Jozef Janovec
Slovak University of Technology, University Scientific Park, Faculty Member
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Research Interests: Materials Science, Microstructure, Metallurgy, Structural Stability, Crystal structure, and 13 moreCrack propagation, Nucleation, Chromium, Iron, Particle Size, Fracture Mechanic, Microstructures, Chemical Composition, Stress Concentration, Carbide, Temperature Effect, Brittleness, and Mechanical Property
Chemical and structural changes at the grain boundaries were investigated to quantify their influence on fracture behaviour of austenitic stainless steels and model ferritic Fe-Si-P alloys. The balance between the size and the area... more
Chemical and structural changes at the grain boundaries were investigated to quantify their influence on fracture behaviour of austenitic stainless steels and model ferritic Fe-Si-P alloys. The balance between the size and the area density of intergranular particles was found to be one of the most decisive factors influencing sensitivity of the steels to intergranular fracture. The precise dependence of the energy of intergranular fracture on the phosphorus grain boundary concentration was also determined.
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ABSTRACT The effects of intergranular precipitation (size of precipitates) and phosphorus grain boundary segregation on fracture and corrosion behaviours of the 18Cr-12Ni steel were investigated. In the investigation, techniques of light... more
ABSTRACT The effects of intergranular precipitation (size of precipitates) and phosphorus grain boundary segregation on fracture and corrosion behaviours of the 18Cr-12Ni steel were investigated. In the investigation, techniques of light microscopy, SEM, TEM, AES, EDX, electron diffraction, and the Huey test were used. A good correlation was found between the average size of intergranular particles and the portion of intergranular fracture for samples impact loaded at 173 K. The equilibrium values of phosphorus grain boundary concentration showed the close correlation with the values of weight loss (penetration depth) measured during the Huey test. French On a étudié les effets de la précipitation intergranulaire (taille des précipités) et de la ségrégation du phosphore aux joints de grain sur le comportement de fracture et de corrosion de l'acier 18Cr-12Ni. Dans cette investigation, on a utilisé des techniques variées incluant microscopie optique, SEM, TEM, AES, EDX, diffraction électronique et test de Huey. On a trouvé une bonne corrélation entre la taille moyenne des particules intergranulaires et la portion de fracture intergranulaire d'échantillons chargés par choc à 173 K. Les valeurs d'équilibres de la concentration de phosphore aux joints de grain ont montré une corrélation étroite avec les valeurs de perte de poids (profondeur de pénétration) mesurées lors du test de Huey.
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Altogether 19 alloys of an Al-Mn-Fe system with compositions near to the Taylor phase and/or the decagonal quasicrystal were characterised by the x-ray diffraction and the energy-dispersive x-ray spectroscopy coupled with the scanning... more
Altogether 19 alloys of an Al-Mn-Fe system with compositions near to the Taylor phase and/or the decagonal quasicrystal were characterised by the x-ray diffraction and the energy-dispersive x-ray spectroscopy coupled with the scanning electron microscopy, after annealing at 1000 °C for 330 h. The obtained experimental results were used to propose a partial isothermal section at 1000 °C of the Al-Mn-Fe phase diagram. The ternary T-phase area of an untypical saddle shape was found to touch the Al-Mn binary one. The γ2-phase was found to be stable between 2 and 30 at.% of Fe at 1000 °C and boundaries between γ1- and γ2-areas are expected to be located very close to the Al-Mn binary.
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Neural network (NN) models were evaluated for the prediction of suspended particulates with aerodynamic diameter less than 10-μm (PM10) concentrations. The model evaluation work considered the sequential hourly concentration time series... more
Neural network (NN) models were evaluated for the prediction of suspended particulates with aerodynamic diameter less than 10-μm (PM10) concentrations. The model evaluation work considered the sequential hourly concentration time series of PM10, which were measured at El Hamma station in Algiers. Artificial neural network models were developed using a combination of meteorological and time-scale as input variables. The results were rather satisfactory, with values of the coefficient of correlation (R2) for independent test sets ranging between 0.60 and 0.85 and values of the index of agreement (IA) between 0.87 and 0.96. In addition, the root mean square error (RMSE), the mean absolute error (MAE), the normalized mean squared error (NMSE), the absolute relative percentage error (ARPE), the fractional bias (FB), and the fractional variance (FS) were calculated to assess the performance of the model. It was seen that the overall performance of model 3 was better than models 1 and 2.
