Articles (KMM)

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Investigation of the Effect of pH on Stress Corrosion Cracking of API 5L X65 Steel by Impedance Spectroscopy and Slow Strain Rate Tensile Test
(2021) Hassanzadeh, Soheila; Danaee, Iman; Saebnoori, Ehsan; Chocholatý, Ondřej; Kříž, Antonín; Eskandari, Hadi
In this study, impedance spectroscopy, slow strain rate tensile test, and scanning electron microscopy were used to investigate the susceptibility of API 5L X65 steel to stress corrosion cracking (SCC) in a sulfide brine solution with different pHs. According to the analysis of SSRT, steel was susceptible to SCC in a brine solution. The reduction area ratio in the air was measured to be 80.3%, which was more significant than the reduction obtained in a brine solution with different pHs. EIS in different strain time in acidic solution exhibited an inductive element, which indicated strong hydrogen penetration effects and sulfide stress cracking (SSC) of steel in this environment. EIS in neutral and basic brine solutions presented constant phase element behavior of the porous electrodes, which indicated SCC behavior of steel in these solutions. Phase angle analysis indicated that cracks grow considerably after 9 h. Additionally, SEM illustrated a ductile type of fracture in the air and brittle type of fracture in all brine solutions. At low pH, internal cracks showing the interaction of hydrogen embrittlement and SSC before fracture were detected. At medium and high pHs, SEM exhibited many secondary cracks perpendicular to the tensile load, indicating the SCC behavior of X65 steel in these media.
Structure and Properties of TiO2/nanoTiO2 Bimodal Coatings Obtained by a Hybrid PVD/ALD Method on 316L Steel Substrate
(2021) Staszuk, Marcin; Pakula, Daniel; Reimann, Lukasz; Kloc-Ptaszna, Anna; Pawlyta, Miroslawa; Kříž, Antonín
This paper presents the synergy of the effect of two surface engineering technologies-magnetron sputtering (MS-PVD) and atomic layer deposition (ALD) on the structure and properties of 316L steel. Recent studies indicate that PVD coatings, despite their thickness of a few micrometers, have many discontinuities and structural defects, which may lead to pitting corrosion after time. Applying an ALD layer to a PVD coating seals its structure and contributes to extending the service life of the coating. Investigations of the structure and morphology of the produced layers were carried out using a scanning electron microscope (SEM) and atomic force microscope (AFM). In addition, the structure of the coatings was investigated on the cross-section using a scanning-transmission electron microscope S/TEM. The tribological properties of the materials studied were determined by the ball-on-disc method. The corrosion resistance of the tested materials was determined by the electrochemical potentiodynamic method by recording the polarization curves of the anodes. Additional information about the electrochemical properties of the tested samples, including the quality, their tightness, and their resistivity, was obtained by electrochemical impedance spectroscopy (EIS). In addition, the main mechanisms of corrosion and tribological wear were determined by SEM observations after corrosion tests and after tribological tests. The study showed that the fabrication of hybrid layers by MS-PVD and ALD techniques allows obtaining coatings with electrochemical properties superior to those of layers fabricated by only one method.
Impact of rotor material wear on the aluminum refining process
(2022) Prášil, Tomáš; Socha, Ladislav; Gryc, Karel; Sviželová, Jana; Saternus, Mariola; Merder, Tomazs; Pieprzyca, Jacek; Gráf, Martin
The paper presents the results of tests carried out during the refining of the AlSi9Cu3(Fe) alloy in industrial conditions at the FDU stand. In the tests, three different rotors made of classical graphite, fine-grained graphite and classical graphite with SiC spraying were tested for the degree of wear. A series of tests was conducted for five cases—0% to 100% of consumption every 25%—corresponding to the cycles of the refining process. The number of cycles corresponding to 100% wear of each rotor was determined as 1112. The results of the rotor wear profile for all types of graphite after the assumed cycles are presented. Comparison of CAD models of new rotors and 3D scans of rotors in the final stage of operation revealed material losses during operational tests. The study assessed the efficiency of the rotor in terms of its service life as well as work efficiency. It was estimated on the basis of the calculated values of the Dichte Index (DI) and the density of the samples solidified in the vacuum. The structure of samples before and after refining at various stages of rotor wear is also presented, and the results are discussed.
