Tamás Mikó - Academia.edu (original) (raw)

Papers by Tamás Mikó

International Journal of Refractory Metals and Hard Materials, 2021

W and Cu can be found in separate phases in the W-Cu composites since these elements do not disso... more W and Cu can be found in separate phases in the W-Cu composites since these elements do not dissolve in each other neither in liquid nor in solid phase, but with mechanical alloying it is possible to produce nonequilibrium W-Cu alloys In this work the nanostructured W-Cu composites were produced by planetary ball milling. The nanostructured W-Cu powder was sintered on 900°C and 950°C with 50 MPa pressure applied. The meso-and microstructure of the W-Cu powder and the sintered samples, were investigated with SEM, TEM and XRD. After 50 hours of milling, the size of the W crystallites was ~ 10 nm, and about 10 % of the Cu was solved in the W matrix, producing a W-Cu nonequilibrium alloy layer on the surface of W nano crystallites. During sintering, the Cu atoms left from the W surface to the Cu phases, so the W-Cu nonequilibrium alloy layer disappeared. The size of the W crystallitesafter 60 min of sintering on 950°C-was around 170 nm, and the relative density was ~90% of the theoretical density.

IOP Conference Series: Materials Science and Engineering, Oct 18, 2018

Properties of powders made from Ti50Cu27,5Ni10Zr10Co2,5 alloy, milled under different conditions ... more Properties of powders made from Ti50Cu27,5Ni10Zr10Co2,5 alloy, milled under different conditions for only 3600 s in total were investigated. For this purpose two different milling atmospheres and two different Process Control Agents (PCA) were tested: argon without PCA, air without PCA, argon combined with stearic acid, argon combined with petroleum spirit. Results showed that the size and shape of particles, and the microstrucutre and hardness of partcicles were highly depended on the milling conditions. According to XRD analysis, the maximal amorphous fraction has been achieved in the air atmosphere withouth PCA milled sample (57 wt. %) powder. However the extent of Fe contamination and weight loss during milling powder resulted bigger values. As a result, the optimal combination of morphology, contamination amount and weight lost level has been observed in the case of powder milled in argon atmosphere using stearic acid.

Journal of Alloys and Compounds, 2021

Materials Science Forum, 2017

In this paper the effect of the strain path change was studied in aluminum alloy containing 0,25%... more In this paper the effect of the strain path change was studied in aluminum alloy containing 0,25% Mg. In metals alloys different metal forming processes can create strong crystallographic and morphologic texture. Both of them can cause direction dependency of the mechanical and other properties. The aim of this paper is to analyze how the effect of the increasing reduction of cold drawn wire appears as a result of the uniaxial compression performed in the direction opposite of drawing. Compression test were performed. Through the results of these tests the changes of the direction of deformations were analyzed qualitatively and numerically. These results provide the possibility to use uniaxial compression test to evaluate the mechanical behavior of cold drawn aluminum.

International Journal of Refractory Metals & Hard Materials, 2021

In the present article a 45Mo-45Cu-10Al2O3 (wt%) nano-composite was produced by mechanical alloyi... more In the present article a 45Mo-45Cu-10Al2O3 (wt%) nano-composite was produced by mechanical alloying, shaped by cold pressing then by hot pressing at 950 °C. Our aim was to investigate the effect of different ball to powder ratio (BPR) on the particle size and shape, as well as on the material composition. Investigations were done with XRD, SEM and for hot pressed specimens Brinell hardness measurement. Lower BPR resulted in nano-sized crystallites in the powder, a homogenous phase distribution and higher BPR resulted in even smaller crystallite sizes, but with ZrO2 contamination from the milling equipment. The milling resulted in two separate fractions in the metallic phases separated by crystallite size, strain and lattice parameter. After hot pressing, the lower BPR powders developed a homogeneous, evenly distributed microstructure. Cu recrystallized during hot pressing, but still remained nanocrystalline, the crystallite size of Mo and α-Al2O3 decreased even more due to crystalli...

