DOAJ (DOAJ: Directory of Open Access Journals), Jul 1, 2013
In the frame of this work, Al-5Ni-1Co-3RE (RE-Rare Earth (Mischmetal)) rapidly solidifi ed ribbon... more In the frame of this work, Al-5Ni-1Co-3RE (RE-Rare Earth (Mischmetal)) rapidly solidifi ed ribbons were manufactured and analyzed. The morphology of the as-cast structure, as well as the microstructural features were analyzed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Thermal stability has been investigated by combination of four point scanning electrical resistivity measurement (ER), diff erential scanning calorimetry (DSC) and microhardness measurement. From the results we can conclude, that Al-5Ni-1Co-3RE rapidly solidifi ed alloys have good thermal stability due to very slow coarsening kinetics of precipitated particles.
Journal of achievements in materials and manufacturing engineering, 2011
Purpose: In the case of continuous casting of metal ribbons with the melt-spinning process on the... more Purpose: In the case of continuous casting of metal ribbons with the melt-spinning process on the industrial scale, larger quantity of melt could lead to a slow excessive warming of the chilling wheel, which would further lead to solidification of a ribbon at non-uniform conditions and increased wearing of the wheel. Primary goal of our work was to determine to what extent the release of heat during contact of the melt/ribbon on the circumferential surface of the chilling wheel affect its surface temperature rise, and inversely how much elevated temperature of the chill wheel surface affects on metal ribbon cooling rate and its solidification velocity. Design/methodology/approach: On the basis of developed mathematical model, a computer program was made and used for analyses of heat transfer in the melt-spinning process. Findings: The calculations show that contact resistance between metal melt and chilling wheel has a great influence on melt/ribbon cooling and chill wheel heating rate, and must not be neglected in numerical calculations, even if its value is very low. In the case of continuous casting, significant "long term" surface temperature increase may take place, if the wheel is not internally cooled. But inner cooling is effective only if wheel casing thickness is properly chosen. Research limitations/implications: Influence of process parameters and chill wheel cooling mode on cooling and solidifying rate over ribbon thickness are outlined. Practical implications: Directions for the chill wheel cooling system design are indicated. Originality/value: New method for determining contact resistance through variable heat transfer coefficient is introduced which takes into account physical properties of the casting material, process parameters and contact time/length between metal melt/ribbon and substrate and enables cooling rate prediction before the experiment execution. In the case of continuous casting, heat balance of the melt-spinning process is calculated and influence of the chill wheel cooling mode on cooling rate of metallic ribbon is analyzed.
Chromium-molybdenum steel (16Mo3) is widely used in petroleum, gas, automotive, and construction ... more Chromium-molybdenum steel (16Mo3) is widely used in petroleum, gas, automotive, and construction industries due to its good oxidation resistance and mechanical properties at moderately elevated temperatures. The aim of the research was to evaluate the corrosion susceptibility of 16Mo3 steel in hot rolled and aluminized states. Aluminization was performed by diffusion pack aluminization process at 900 °C / 2h and 730 °C / 4h, respectively. Electrochemical corrosion testing included measuring open circuit potential (EOCP), linear polarization resistance (LPR), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) in potassium phosphate buffer (KH 2 PO 4 , pH = 7). Optical microscopy (OM), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS) were used for surface layer microstructure characterization before and after corrosion tests. It was demonstrated that corrosion resistance of aluminized steel increased substantially. Corrosion properties were related to the structure and properties of intermetallic phase (FeAl, FeAl 2 and Fe 2 Al 5) that formed on the surface of 16Mo3 steel.