Investigations of TiO2, Ti/TiO2 and Ti/TiO2/Ti/TiO2 coatings produced by ALD and PVD methods on Mg-(Li)-Al-RE alloy substrates
(2021) Staszuk, Marcin; Reimann, Lukasz; SciSlak, Aleksandra; Jaworska, Justyna; Pawlyta, Miroslawa; Mikuszewski, Tomasz; Kuc, Dariusz; Tanski, Tomasz; Kříž, Antonín
Magnesium alloys have recently become increasingly popular in many sectors of the industry due to their unique properties, such as low density, high specific strength, vibration damping ability along with their recyclability and excellent machinability. Nowadays, thin films have been attracting more attention in applications that improve mechanical and corrosion properties. The following alloys were used for the coated Mg-Al-RE and the ultra-light magnesium-lithium alloy of the Mg-Li-Al-RE type. A single layer of TiO2 was deposited using the atomic layer deposition ALD method. Multiple layers of the Ti/TiO2 and Ti/TiO2/Ti/TiO2 type were obtained by the MS-PVD magnetron sputtering technique. Samples were investigated by scanning and a transmission electron microscope (SEM, TEM) and their morphology was studied by an atomic forces microscope (AFM). Further examinations, including electrochemical corrosion, roughness and tribology, were also carried out. As a result of the research, it was found that the best electrochemical properties are exhibited by single TiO2 layers obtained by the ALD method. Moreover, it was found that the Ti/TiO2/Ti/TiO2 double film has better properties than the Ti/TiO2 film.
Effect of initial microstructure on hot deformation behavior of AlMg5Si2Mn alloy
(2021) Snopinski, Przemyslaw; Krol, Mariusz; Tanski, Tomasz; Pakula, Daniel; Kříž, Antonín
In this study, the hot deformation behavior of high-temperature annealed and as-cast AlMg5Si2Mn aluminum alloy was investigated in compression tests carried out between 350 and 430 degrees C, with a strain rate of 0.005-0.5 s(-1), using a DIL 805A/D quenching-deformation dilatometer equipped with an accessory that allowed hot compression tests to be performed in either a vacuum or an inert gas atmosphere. To reveal the mechanism of hot deformation, the flow stress behavior and microstructural evolution were investigated after the hot compression tests. Constitutive constants for the as-cast and annealed state were then calculated and compared. The results show that the alloy in the annealed state exhibited lower deformation resistance under the same deformation conditions, especially at low deformation temperatures. The activation energies for deformation, Q, for the as-cast and annealed conditions were calculated to be 181 kJ*mol(-1) and 169 kJ*mol(-1), respectively.
Impedance Studies on Stress Corrosion Cracking Behavior of Steel Pipeline in NS4 Solution under SSRT Test Condition
(2021) Ghobadi, Moslem; Danaee, Iman; Saebnoori, Ehsan; Eskandari, Hadi
Stress corrosion cracking behavior of API 5L X65 steel in a NS4 solution with different pH was investigated by electrochemical impedance under slow strain rate tensile test. NS4 solution was selected as corrosive electrolyte under disbonded pipeline coatings. According to the analysis of tensile test, steel was susceptible to SCC in a NS4 solution. The reduction area ratio in the air was measured to be 70.71%, which was more significant than the reduction obtained in a NS4 solution with different pH. EIS in different strain time in acidic solution showed perfect semicircles, which indicated high dissolution rate and some hydrogen penetration effect in this environment. EIS in neutral and basic NS4 solution presented effective constant phase elements in the transmission line model for the porous electrode, which indicated SCC behavior of steel in these solutions. Phase angle analysis indicated that cracks grow considerably after 12 h. Besides, SEM illustrated a ductile type of fracture in air and brittle type of fracture in all NS4 solution.