Materials Science Forum, 2017

The production technology for automotive foundry castings has developed significantly during the ... more The production technology for automotive foundry castings has developed significantly during the past decade. The production of cylinder hats with more and more complex designs could be rather challenging for core makers. Heating might cause the annealing of the core, thus, the buoyancy of the molten metal increases which might cause the movement of the core. The heat distortion of the cores was examined with a Hot Distortion Tester. A universal Instron 5982 device was used for bending, wedge penetration strength and cold and hot compression tests. The test bars were prepared with cold- and hot-box processes using DMPA (Dimethylpropyl-amine) under laboratory conditions. The tests showed that the decrease of the bending strength is proportional to the amount of additives. The compression test results showed that the test bars produced with cold-box compression have the lowest and the ones with furan resin mixtures have the highest compressive strength.

Key Engineering Materials, 2015

In this study the bonding properties of three layer-plated aluminum sheets are investigated. The ... more In this study the bonding properties of three layer-plated aluminum sheets are investigated. The alloys applied in specific layers were as follows: AlMn1Si0.8 (core alloy) and AlSi10 (liner). The bonding was performed on a Von Roll experimental roll mill using hot rolling. The experimental temperatures were 460, 480 and 500 °C, respectively. To qualify bond development, T-peel test was used. The test was performed using an Instron universal material testing machine. T-peel test can be well used for the qualification of bond strength as the peel-off force and bond value developed on contacting surfaces are proportional. In addition to T-peel test, optical micrographs and SEM micrographs were also captured, in which typical bond faults were sought. The study aims at modelling the technology used in industry and exploring some typical bond faults as well as suggesting the causes generating these and their remedy. The impact of surface roughening before heating was studied as well. Also...

In this study the bonding properties of three layer-plated aluminum sheets are investigated. The ... more In this study the bonding properties of three layer-plated aluminum sheets are investigated. The alloys applied in specific layers were as follows: AlMn1Si0.8 (core alloy) and AlSi10 (liner). The bonding was performed on a Von Roll experimental roll mill using hot rolling. The experimental temperatures were 460, 480 and 500 °C, respectively. To qualify bond development, T-peel test was used. The test was performed using an Instron universal material testing machine. T-peel test can be well used for the qualification of bond strength as the peel-off force and bond value developed on contacting surfaces are proportional. In addition to T-peel test, optical micrographs and SEM micrographs were also captured, in which typical bond faults were sought. Furthermore in this study covers the analysis of tear-off of bond of 3-layered aluminum sheets, for dynamically hardening liner layer and less dynamically hardening core sheets. The analyses were backed by means of finite element method as well as experimental way. The tear-off of bond was tested in one pass with various reductions,

Materials Science Forum, 2013

This paper presents an investigation about the occurrence of the dynamic recrystallization (DRX) ... more This paper presents an investigation about the occurrence of the dynamic recrystallization (DRX) during hot forming. Two 7075 aluminum alloy samples in different initial states were examined by compression tests at temperatures between 573 K and 723 K and constant strain rates ranging from 0.002 to 2 (s-1) with the maximum strain of 0.5 mm/mm. The activation energies of the examined aluminium were calculated, being 137.7 kJ/mol and 142.4 kJ/mol. The critical stresses and strains for the initiation of the dynamic recrystallization were determined using a numerical method based on the changes of the work hardening rate (θ) as a function of the flow stress (σ) or a strain (ε), respectively. Based on the micrographs taken after the deformations it was revealed that in some cases only dinamyc recovery (DRV) whereas in others DRX occurred under the applied examination conditions. The critical stress which belongs to the onset of the DRX or the DRV depend on the temperature, the strain rat...

Materials Science Forum, 2015

Dynamic recrystallization (DRX) characteristics of an 5182 Al alloy was investigated at temperatu... more Dynamic recrystallization (DRX) characteristics of an 5182 Al alloy was investigated at temperatures ranging from 673 K-773 K and constant strain rates of 0.01 s-1, 0.1 s-1, 1 s-1, 10 s-1, and 50 s-1. The average grain size of the as-casted alloy was 160 μm and was refined to 20 μm via deformation at 773 K, 50 s-1 to a strain level of 0.5 (40%). The true stress-strain curves were determined and divided into two main groups based on the temperatures and strain rates. The activation energy of the DRX in the examined aluminum alloys was calculated, being 175,87 kJ/mol. During the crystallization process compound phases were crystallized along the border of initial grains due to the great content of Mg, Mn and Fe. It was deduced from the metallography examination that most of the new grains formed via necklacing mechanism from the mentioned borders during the DRX.