Scandium (Sc) is known to be one of the most effective alloying elements of aluminum alloys. The ... more Scandium (Sc) is known to be one of the most effective alloying elements of aluminum alloys. The only drawback is its high price, but that could change quickly due to the promising results of recent research on its extraction. However, the data on how it affects anodic oxidation are very scarce. In this research, we analyzed how a micro-addition of Sc to the AlMg alloy affects the growth mechanism and properties of the protective aluminium oxide layer depending on the anodization parameters. For comparison, alloy AA5083 with a similar magnesium content was also anodized with the same anodizing parameters. In all experiments, sulfuric acid (VI) with concentrations of 1.72 M or 2.2 M at temperatures of 21 °C or 35 °C was used as the electrolyte. Potentiostatic (18 V) and galvanostatic (20 mA/cm2) anodizing methods were applied. The results (SED-EDS) show that scandium is uniformly intercalated in the matrix of the oxide layer and decreases its resistivity, which increases the oxide gr...
Steels from the group PROTAC are distinguished by good mechanical properties and excellent armour... more Steels from the group PROTAC are distinguished by good mechanical properties and excellent armour properties even at small thicknesses. The mechanical properties of PROTAC 600 steel are known, while data on thermal properties (thermal conductivity, specific heat and temperature conductivity) are not available, so in the frame of our work we determined its thermal properties. As the first part of the work, a study and evaluation of the operation of the device for determining the thermal properties of Hot Disk TPS 2200, today one of the more modern and high-quality instruments for determining thermal properties. In the second part of the work, we performed measurements of thermal properties in accordance with the standard ISO 22007-2 at ambient temperature. The values of thermal properties of PROTAC 600 steel at ambient temperature (approximately 22 °C) are: thermal conductivity 28.69 W/mK, specific heat 3.94 MJ/m3K, and temperature conductivity 7.29 mm2/s. We found that steel PROTAC 600 has more than 10% higher heat conductivity in comparison with the steel of previous generation PROTAC 500.
In the present work, free-cutting aluminum alloy AA6026 with 1.1 wt.% bismuth addition was fabric... more In the present work, free-cutting aluminum alloy AA6026 with 1.1 wt.% bismuth addition was fabricated by different melt preparation methods in order to investigate whether the melt preparation route affects the solidification sequence and thus has an influence on the machinability of the alloy. All experiments were designed to simulate variable industrial conditions: addition of bismuth in an induction melting furnace, addition of bismuth in an electric resistance holding furnace, addition of bismuth together with grain refiner, effect of holding time and melt temperature before casting. Detailed thermodynamic analyses (DSC, Thermo-Calc) and microstructural characterization (SEM-EDS, XRD) have been performed to explain the solidification sequence, microstructure development and especially formation of the intermetallic Mg3Bi2 phase.
The main task of the research was to find out why sometimes cracking of the enamelled layer occur... more The main task of the research was to find out why sometimes cracking of the enamelled layer occur and to what extent enamel layer affects the heat tra
In this paper, industrial control measurements of the heat treatment of high chromium steel (HCS)... more In this paper, industrial control measurements of the heat treatment of high chromium steel (HCS) rolls is presented. Measurements of the gas fired car bottom chamber furnace Bosio PP- KP 70/1150 were carried out in the company Valji d. o. o., Store, Slovenia. Temperature in the individual heating zones of the furnace, temperatures of the roll surface, furnace external walls, and gas consumption was monitored throughout the whole process of heat treatment. The temperature profile of the rolls cross-section was calculated using computer simulation. Periodical measurements of CO and NOx emissions were also carried out with the aim of combustion evaluation and ecological integrity. The successfulness of heat treatment was examined through microstructure observation, hardness measurement, and the amount of retained austenite in the heat treated rolls.
Journal of achievements in materials and manufacturing engineering, 2012
Purpose: Rapid solidification (RS) of metallic melts is important for the development of the adva... more Purpose: Rapid solidification (RS) of metallic melts is important for the development of the advance metallic materials, because enables the production of new alloys with superior properties according to conventionally treated alloys. In practice it turned out, that single roll melt spinning process has one of the highest melt cooling rates among all continuous casting processes. But, because very short solidification time and movement of the melt and substrate, melt cooling rate is very difficult to measure with confidence. Primary goal of our work was to determine the limits of cooling rate over the ribbon thickness and to outline, which property or typical feature of the process has the greatest influence on cooling rate of the melt. Design/methodology/approach: On the basis of developed mathematical model, a computer program was made and used for melt cooling rate calculation in the melt-spinning process. Findings: The calculations show that distance from the contact surface in ...