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Research Interests: Materials Science, Microstructure, Metallurgy, Steel, Niobium, and 3 moreMartensite, Austenite, and Tempering
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The characterization of phases in Al73Mn27−xFex (x=2, 4 and 6) alloys was performed using X-ray diffraction, differential thermal analysis, and scanning electron microscopy enabling energy dispersive X-ray spectroscopy. Both the annealed... more
The characterization of phases in Al73Mn27−xFex (x=2, 4 and 6) alloys was performed using X-ray diffraction, differential thermal analysis, and scanning electron microscopy enabling energy dispersive X-ray spectroscopy. Both the annealed and the thermally cycled states were studied. In the annealed states the occurrence of T-phase was expected, however it was confirmed for alloys Al73Mn25Fe2 and Al73Mn23Fe4 only. The annealing
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Research Interests: Materials Engineering, Materials Science, Crystallography, Electron Microscopy, Electron Backscatter Diffraction (EBSD), and 9 moreScanning Electron Microscopy, Intermetallics, Crystal structure, Diffraction, Energy Dispersive X-Ray Analysis, X ray diffraction, Scanning Electron Microscope, Differential Thermal Analysis, and Light microscopy
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... In terms of Watanabe's concept of grain boundary engineering [13,14], if an austenitic steel contains predominantly spe-cial, low energy boundaries, the kinetics of M23C6 precipi-tation is slower and the probability of splitting... more
... In terms of Watanabe's concept of grain boundary engineering [13,14], if an austenitic steel contains predominantly spe-cial, low energy boundaries, the kinetics of M23C6 precipi-tation is slower and the probability of splitting appearance in tensile testing is lower. ...
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Surface segregation on (100) oriented single crystal surfaces of the alloy Fe–25%Cr–2%Ni–0.14%Sb–N,S has been investigated by means of Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and X-ray photoelectron... more
Surface segregation on (100) oriented single crystal surfaces of the alloy Fe–25%Cr–2%Ni–0.14%Sb–N,S has been investigated by means of Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS). The experiments have been carried out in the temperature range from 500°C to 700°C in which a variety of segregation phenomena is observed. In the low temperature range, cosegregation of nitrogen and chromium occurs. Depth profiling and XPS studies suggest that the Cr and N segregation layer consists of (i) a two-dimensional surface compound and (ii) three-dimensional precipitates in the surface near region. A LEED investigation of the Cr and N saturated surface yields a clear (1×1) pattern after sufficiently long annealing times.At temperatures in excess of 600°C, segregated nitrogen and chromium are replaced by segregating antimony and nickel. Studies of the kinetics show that nickel and antimony jointly enrich at the sample surface; this proves that true cosegregation occurs. An XPS study of the antimony and nickel saturated surface shows that the antimony binding energy coincides with the value that had been measured for the binding energy of segregated antimony on pure iron. The corresponding LEED pattern shows reflex splitting which indicates domain formation.A further increase of the temperature to about 700°C causes segregation of sulphur displacing antimony from the surface. The sulphur covered surface exhibits a typical c(2×2) LEED pattern.
Research Interests: Materials Science, Chemistry, Crystallography, Kinetics, PHOTOELECTRON SPECTROSCOPY, and 13 moreMultidisciplinary, Single crystal surface, Nitrogen, Chromium, Iron, Nickel, Low energy electron diffraction, Single Crystal, Binding Energy, Three Dimensional, Auger electron spectroscopy, Low Temperature, and X Ray Photoelectron Spectroscopy
Research Interests: Condensed Matter Physics, Materials Science, Common Property, Anisotropy, Quantum Transport, and 13 morePhysical sciences, Electrical Resistance, Magnetic Susceptibility, Thermal Conductivity, Temperature Dependence, CHEMICAL SCIENCES, Spin Glass, Layered Structure, Hall effect, Seebeck coefficient, J, Physical Properties, and Negative Temperature Coefficient
The Sn-Ag-Cu alloys have favourable solderability and wetting properties and are, therefore, being considered as potential lead-free solder materials. In the present study, tin-based Sn-Ag-Cu and Sn-Ag-Cu-Bi alloys were studied in detail... more
The Sn-Ag-Cu alloys have favourable solderability and wetting properties and are, therefore, being considered as potential lead-free solder materials. In the present study, tin-based Sn-Ag-Cu and Sn-Ag-Cu-Bi alloys were studied in detail by a differential scanning calorimetry (DSC) and thermodynamic calculations using the CALPHAD approach. The amount of the alloying elements in the materials was chosen to be close to the respective eutectic composition and the nominal compositions were the following: Sn-3.7Ag-0.7Cu, Sn-1.0Ag-0.5Cu-1Bi (in wt.%). Thermal effects during melting and solidifying were experimentally studied by the DSC technique. The microstructure of the samples was determined by the light microscopy and the composition of solidified phases was obtained by the energy-dispersive X-ray spectroscopy, respectively. The solidification behaviour under equilibrium conditions was simulated using the Thermo-Calc software package. This approach enabled us to obtain the enthalpy of...