Aluminum melt degassing process evaluation depending on the design and the degree of the FDU unit graphite rotor wear
(2022) Podařil, Martin; Prášil, Tomáš; Majerník, Ján; Kampf, Rudolf; Socha, Ladislav; Gryc, Karel; Gráf, Martin
One of the most important indicators of casting quality is porosity. The formation of pores is largely conditioned by the presence of hydrogen in the batch and subsequently in the melt. The gasification of the melt is the primary factor increasing the porosity of casts. This paper addresses the issue of reducing the melt gasification by using FDU (Foundry Degassing Unit) unit. The gas content in the melt is evaluated by determining the Dichte Index depending on the geometry and the degree of the FDU unit rotor wear. For experiments performed under the operating conditions, three types of graphite rotors with different geometries are used. The extent of melt gasification and the Dichte Index are monitored during the rotor wear, at a rate of 0%, 25%, 50%, 75% and 100% rotor wear. Secondly, the chemical composition of the melt is monitored depending on the design and wear of the rotor. It is proven that the design and the degree of rotor wear do not have significant effect on the chemical composition of the melt and all evaluated samples fell within the prescribed quality in accordance with EN 1706. With regard to the overall comparison of the geometry and wear of individual rotor types, it has been proven that, in terms of efficiency, the individual rotors are mutually equivalent and meet the requirements for melt degassing throughout the service life.
Novel High-Entropy Aluminide-Silicide Alloy
(2021) Novák, Pavel; Nová, Kateřina
Novel high-entropy (multi-principal elements) alloy based on Fe-Al-Si-Ni-Ti in equimolar proportions has been developed. The alloy powder obtained by mechanical alloying is composed of orthorhombic FeTiSi phase with the admixture of B2 FeAl. During spark plasma sintering of this powder, the FeSi phase is formed and the amount of FeAl phase increases at the expense of the FeTiSi phase. The material is characterized by a high compressive strength (approx. 1500 MPa) at room temperature, being brittle. At 800 degrees C, the alloy is plastically deformable, having a yield strength of 459 MPa. The wear resistance of the material is very good, comparable to the tool steel. During the wear test, the spallation of the FeSi particles from the wear track was observed locally.
Wear Resistance of (Ti,Al)N Metallic Coatings for Extremal Working Conditions
(2021) Mikula, Jaroslaw; Pakula, Daniel; Zukowska, Ludwina; Golombek, Klaudiusz; Kříž, Antonín
The article includes research results for the functional properties achieved for a wide range of sintered tool materials, including sintered carbides, cermets and three types of Al2O3 oxide tool ceramics ((Al2O3 + ZrO2, Al2O3 + TiC and Al2O3 + SiC(w)) with (Ti,Al)N coating deposited in the cathodic arc evaporation (CAE-PVD) method and comparison with uncoated tool materials. For all coated samples, a uniform wear pattern on tool shank was observed during metallographic analysis. Based on the scanning electron microscope (SEM) metallographic analysis, it was found that the most common types of tribological defects identified in tested materials are: mechanical defects and abrasive wear of the tool side, crater formation on the tool face, cracks on the tool side, chipping on the cutting edge and built-up edge from chip fragments. Deposition of (Ti,Al)N coating on all tested substrates increases the wear resistance and also limits the exceeding of critical levels of permanent stresses. It even increases the tool life many times over. Such a significant increase in tool life results, among other things, from a large increase in microhardness of PVD coated materials compared to uncoated samples, increased resistance to thermal and chemical abrasion, improved chip formation and removal process conditions. Use of hard coatings applied to sintered tool materials is considered to be one of the most important achievements in improving the functional properties of cutting tools and can still be developed by improving the coating structure solutions (sorted and nanocrystalline structures) and extending the range of coating applications (Ti,Al)N in a variety of substrates.