In this paper, industrial control technical measurements of the heat treatment of high chromium s... more In this paper, industrial control technical measurements of the heat treatment of high chromium steel rolls (HCS), is presented. Measurements were carried out on the gas fired car bottom chamber furnace Bosio PP-KP 70/1150 in the company Valji d. o. o., Store, Slovenia. Temperature measurements of the individual heating zones of the furnace, rolls surfaces, the external walls of the furnace and gas consumption were monitored throughout the whole process of heat treatment. The temperature profile of the rolls cross-section was calculated using computer simulation. Periodical measurements of CO and NOx emissions were also carried out with the aim of combustion evaluation and ecological integrity. The successfulness of heat treatment was examined through microstructure observation, hardness measurement and the amount of retained austenite in the heat treated rolls.
A. Nagode, M. Bizjak, B. Kosec, B. Karpe, B. Zorc, Faculty of Natural Sciences and Engineering, U... more A. Nagode, M. Bizjak, B. Kosec, B. Karpe, B. Zorc, Faculty of Natural Sciences and Engineering, University of Ljubljana, Ljubljana, Slovenia; A. Resnik, Štore Steel d.o.o., Štore, Slovenia; G. Kosec, Acroni do.o.o, Jesenice, Slovenija, I. Budak, Faculty of technical Sicences, University of Novi Sad, Novi Sad, Serbia In this paper the development of a banded microstructure in hot-rolled 34CrNiMo6 steel which consisted of bainitic and martensitic bands is explained. The chemical compositions of the bands were measured with energy dispersive x-ray spectroscopy (EDS), which showed that the martensitic bands contained more alloying elements (Mn, Cr, Mo, Si) than bainitic bands. By using Oberhoffer reagent, the segregations of phosphorus were also revealed. These phosphorus segregations coincided with the positive segregations of the alloying elements. The continuous cooling transformation (CCT) diagrams of steel were calculated. They confirmed the formation of martensite in positive segr...
Precipitation sequence and microstructure decomposition during heating of rapidly solidified Cu-F... more Precipitation sequence and microstructure decomposition during heating of rapidly solidified Cu-Fe and Cu-Fe-Ti alloys have been investigated by the combination of four point electrical resistance measurement method, optical microscopy and scanning electron microscopy (SEM). Rapidly solidified samples, in the form of thin ribbons, were prepared by the single roll melt spun technique and heated in the protective atmosphere with constant heating rate to 800 °C. Sequence of the phase precipitation during heating were successfully followed by the in-situ electrical resistance measurement method. After recording the electrical resistivity temperature dependency in the entire temperature interval, separate samples were heated to various temperatures, slowly cooled and analyzed by scanning (SEM) electron microscopy. It was found that titanium reacts with iron and forms intermetalic phase TiFe. The microstructure transformation starts at a higher temperature than for binary Cu-Fe alloys and...
Pack aluminization process is one of the possible production methods to improve oxidation resista... more Pack aluminization process is one of the possible production methods to improve oxidation resistance at high temperatures of various types of metallic materials. It is a chemo-thermal process where products are embedded in the powder mixture, consisting of Al powder, halide activator NH4Cl, and inert diluent Al2O3 powder, and annealed at high temperature. This exposure to high temperature causes the Al diffusion into the base material and formation of the aluminide surface layer. During the component service at elevated temperatures, the oxidation resistance is obtained due to the constant formation of an aluminium oxide film that forms on the aluminide surface layer and acts as an oxygen impermeable barrier. In the present study, FeCrAl and the NiCr heat resistant alloys in the form of 1mm thick sheet were aluminized at various process parameters. The effect of time, temperature, concentration of aluminium and halide activator in the powder mixture as well as the influence of furna...