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The influence of increased Cu and Ag contents on the microstructure evolution in the utilized Sn-0.3Ag-0.7Cu (wt. %) solder was studied. The utilized solder was exploited in the wave soldering process at the temperatures of about 260 °C... more
The influence of increased Cu and Ag contents on the microstructure evolution in the utilized Sn-0.3Ag-0.7Cu (wt. %) solder was studied. The utilized solder was exploited in the wave soldering process at the temperatures of about 260 °C for several days. The samples investigation involved the differential scanning calorimetry, the scanning electron microscopy including the energy dispersive X-ray spectroscopy, and the X-ray diffraction techniques. To predict phase equilibria at various temperatures and temperature dependences of heat capacity, the Thermo-Calc software and the COST531 lead-free solder database were used. The original and the utilized solders were found to be very similar regarding the phase occurrence, but slightly differ from one another in microstructure evolution due to higher bulk contents of Cu in the latter solder. The obtained results contribute to both the better understanding of the microstructure evolution in low-silver Sn-Ag-Cu solders and the determinatio...
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The microstructure, phase constitution, and corrosion performance of as-solidified Al70Pd25Co5 and Al74Pd12Co14 alloys (element concentrations in at.%) have been investigated in the present work. The alloys were prepared by arc-melting of... more
The microstructure, phase constitution, and corrosion performance of as-solidified Al70Pd25Co5 and Al74Pd12Co14 alloys (element concentrations in at.%) have been investigated in the present work. The alloys were prepared by arc-melting of Al, Pd, and Co lumps in argon. The Al74Pd12Co14 alloy was composed of structurally complex εn phase, while the Al70Pd25Co5 alloy was composed of εn and δ phases. The corrosion performance was studied by open circuit potential measurements and potentiodynamic polarization in aqueous NaCl solution (3.5 wt.%). Marked open circuit potential oscillations of the Al70Pd25Co5 alloy have been observed, indicating individual breakdown and re-passivation events on the sample surface. A preferential corrosion attack of εn was found, while the binary δ phase (Al3Pd2) remained free of corrosion. A de-alloying of Al from εn and formation of intermittent interpenetrating channel networks occurred in both alloys. The corrosion behavior of εn is discussed in terms o...
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The work is aimed at searching for compositionally variant isostructural mutations of the cubic F-phase in both as-annealed (850°C/500 h) and DTA-cooled conditions of the Al72Pd9Co19 alloy. Recently, the mutations were reported for the... more
The work is aimed at searching for compositionally variant isostructural mutations of the cubic F-phase in both as-annealed (850°C/500 h) and DTA-cooled conditions of the Al72Pd9Co19 alloy. Recently, the mutations were reported for the U-phase in the Al69.8Pd13.8Co16.4 alloy annealed at 700°C for 2000 h. In the investigation, scanning electron microscopy including energy dispersive X-ray spectroscopy, powder X-ray diffraction, and differential thermal analysis (DTA) were used. Two isostructural mutations of the F-phase, FL (the product of L-parent) and FV (the product of V-parent), were identified (symbol L stands for liquid). On DTA-cooling, the bivariant heterogeneous transition (Lpart→V), the monovariant heterogeneous transformation (Lrest→V+FL), and the monovariant quasi-eutectoid transformation (Vrest→Al5Co2+FV) were recorded.
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Three austenitic steels (18Cr–8Ni, 18Cr–10Ni, 21Cr–30Ni), used for long-term applications at temperatures between 600 and 800 °C were investigated. In the investigation, metallography, transmission electron microscopy, selected area... more
Three austenitic steels (18Cr–8Ni, 18Cr–10Ni, 21Cr–30Ni), used for long-term applications at temperatures between 600 and 800 °C were investigated. In the investigation, metallography, transmission electron microscopy, selected area electron diffraction, energy dispersive X-ray spectroscopy, and scanning electron microscopy were used. In additional to the experimental measurements, thermodynamic predictions were done using the ThermoCalc software and the non-commercial database STEEL16F. Various combinations of M23C6, sigma, and MC phases were identified in the austenite matrix of these steels. It was confirmed experimentally that extra large particles (up to 10 μm) observed in the 21Cr–30Ni steel are M23C6, even though this carbide was not predicted as the equilibrium carbide at service temperature (800 °C). The analytical-experimental approach, combining thermodynamic predictions and experimental measurements, was found to be reliable for the characterization of austenitic steels.