Comparison of degassing efficiency on a foundry degassing unit using different rotor types
(2024) Kolínský, Jan; Prášil, Tomáš; Socha, Ladislav; Sviželová, Jana; Gryc, Karel; Häusler, Josef; Dvořák, Martin
The present paper describes a comparison of the efficiency of different types of rotors used in the refining of aluminium melt at a foundry degassing unit (FDU). Physical modelling was used to obtain data for six different rotor types under defined experimental conditions. In order to evaluate the data from the physical model, an evaluation method based on the interpolation of degassing curves was developed in such a way that the resulting characteristic can be expressed by a single parameter. Using the new methodology, the datasets were replaced by a single dimensionless parameter, a, which characterizes the rotor performance at a given gas flow rate. Based on the comparison of these performance parameters, it was possible to mutually compare the rotor efficiency depending on the selected conditions. The comparison is also demonstrated on the expected degassing time to a certain required concentration. Based on the physical model results, the study found that rotor D had the highest degassing efficiency, followed by rotors F and A. Rotors B and E had similar efficiency at a flow rate of 17 Nl·min−1. However, rotor B showed better efficiency at higher inert gas flow rates (19 and 21 Nl·min−1), while rotor E showed better efficiency at lower flow rates (13 and 15 Nl·min−1).
Effect of Q-P process parameters on the microstructure and mechanical properties of SECURE 400 steel
(2024) Coufal, Vladislav; Kučerová, Ludmila; Jeníček, Štěpán; Leták, Radek; Jirková, Hana
SECURE 400 steel is used for basic ballistic protection of armoured vehicle chassis against the pressure energy of exploding mines, IEDs and grenades. It is a low-alloy high- strength steel with a manufacturer's declared hardness of 380 to 430 HB, which is characterized by a good combination of high strength and toughness. As standard, this steel is processed by quenching followed by tempering, but new possibilities for improving its mechanical properties are constantly being sought. A modern heat treatment process, the so-called Q-P process, leads to the formation of a multiphase structure, which positively influences the mechanical properties. Therefore, this paper focuses on describing the influence of Q-P process parameters on the development of the microstructure and mechanical properties. During the experimental program, it was found that the Q-P process increased the ultimate tensile strength by up to 300 MPa and increased the hardness by up to 68 HV10 compared to the post-delivery condition where tensile strength and hardness values of 1354 MPa and 438 HV10, corresponding to 414 HB, were measured. Redistribution of the carbon from the supersaturated martensite stabilised the austenite and a finer grained microstructure was achieved.
Lasery ve strojírenství
(2024) Němeček, Stanislav
Před 20 lety vstoupily na komerční trh moderní vláknové, diskové a diodové lasery s výkonem nad jeden kilowatt, tedy nástroje použitelné ve strojírenské výrobě. To se projevilo v řadě současných technologií, od svařování přes povrchové úpravy až k aditivní výrobě.
Using physical modeling to optimize the aluminium refining process
(2022) Prášil, Tomáš; Socha, Ladislav; Gryc, Karel; Sviželová, Jana; Saternus, Mariola; Merder, Tomasz; Pieprzyca, Jacek; Gráf, Martin
Concern for the environment and rational management of resources requires the development of recoverable methods of obtaining metallic materials. This also applies to the production of aluminium and its alloys. The quality requirements of the market drive aluminium producers to use effective refining methods, and one of the most commonly used is blowing an inert gas into liquid aluminium via a rotating impeller. The efficiency and cost of this treatment depends largely on the application of the correct ratios between the basic parameters of the process, which are the flow rate of the inert gas, the speed of the rotor and the duration of the process. Determining these ratios in production conditions is expensive and difficult. This article presents the results of research aimed at determining the optimal ratio of the inert gas flow rate to the rotary impeller speed, using physical modeling techniques for the rotor as used in industrial conditions. The tests were carried out for rotary impeller speeds from 150 to 550 rpm and gas flow rates of 12, 17 and 22 dm3/min. The research was carried out on a 1:1 scale physical model, and the results, in the form of visualization of the degree of gas-bubble dispersion, were assessed on the basis of the five typical dispersion patterns. The removal of oxygen from water was carried out analogously to the process of removing hydrogen from aluminium. The curves of the rate of oxygen removal from the model liquid were determined, showing the course of oxygen reduction during refining with the same inert gas flows and rotor speeds mentioned above.