The purpose of this work was a characterisation of the microstructure, certain mechanical propert... more The purpose of this work was a characterisation of the microstructure, certain mechanical properties (compressive strength, hardness) and thermal characteristics of a restorative dental composite. Three composite testing samples were made in the shape of a cylinder. Regarding the composite polymerisation, two routes were performed: 1) applying multiple layers from which the final sample was composed and curing each of the layers separately, and 2) applying the whole volume of the composite sample and then curing the surface across the whole sample. The surfaces of both samples and the microstructure analysis of the composite material were performed with a scanning electron microscope (SEM) and an attached EDXS detector. Then the compressive strength, hardness and thermal conductivity were also measured. Based on the performed tests, it was found that the analysed dental restorative composite had applicable studied properties, and the composite meets the clinical requirements for use as a dental restorative material.
Sol-gel boehmite coatings were produced on the polished surfaces of hypo-eutectoid C45carbon stee... more Sol-gel boehmite coatings were produced on the polished surfaces of hypo-eutectoid C45carbon steel by dip coating. After the deposition the coatings were heat treated by drying at RT, 150 and 200°C. It was found that for crack-free coatings, the drying temperature needs to be ≥150°C. Properly heat-treated boehmite coatings then improve the corrosion resistance of steel, while proposed alumina coatings derived from the boehmite coatings during annealing of the steel affect the decarburization. The coated steel samples were annealed at temperatures that are typical for the heat-treatment and thermomechanical process of C45 steel, i.e., <A C1 (tempering, sphereoidization) and >A C3 (austenitization, thermomechanical process). The sol-gel alumina coating decreased the decarburization rate of the quenched steel during the tempering (≤600°C), which meant that the hardness reduction on the steel surface was smaller. Alumina coatings have a smaller effect on the decarburization at higher temperatures; however, the metallographic analyses indicate that the coatings can retard the oxidation rate in comparison to the decarburization rate and thus, somewhat increase the visual level of the decarburization. Under annealing conditions (T = 950°C, t = 0.5-2 h) at which the oxidation rate is higher than the decarburization rate the decarburization process is not important since the decarburized layer is peeled off the steel surface together with the scale. No visual decarburization is then observed.
Journal of Mining and Metallurgy, Section B: Metallurgy, 2019
In the present study, the corrosion mechanism of commercial FeCrAl alloy (Kanthal AF) during anne... more In the present study, the corrosion mechanism of commercial FeCrAl alloy (Kanthal AF) during annealing in nitrogen gas (4.6) at 900?C and 1200?C is outlined. Isothermal and thermo-cyclic tests with varying total exposure times, heating rates, and annealing temperatures were performed. Oxidation test in air and nitrogen gas were carried out by thermogravimetric analysis. The microstructure is characterized by scanning electron microscopy (SEM-EDX), Auger electron spectroscopy (AES), and focused ion beam (FIB-EDX) analysis. The results show that the progression of corrosion takes place through the formation of localized subsurface nitridation regions, composed of AlN phase particles, which reduces the aluminum activity and causes embrittlement and spallation. The processes of Al-nitride formation and Al-oxide scale growth depend on annealing temperature and heating rate. It was found that nitridation of the FeCrAl alloy is a faster process than oxidation during annealing in a nitrogen...
Today almost all manufacturers of dental materials in their certificates of material quality desc... more Today almost all manufacturers of dental materials in their certificates of material quality describe material chemical composition, mechanical properties, process ability and aesthetic characteristics, while information about thermal properties are not available. Within the interdisciplinary and international teamwork, thermal properties of five selected dental materials were measured, by modern transient plane source method in accordance with standard ISO 22007-2. Thermal properties were measured at temperature interval between 7 °C and 45 °C.