International Journal of Refractory Metals and Hard Materials, 2021

W and Cu can be found in separate phases in the W-Cu composites since these elements do not disso... more W and Cu can be found in separate phases in the W-Cu composites since these elements do not dissolve in each other neither in liquid nor in solid phase, but with mechanical alloying it is possible to produce nonequilibrium W-Cu alloys In this work the nanostructured W-Cu composites were produced by planetary ball milling. The nanostructured W-Cu powder was sintered on 900°C and 950°C with 50 MPa pressure applied. The meso-and microstructure of the W-Cu powder and the sintered samples, were investigated with SEM, TEM and XRD. After 50 hours of milling, the size of the W crystallites was ~ 10 nm, and about 10 % of the Cu was solved in the W matrix, producing a W-Cu nonequilibrium alloy layer on the surface of W nano crystallites. During sintering, the Cu atoms left from the W surface to the Cu phases, so the W-Cu nonequilibrium alloy layer disappeared. The size of the W crystallitesafter 60 min of sintering on 950°C-was around 170 nm, and the relative density was ~90% of the theoretical density.

IOP Conference Series: Materials Science and Engineering, Oct 18, 2018

Properties of powders made from Ti50Cu27,5Ni10Zr10Co2,5 alloy, milled under different conditions ... more Properties of powders made from Ti50Cu27,5Ni10Zr10Co2,5 alloy, milled under different conditions for only 3600 s in total were investigated. For this purpose two different milling atmospheres and two different Process Control Agents (PCA) were tested: argon without PCA, air without PCA, argon combined with stearic acid, argon combined with petroleum spirit. Results showed that the size and shape of particles, and the microstrucutre and hardness of partcicles were highly depended on the milling conditions. According to XRD analysis, the maximal amorphous fraction has been achieved in the air atmosphere withouth PCA milled sample (57 wt. %) powder. However the extent of Fe contamination and weight loss during milling powder resulted bigger values. As a result, the optimal combination of morphology, contamination amount and weight lost level has been observed in the case of powder milled in argon atmosphere using stearic acid.

Journal of Alloys and Compounds, 2021

Materials Science Forum, 2017

In this paper the effect of the strain path change was studied in aluminum alloy containing 0,25%... more In this paper the effect of the strain path change was studied in aluminum alloy containing 0,25% Mg. In metals alloys different metal forming processes can create strong crystallographic and morphologic texture. Both of them can cause direction dependency of the mechanical and other properties. The aim of this paper is to analyze how the effect of the increasing reduction of cold drawn wire appears as a result of the uniaxial compression performed in the direction opposite of drawing. Compression test were performed. Through the results of these tests the changes of the direction of deformations were analyzed qualitatively and numerically. These results provide the possibility to use uniaxial compression test to evaluate the mechanical behavior of cold drawn aluminum.

International Journal of Refractory Metals & Hard Materials, 2021

In the present article a 45Mo-45Cu-10Al2O3 (wt%) nano-composite was produced by mechanical alloyi... more In the present article a 45Mo-45Cu-10Al2O3 (wt%) nano-composite was produced by mechanical alloying, shaped by cold pressing then by hot pressing at 950 °C. Our aim was to investigate the effect of different ball to powder ratio (BPR) on the particle size and shape, as well as on the material composition. Investigations were done with XRD, SEM and for hot pressed specimens Brinell hardness measurement. Lower BPR resulted in nano-sized crystallites in the powder, a homogenous phase distribution and higher BPR resulted in even smaller crystallite sizes, but with ZrO2 contamination from the milling equipment. The milling resulted in two separate fractions in the metallic phases separated by crystallite size, strain and lattice parameter. After hot pressing, the lower BPR powders developed a homogeneous, evenly distributed microstructure. Cu recrystallized during hot pressing, but still remained nanocrystalline, the crystallite size of Mo and α-Al2O3 decreased even more due to crystalli...

