigue failure. The fatigue behaviour of the PHE, designed using copper-brazed 316L stainless steel, was investigated in this study. First, the fatigue tests under the load ratio R = 0.1 were performed on the Vibrophore 100 testing machine to obtain the S-N curve of the analysed brazed joint. Based on the obtained experimental results, an appropriate material model of the analysed brazed joint has been created, which was validated with numerical calculation in the framework of a program code Ansys. A validated material model was then used for the subsequent numerical analysis of PHE. In order to carry out a numerical calculation using the finite element method (FEM), a three-dimensional model of the heat exchanger was created based on the previous scanning of PHE-geometry. Thereafter, the geometry was parameterised, which allowed us to perform parametric simulations (monitoring different responses depending on the input geometry). Numerical simulations were carried out in the framework of the Ansys 2023-R1 software, whereby the obtained results were analysed, and the responses were appropriately characterised according to previously determined load cases.
Ključne besede: brazed joint, fatigue, experimental testing, computational analyses, heat exchanger
Objavljeno v DKUM: 31.01.2024; Ogledov: 316; Prenosov: 62
Celotno besedilo (7,44 MB)
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Opis: A comprehensive experimental investigation of the wear behaviour of coated spur polymer gears made of POM is performed in this study. Three different thicknesses of aluminium (Al) coatings were investigated and deposited by the Physical Vapour Deposition (PVD) process. The Al coating was deposited in three steps: By plasma activation, metallisation of the aluminium by the magnetron sputtering process, and plasma polymerisation. The wear of the gears was tested on an in-house developed testing rig for different torques (16, 20, and 24 Nm) and a rotational speed of 1000 rpm. The duration of the experiments was set to 13 h, when the tooth thickness and, consequently, the wear of the tooth flank were recorded. The experimental results showed that the influence of metallisation with aluminium surface coatings on the wear behaviour of the analysed polymer gear is not significantly important. The results also showed that the gears with a thicker aluminium coating showed greater wear than gears with a thinner coating or even without a coating. This is probably due to the fact that the aluminium particles that started to deviate during gear operation represented the abrasive material, which led to the faster wear of the contacting surfaces of the meshing gear flanks.
Ključne besede: polymer gears, aluminium PVD coating, Physical Vapour Deposition process, multilayer coating, wear
Objavljeno v DKUM: 15.11.2022; Ogledov: 580; Prenosov: 83
Celotno besedilo (13,01 MB)
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Opis: In this study the effect of the cooling rate on the microstructure of Al94 Mn2 Be2 Cu2 alloy was investigated. The vacuum induction melted and cast alloy was exposed to different cooling rates. The slowest cooling rate was achieved by the DSC (10 K·min^−1), the moderate cooling rate succeeded by casting in the copper mould (≈1 000 K·s−1) and the rapid solidification was performed by melt spinning (up to 10^6 K·s^−1). The microstructure of the DSC-sample consisted of α-Al matrix, and several intermetallics: τ1-Al29 Mn6 Cu4 , Al4 Mn, θ-Al2 Cu and Be4 Al(Mn,Cu). The microstructures of the alloy at moderate and rapid cooling consisted of the α-Al matrix, i-phase and θ-Al2 Cu. Particles of i-phase and θ-Al2 Cu were much smaller and more uniformly distributed in melt-spun ribbons.
Ključne besede: Al-alloy, metallography, microstructure, cooling rate, solidification
Objavljeno v DKUM: 03.07.2017; Ogledov: 1019; Prenosov: 104
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