DOAJ (DOAJ: Directory of Open Access Journals), Jul 1, 2013
In the frame of this work, Al-5Ni-1Co-3RE (RE-Rare Earth (Mischmetal)) rapidly solidifi ed ribbon... more In the frame of this work, Al-5Ni-1Co-3RE (RE-Rare Earth (Mischmetal)) rapidly solidifi ed ribbons were manufactured and analyzed. The morphology of the as-cast structure, as well as the microstructural features were analyzed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Thermal stability has been investigated by combination of four point scanning electrical resistivity measurement (ER), diff erential scanning calorimetry (DSC) and microhardness measurement. From the results we can conclude, that Al-5Ni-1Co-3RE rapidly solidifi ed alloys have good thermal stability due to very slow coarsening kinetics of precipitated particles.
Journal of achievements in materials and manufacturing engineering, 2011
Purpose: In the case of continuous casting of metal ribbons with the melt-spinning process on the... more Purpose: In the case of continuous casting of metal ribbons with the melt-spinning process on the industrial scale, larger quantity of melt could lead to a slow excessive warming of the chilling wheel, which would further lead to solidification of a ribbon at non-uniform conditions and increased wearing of the wheel. Primary goal of our work was to determine to what extent the release of heat during contact of the melt/ribbon on the circumferential surface of the chilling wheel affect its surface temperature rise, and inversely how much elevated temperature of the chill wheel surface affects on metal ribbon cooling rate and its solidification velocity. Design/methodology/approach: On the basis of developed mathematical model, a computer program was made and used for analyses of heat transfer in the melt-spinning process. Findings: The calculations show that contact resistance between metal melt and chilling wheel has a great influence on melt/ribbon cooling and chill wheel heating rate, and must not be neglected in numerical calculations, even if its value is very low. In the case of continuous casting, significant "long term" surface temperature increase may take place, if the wheel is not internally cooled. But inner cooling is effective only if wheel casing thickness is properly chosen. Research limitations/implications: Influence of process parameters and chill wheel cooling mode on cooling and solidifying rate over ribbon thickness are outlined. Practical implications: Directions for the chill wheel cooling system design are indicated. Originality/value: New method for determining contact resistance through variable heat transfer coefficient is introduced which takes into account physical properties of the casting material, process parameters and contact time/length between metal melt/ribbon and substrate and enables cooling rate prediction before the experiment execution. In the case of continuous casting, heat balance of the melt-spinning process is calculated and influence of the chill wheel cooling mode on cooling rate of metallic ribbon is analyzed.
Chromium-molybdenum steel (16Mo3) is widely used in petroleum, gas, automotive, and construction ... more Chromium-molybdenum steel (16Mo3) is widely used in petroleum, gas, automotive, and construction industries due to its good oxidation resistance and mechanical properties at moderately elevated temperatures. The aim of the research was to evaluate the corrosion susceptibility of 16Mo3 steel in hot rolled and aluminized states. Aluminization was performed by diffusion pack aluminization process at 900 °C / 2h and 730 °C / 4h, respectively. Electrochemical corrosion testing included measuring open circuit potential (EOCP), linear polarization resistance (LPR), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) in potassium phosphate buffer (KH 2 PO 4 , pH = 7). Optical microscopy (OM), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS) were used for surface layer microstructure characterization before and after corrosion tests. It was demonstrated that corrosion resistance of aluminized steel increased substantially. Corrosion properties were related to the structure and properties of intermetallic phase (FeAl, FeAl 2 and Fe 2 Al 5) that formed on the surface of 16Mo3 steel.