Impact of rotor design on its wear and work efficiency of the aluminum refining process
(2022) Prášil, Tomáš; Socha, Ladislav; Gryc, Karel; Sviželová, Jana; Saternus, Mariola; Merder, Tomazs; Pieprzyca, Jacek; Gráf, Martin
Both the wear and the geometry of the rotor determine the efficiency of the process of aluminum refining. The paper presents wear tests of two different rotors: I (pump type) and II (propeller type). The operation of both rotors in industrial conditions was compared and their service life was examined. It was found that rotor I is more durable than the tested rotor II, and at the same time it provides a good level of hydrogen removal throughout the operation period, i.e., 1112 refining cycles. Rotor wear after refining was calculated by 3D scanning. The study also investigated the impact of rotor geometry on the efficiency of the refining process. The degassing efficiency was determined during refining in a foundry using the Dichte Index (DI). The alloy density and the volume of hydrogen removed were also tested for five stages of rotor wear: 0%, 25%, 50%, 75% and 100%. Both new rotors performed worse in removing hydrogen from the liquid alloy than the worn rotors due to their humidity which cannot be eliminated in the initial stage of their operation. A Dross Test was also performed to determine non-metallic impurities and compare size and number of cavities for rotor I and II. The best results of removing non-metallic inclusions by flotation were obtained for rotor I at the end of its operation.
Research on the impact of rotor wear on the effectiveness of the aluminium refining process
(2023) Socha, Ladislav; Prášil, Tomáš; Gryc, Karel; Sviželová, Jana; Saternus, Mariola; Merder, Tomasz; Pieprzyca, Jacek; Nuska, Petr
Physical modelling is successfully used to understand mechanisms involved in the aluminium refining process by injecting inert gas into the liquid metal through rotors. Two types of industrial impellers, which are extremely different in construction, were tested in the research. The aim of the research was to determine the effectiveness of their operation depending on their degree of wear. This type of research has not been tested on water models so far. During the process, the parameters were changed, such as the gas flow rate from 13 to 19 L/min, the rotor speed from 325 to 400 rpm and the height of the rotor from the bottom of the refining reactor. Tests were carried out for new and worn rotors. Oxygen removal rate curves were prepared on the basis of tests determining changes in oxygen content in the model liquid as a function of time for changing rotor speed values. It was found that the efficiency of hydrogen removal from the model liquid was higher when worn impellers were used in the model. In order to verify results of model tests, a metallographic analysis of samples obtained in industrial conditions and using the analysed process parameters was carried out.
Assessment of refining efficiency during the refining cycle in a foundry degassing unit in industrial conditions
(2024) Socha, Ladislav; Prášil, Tomáš; Gryc, Karel; Sviželová, Jana; Saternus, Mariola; Merder, Tomazs; Pieprzyca, Jacek; Nuska, Petr
The article focuses on the issue of improving the efficiency of a Foundry Degassing Unit (FDU) via operational testing of aluminium alloys during casting at MOTOR JIKOV Slévárna a.s. As part of the research, the efficiency of the refining process in the FDU was assessed. The main emphasis was placed on determining the moment of the greatest decrease in the hydrogen content in the melt and whether it is possible to shorten the refining cycle. The values of the Dichte Index were determined, on the basis of which the degassing curve was plotted and the progress of the melt degassing was assessed. To ensure the required quality of castings, the maximum allowable value of the Dichte Index ranged from 3 to 4%. During the process, the temperature drop during the refining cycle was also determined. The total temperature drop from pouring the melt into the ladle to the end of refining ranged from 26 to 32 °C, which is within the acceptable limits of the foundry. Based on the knowledge resulting from the operational experiments, recommendations were formulated to optimize the refining technology at the FDU for the MOTOR JIKOV Slévárna a.s. foundry.