Materials Science Forum, 2017

The production technology for automotive foundry castings has developed significantly during the ... more The production technology for automotive foundry castings has developed significantly during the past decade. The production of cylinder hats with more and more complex designs could be rather challenging for core makers. Heating might cause the annealing of the core, thus, the buoyancy of the molten metal increases which might cause the movement of the core. The heat distortion of the cores was examined with a Hot Distortion Tester. A universal Instron 5982 device was used for bending, wedge penetration strength and cold and hot compression tests. The test bars were prepared with cold- and hot-box processes using DMPA (Dimethylpropyl-amine) under laboratory conditions. The tests showed that the decrease of the bending strength is proportional to the amount of additives. The compression test results showed that the test bars produced with cold-box compression have the lowest and the ones with furan resin mixtures have the highest compressive strength.

Key Engineering Materials, 2015

In this study the bonding properties of three layer-plated aluminum sheets are investigated. The ... more In this study the bonding properties of three layer-plated aluminum sheets are investigated. The alloys applied in specific layers were as follows: AlMn1Si0.8 (core alloy) and AlSi10 (liner). The bonding was performed on a Von Roll experimental roll mill using hot rolling. The experimental temperatures were 460, 480 and 500 °C, respectively. To qualify bond development, T-peel test was used. The test was performed using an Instron universal material testing machine. T-peel test can be well used for the qualification of bond strength as the peel-off force and bond value developed on contacting surfaces are proportional. In addition to T-peel test, optical micrographs and SEM micrographs were also captured, in which typical bond faults were sought. The study aims at modelling the technology used in industry and exploring some typical bond faults as well as suggesting the causes generating these and their remedy. The impact of surface roughening before heating was studied as well. Also...

In this study the bonding properties of three layer-plated aluminum sheets are investigated. The ... more In this study the bonding properties of three layer-plated aluminum sheets are investigated. The alloys applied in specific layers were as follows: AlMn1Si0.8 (core alloy) and AlSi10 (liner). The bonding was performed on a Von Roll experimental roll mill using hot rolling. The experimental temperatures were 460, 480 and 500 °C, respectively. To qualify bond development, T-peel test was used. The test was performed using an Instron universal material testing machine. T-peel test can be well used for the qualification of bond strength as the peel-off force and bond value developed on contacting surfaces are proportional. In addition to T-peel test, optical micrographs and SEM micrographs were also captured, in which typical bond faults were sought. Furthermore in this study covers the analysis of tear-off of bond of 3-layered aluminum sheets, for dynamically hardening liner layer and less dynamically hardening core sheets. The analyses were backed by means of finite element method as well as experimental way. The tear-off of bond was tested in one pass with various reductions,

Materials Science Forum, 2013

This paper presents an investigation about the occurrence of the dynamic recrystallization (DRX) ... more This paper presents an investigation about the occurrence of the dynamic recrystallization (DRX) during hot forming. Two 7075 aluminum alloy samples in different initial states were examined by compression tests at temperatures between 573 K and 723 K and constant strain rates ranging from 0.002 to 2 (s-1) with the maximum strain of 0.5 mm/mm. The activation energies of the examined aluminium were calculated, being 137.7 kJ/mol and 142.4 kJ/mol. The critical stresses and strains for the initiation of the dynamic recrystallization were determined using a numerical method based on the changes of the work hardening rate (θ) as a function of the flow stress (σ) or a strain (ε), respectively. Based on the micrographs taken after the deformations it was revealed that in some cases only dinamyc recovery (DRV) whereas in others DRX occurred under the applied examination conditions. The critical stress which belongs to the onset of the DRX or the DRV depend on the temperature, the strain rat...

Materials Science Forum, 2015

Dynamic recrystallization (DRX) characteristics of an 5182 Al alloy was investigated at temperatu... more Dynamic recrystallization (DRX) characteristics of an 5182 Al alloy was investigated at temperatures ranging from 673 K-773 K and constant strain rates of 0.01 s-1, 0.1 s-1, 1 s-1, 10 s-1, and 50 s-1. The average grain size of the as-casted alloy was 160 μm and was refined to 20 μm via deformation at 773 K, 50 s-1 to a strain level of 0.5 (40%). The true stress-strain curves were determined and divided into two main groups based on the temperatures and strain rates. The activation energy of the DRX in the examined aluminum alloys was calculated, being 175,87 kJ/mol. During the crystallization process compound phases were crystallized along the border of initial grains due to the great content of Mg, Mn and Fe. It was deduced from the metallography examination that most of the new grains formed via necklacing mechanism from the mentioned borders during the DRX.