Scandium (Sc) is known to be one of the most effective alloying elements of aluminum alloys. The ... more Scandium (Sc) is known to be one of the most effective alloying elements of aluminum alloys. The only drawback is its high price, but that could change quickly due to the promising results of recent research on its extraction. However, the data on how it affects anodic oxidation are very scarce. In this research, we analyzed how a micro-addition of Sc to the AlMg alloy affects the growth mechanism and properties of the protective aluminium oxide layer depending on the anodization parameters. For comparison, alloy AA5083 with a similar magnesium content was also anodized with the same anodizing parameters. In all experiments, sulfuric acid (VI) with concentrations of 1.72 M or 2.2 M at temperatures of 21 °C or 35 °C was used as the electrolyte. Potentiostatic (18 V) and galvanostatic (20 mA/cm2) anodizing methods were applied. The results (SED-EDS) show that scandium is uniformly intercalated in the matrix of the oxide layer and decreases its resistivity, which increases the oxide gr...
Steels from the group PROTAC are distinguished by good mechanical properties and excellent armour... more Steels from the group PROTAC are distinguished by good mechanical properties and excellent armour properties even at small thicknesses. The mechanical properties of PROTAC 600 steel are known, while data on thermal properties (thermal conductivity, specific heat and temperature conductivity) are not available, so in the frame of our work we determined its thermal properties. As the first part of the work, a study and evaluation of the operation of the device for determining the thermal properties of Hot Disk TPS 2200, today one of the more modern and high-quality instruments for determining thermal properties. In the second part of the work, we performed measurements of thermal properties in accordance with the standard ISO 22007-2 at ambient temperature. The values of thermal properties of PROTAC 600 steel at ambient temperature (approximately 22 °C) are: thermal conductivity 28.69 W/mK, specific heat 3.94 MJ/m3K, and temperature conductivity 7.29 mm2/s. We found that steel PROTAC 600 has more than 10% higher heat conductivity in comparison with the steel of previous generation PROTAC 500.
In the present work, free-cutting aluminum alloy AA6026 with 1.1 wt.% bismuth addition was fabric... more In the present work, free-cutting aluminum alloy AA6026 with 1.1 wt.% bismuth addition was fabricated by different melt preparation methods in order to investigate whether the melt preparation route affects the solidification sequence and thus has an influence on the machinability of the alloy. All experiments were designed to simulate variable industrial conditions: addition of bismuth in an induction melting furnace, addition of bismuth in an electric resistance holding furnace, addition of bismuth together with grain refiner, effect of holding time and melt temperature before casting. Detailed thermodynamic analyses (DSC, Thermo-Calc) and microstructural characterization (SEM-EDS, XRD) have been performed to explain the solidification sequence, microstructure development and especially formation of the intermetallic Mg3Bi2 phase.
The main task of the research was to find out why sometimes cracking of the enamelled layer occur... more The main task of the research was to find out why sometimes cracking of the enamelled layer occur and to what extent enamel layer affects the heat tra
In this paper, industrial control measurements of the heat treatment of high chromium steel (HCS)... more In this paper, industrial control measurements of the heat treatment of high chromium steel (HCS) rolls is presented. Measurements of the gas fired car bottom chamber furnace Bosio PP- KP 70/1150 were carried out in the company Valji d. o. o., Store, Slovenia. Temperature in the individual heating zones of the furnace, temperatures of the roll surface, furnace external walls, and gas consumption was monitored throughout the whole process of heat treatment. The temperature profile of the rolls cross-section was calculated using computer simulation. Periodical measurements of CO and NOx emissions were also carried out with the aim of combustion evaluation and ecological integrity. The successfulness of heat treatment was examined through microstructure observation, hardness measurement, and the amount of retained austenite in the heat treated rolls.
Journal of achievements in materials and manufacturing engineering, 2012
Purpose: Rapid solidification (RS) of metallic melts is important for the development of the adva... more Purpose: Rapid solidification (RS) of metallic melts is important for the development of the advance metallic materials, because enables the production of new alloys with superior properties according to conventionally treated alloys. In practice it turned out, that single roll melt spinning process has one of the highest melt cooling rates among all continuous casting processes. But, because very short solidification time and movement of the melt and substrate, melt cooling rate is very difficult to measure with confidence. Primary goal of our work was to determine the limits of cooling rate over the ribbon thickness and to outline, which property or typical feature of the process has the greatest influence on cooling rate of the melt. Design/methodology/approach: On the basis of developed mathematical model, a computer program was made and used for melt cooling rate calculation in the melt-spinning process. Findings: The calculations show that distance from the contact surface in ...