Sol-gel derived silicate-phosphate glass SiO 2-P 2 O 5-CaO-TiO 2: The effect of titanium isopropoxide on porosity and thermomechanical stability
(Elsevier, 2024) Kovářík, Tomáš; Bělský, Petr; Křenek, Tomáš; Deshmukh, Kalim Abdul Rashid; Medlín, Rostislav; Beneš, Jan; Svoboda, Miloš; Kadlec, Jaroslav; Pola, Michal; Jandová, Věra; Mikysek, Petr; Ilavský, Jan; Stich, Theresia; Docheva, Denitsa; Strejcová, Kateřina; Tišler, Zdeněk; Forejtová, Jana; Forejtová, Jan
Investigation of carrier transport in ZnO and ZnO:Al thin films sputtered at different oxygen conditions
(Elsevier, 2023) Novák, Petr; Nedvědová, Lucie; Kozák, Tomáš; Šotová, Petra; Bláhová, Olga; Jansa, Zdeněk; Medlín, Rostislav; Netrvalová, Marie; Minár, Jan
Surface Pretreatments of AA5083 Aluminum Alloy with Enhanced Corrosion Protection for Cerium-Based Conversion Coatings Application: Combined Experimental and Computational Analysis
(MDPI, 2021) Mohammad Reza, Shishesaz; Moslem, Ghobadi; Najmeh, Asadi; Alireza, Zarezadeh; Ehsan, Saebnoori; Hamed, Amraei; Schubert, Jan; Chocholatý, Ondřej
Vliv předběžných povrchových úprav na konverzní povlak na bázi ceru nanesený na hliníkovou slitinu AA5083 byl zkoumán pomocí kombinace skenovací elektronové mikroskopie (SEM), energeticky disperzní rentgenové spektroskopie (EDS), polarizačního testování a elektrochemické impedanční spektroskopie. Pro studium účinků předběžných úprav povrchu byly na povrch aplikovány dva kroky předběžných úprav obsahujících kyselé nebo zásadité roztoky. Mezi předupravenými vzorky vykazoval vzorek připravený předúpravou alkalickým roztokem a následným promýváním kyselinou vyšší ochranu proti korozi (~3 řády vyšší než vzorek bez předúpravy). Tato předběžná úprava poskytla aktivnější povrch pro depozici vrstvy ceru a poskytla vhodnější substrát pro tvorbu filmu a vytvořila rovnoměrnější film. Morfologie povrchu vzorků potvrdila, že nejlepší povrchové pokrytí představovala předúprava alkalickým roztokem a následně promýváním kyselinou. Přítomnost ceru v (EDS) analýze prokázala, že předúprava alkalickým roztokem a následné promývání kyselinou vedlo k vyššímu nanášení vrstvy ceru na hliníkový povrch. Po výběru nejlepší předběžné úpravy povrchu byly zkoumány různé doby depozice cerových lázní. Nejlepšího času depozice bylo dosaženo při 10 min, po uplynutí této kritické doby se na povrchu vytvořila popraskaná vrstva, kterou nebylo možné ochránit. Korozní odolnost konverzních povlaků na bázi ceru získaná elektrochemickými testy byla použita pro trénink tří výpočetních technik (umělá neuronová síť (ANN), adaptivní neuro-fuzzy inferenční systém (ANFIS) a regrese s podpůrným vektorem (SVMR)) na základě předúpravy-1 (kyselé nebo alkalické čištění: pH (1)), předúpravy-2 (kyselé nebo alkalické čištění: pH (2)) a doby depozice v cerové lázni jako vstupu. Různá statistická kritéria ukázala, že model ANFIS (R2 = 0,99, MSE = 48,83 a MAE = 3,49) dokáže předpovědět korozní chování konverzního povlaku na bázi ceru přesněji než jiné modely. Nakonec byl vzhledem k robustnímu výkonu ANFIS při modelování zkoumán vliv jednotlivých parametrů.
Ojedinělý nález knižní spony ze Soběslavi, okr. Tábor
(Západočeské muzeum v Plzni, 2022) Čechura, Martin; Menšík, Petr; Bláhová, Olga; Vatansever, Atilla
Předmětem příspěvku je informovat o novém nálezu knižní spony nalezené pomocí detektoru kovů na okraji města Soběslav na Táborsku. Kromě archeologického a historického zhodnocení byla provedena i prvková analýza předmětu pomocí elektronové mikroskopie, která přinesla cenné poznatky složení tohoto druhu artefaktu.

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