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Al68Pd14.6Co17.4, Al69.8Pd13.8Co16.4, Al72Pd12.8Co15.2, Al73.8Pd11.9Co14.3, and Al76Pd11Co13 alloys annealed at 700 ∘C for 2000 h were studied. In the investigation, scanning electron microscopy including energy dispersive X-ray... more
Al68Pd14.6Co17.4, Al69.8Pd13.8Co16.4, Al72Pd12.8Co15.2, Al73.8Pd11.9Co14.3, and Al76Pd11Co13 alloys annealed at 700 ∘C for 2000 h were studied. In the investigation, scanning electron microscopy including energy dispersive X-ray spectroscopy and electron backscatter diffraction, X-ray diffraction, and transmission electron microscopy were used. Altogether five near-equilibrium phases (β, U, Al5Co2, e, Al9Co2) were identified. Transitions between β, U, and e phases were also determined dependent on the alloy bulk metal composition. The experimental results were used to propose the partial isothermal section of the Al–Pd–Co phase diagram at 700 ∘C. The maximum solubilities at 700 ∘C of Pd in Al9Co2 and Al5Co2 were determined as 1.7 and 2.69 at.%, respectively.
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Abstract Three austenitic steels (18Cr-8Ni, 18Cr-10Ni, and 21Cr-30Ni) exploited for long periods of time at temperatures between 600°C and 800°C were investigated. In the investigation, electrochemical potentiokinetic reactivation-double... more
Abstract Three austenitic steels (18Cr-8Ni, 18Cr-10Ni, and 21Cr-30Ni) exploited for long periods of time at temperatures between 600°C and 800°C were investigated. In the investigation, electrochemical potentiokinetic reactivation-double loop (EPR-DL) and oxalic acid etch corrosion tests, metallography, scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and energy-dispersive x-ray spectroscopy were used. In the severe sensitized 18Cr-8Ni steel, small, densely arranged intergranular particles, mostly of M23C6, were found. The 18Cr-10Ni steel was classified as less-sensitized compared to the 18Cr-8Ni steel as a result of the presence of larger, discrete grain boundary particles in addition to small, densely arranged particles. In the unsensitized 21Cr-30Ni steel, huge, discrete clusters often exceeding 10 μm were observed at the grain boundaries. The clusters were found to consist of large Cr-rich M23C6 and small Ti-rich MC particles.
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ABSTRACT A 12% Cr-steel was investigated by TEM after aging at 773 K for up to 22,000 h. In addition to the carbides M{sub 23}C{sub 6} and MC an intermetallic phase was observed after aging for 22,000 h. This phase contained mainly Mo, Fe... more
ABSTRACT A 12% Cr-steel was investigated by TEM after aging at 773 K for up to 22,000 h. In addition to the carbides M{sub 23}C{sub 6} and MC an intermetallic phase was observed after aging for 22,000 h. This phase contained mainly Mo, Fe and Cr and additionally Si and P. These particles occurred in three different morphologies (mosaic, lamellar and compact) and were mainly found to be located close to the carbides. The chemical composition was similar to that of the Laves-Phase (Fe,Cr){sub 2}Mo, but the precipitates showed five-, six- and two-fold symmetries and were therefore classified as quasicrystals having icosahedral symmetry.
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ABSTRACT Four low alloy steels with different contents of molybdenum and vanadium were investigated. The steels were annealed at 773, 793, 853, 873, 933, 973, and 993K for 500, 1000, 3000, and 10000h. Techniques of transmission electron... more
ABSTRACT Four low alloy steels with different contents of molybdenum and vanadium were investigated. The steels were annealed at 773, 793, 853, 873, 933, 973, and 993K for 500, 1000, 3000, and 10000h. Techniques of transmission electron microscopy and thermodynamic calculations (ThermoCalc) were used to characterise influence of the steel bulk composition and the annealing conditions on evolution of carbides M3C, M2C, M7C3, M23C6, M6C, and MC (M=metallic element). Changes in structure types and metal compositions of the carbides were characterised in detail. The work was done with the intention to obtain more information about the secondary phase evolution in low alloy steels used in energy industries.
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ABSTRACT Metallographic observations and thermodynamic calculations were used to characterise the solidification and the microstructure formation during casting in three modifications of CF3M steel. By combining the results it was... more
ABSTRACT Metallographic observations and thermodynamic calculations were used to characterise the solidification and the microstructure formation during casting in three modifications of CF3M steel. By combining the results it was possible to outline the basic microstructure changes which are the same for all three modifications. It was shown that light microscopy is more useful for material characterisation when it is combined with credible thermodynamic predictions, and vice versa.