In this paper, industrial control technical measurements of the heat treatment of high chromium s... more In this paper, industrial control technical measurements of the heat treatment of high chromium steel rolls (HCS), is presented. Measurements were carried out on the gas fired car bottom chamber furnace Bosio PP-KP 70/1150 in the company Valji d. o. o., Store, Slovenia. Temperature measurements of the individual heating zones of the furnace, rolls surfaces, the external walls of the furnace and gas consumption were monitored throughout the whole process of heat treatment. The temperature profile of the rolls cross-section was calculated using computer simulation. Periodical measurements of CO and NOx emissions were also carried out with the aim of combustion evaluation and ecological integrity. The successfulness of heat treatment was examined through microstructure observation, hardness measurement and the amount of retained austenite in the heat treated rolls.
A. Nagode, M. Bizjak, B. Kosec, B. Karpe, B. Zorc, Faculty of Natural Sciences and Engineering, U... more A. Nagode, M. Bizjak, B. Kosec, B. Karpe, B. Zorc, Faculty of Natural Sciences and Engineering, University of Ljubljana, Ljubljana, Slovenia; A. Resnik, Štore Steel d.o.o., Štore, Slovenia; G. Kosec, Acroni do.o.o, Jesenice, Slovenija, I. Budak, Faculty of technical Sicences, University of Novi Sad, Novi Sad, Serbia In this paper the development of a banded microstructure in hot-rolled 34CrNiMo6 steel which consisted of bainitic and martensitic bands is explained. The chemical compositions of the bands were measured with energy dispersive x-ray spectroscopy (EDS), which showed that the martensitic bands contained more alloying elements (Mn, Cr, Mo, Si) than bainitic bands. By using Oberhoffer reagent, the segregations of phosphorus were also revealed. These phosphorus segregations coincided with the positive segregations of the alloying elements. The continuous cooling transformation (CCT) diagrams of steel were calculated. They confirmed the formation of martensite in positive segr...
Precipitation sequence and microstructure decomposition during heating of rapidly solidified Cu-F... more Precipitation sequence and microstructure decomposition during heating of rapidly solidified Cu-Fe and Cu-Fe-Ti alloys have been investigated by the combination of four point electrical resistance measurement method, optical microscopy and scanning electron microscopy (SEM). Rapidly solidified samples, in the form of thin ribbons, were prepared by the single roll melt spun technique and heated in the protective atmosphere with constant heating rate to 800 °C. Sequence of the phase precipitation during heating were successfully followed by the in-situ electrical resistance measurement method. After recording the electrical resistivity temperature dependency in the entire temperature interval, separate samples were heated to various temperatures, slowly cooled and analyzed by scanning (SEM) electron microscopy. It was found that titanium reacts with iron and forms intermetalic phase TiFe. The microstructure transformation starts at a higher temperature than for binary Cu-Fe alloys and...
Pack aluminization process is one of the possible production methods to improve oxidation resista... more Pack aluminization process is one of the possible production methods to improve oxidation resistance at high temperatures of various types of metallic materials. It is a chemo-thermal process where products are embedded in the powder mixture, consisting of Al powder, halide activator NH4Cl, and inert diluent Al2O3 powder, and annealed at high temperature. This exposure to high temperature causes the Al diffusion into the base material and formation of the aluminide surface layer. During the component service at elevated temperatures, the oxidation resistance is obtained due to the constant formation of an aluminium oxide film that forms on the aluminide surface layer and acts as an oxygen impermeable barrier. In the present study, FeCrAl and the NiCr heat resistant alloys in the form of 1mm thick sheet were aluminized at various process parameters. The effect of time, temperature, concentration of aluminium and halide activator in the powder mixture as well as the influence of furna...
The purpose of this work was a characterisation of the microstructure, certain mechanical propert... more The purpose of this work was a characterisation of the microstructure, certain mechanical properties (compressive strength, hardness) and thermal characteristics of a restorative dental composite. Three composite testing samples were made in the shape of a cylinder. Regarding the composite polymerisation, two routes were performed: 1) applying multiple layers from which the final sample was composed and curing each of the layers separately, and 2) applying the whole volume of the composite sample and then curing the surface across the whole sample. The surfaces of both samples and the microstructure analysis of the composite material were performed with a scanning electron microscope (SEM) and an attached EDXS detector. Then the compressive strength, hardness and thermal conductivity were also measured. Based on the performed tests, it was found that the analysed dental restorative composite had applicable studied properties, and the composite meets the clinical requirements for use as a dental restorative material.
Sol-gel boehmite coatings were produced on the polished surfaces of hypo-eutectoid C45carbon stee... more Sol-gel boehmite coatings were produced on the polished surfaces of hypo-eutectoid C45carbon steel by dip coating. After the deposition the coatings were heat treated by drying at RT, 150 and 200°C. It was found that for crack-free coatings, the drying temperature needs to be ≥150°C. Properly heat-treated boehmite coatings then improve the corrosion resistance of steel, while proposed alumina coatings derived from the boehmite coatings during annealing of the steel affect the decarburization. The coated steel samples were annealed at temperatures that are typical for the heat-treatment and thermomechanical process of C45 steel, i.e., <A C1 (tempering, sphereoidization) and >A C3 (austenitization, thermomechanical process). The sol-gel alumina coating decreased the decarburization rate of the quenched steel during the tempering (≤600°C), which meant that the hardness reduction on the steel surface was smaller. Alumina coatings have a smaller effect on the decarburization at higher temperatures; however, the metallographic analyses indicate that the coatings can retard the oxidation rate in comparison to the decarburization rate and thus, somewhat increase the visual level of the decarburization. Under annealing conditions (T = 950°C, t = 0.5-2 h) at which the oxidation rate is higher than the decarburization rate the decarburization process is not important since the decarburized layer is peeled off the steel surface together with the scale. No visual decarburization is then observed.
Journal of Mining and Metallurgy, Section B: Metallurgy, 2019
In the present study, the corrosion mechanism of commercial FeCrAl alloy (Kanthal AF) during anne... more In the present study, the corrosion mechanism of commercial FeCrAl alloy (Kanthal AF) during annealing in nitrogen gas (4.6) at 900?C and 1200?C is outlined. Isothermal and thermo-cyclic tests with varying total exposure times, heating rates, and annealing temperatures were performed. Oxidation test in air and nitrogen gas were carried out by thermogravimetric analysis. The microstructure is characterized by scanning electron microscopy (SEM-EDX), Auger electron spectroscopy (AES), and focused ion beam (FIB-EDX) analysis. The results show that the progression of corrosion takes place through the formation of localized subsurface nitridation regions, composed of AlN phase particles, which reduces the aluminum activity and causes embrittlement and spallation. The processes of Al-nitride formation and Al-oxide scale growth depend on annealing temperature and heating rate. It was found that nitridation of the FeCrAl alloy is a faster process than oxidation during annealing in a nitrogen...
Today almost all manufacturers of dental materials in their certificates of material quality desc... more Today almost all manufacturers of dental materials in their certificates of material quality describe material chemical composition, mechanical properties, process ability and aesthetic characteristics, while information about thermal properties are not available. Within the interdisciplinary and international teamwork, thermal properties of five selected dental materials were measured, by modern transient plane source method in accordance with standard ISO 22007-2. Thermal properties were measured at temperature interval between 7 °C and 45 °C.
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