B. Kocsis

57204633073

Publications - 13

INVESTIGATION OF HEAT-AFFECTED ZONES OF THERMITE RAIL WELDINGS

Szabolcs Fischer Mykola Sysyn Dmytro Kurhan B. Kocsis Dóra Harangozó Dalma Németh András Brautigam

Publication Name: Facta Universitatis Series Mechanical Engineering

Publication Date: 2024-12-01

Volume: 22

Issue: 4

Page Range: 689-710

Description:

The paper investigates the heat-affected zone (HAZ) of several rail joints executed by thermite rail welding (TW). The examined rail profile was 54E1 (UIC54). The rail steel categories were different: R260 and R400HT. The welding portions of the TWs fitted R350HT and R260 rail categories with normal welding gaps. The rail pieces were brand new, i.e., without any usage in the railway track. The authors executed Vickers-hardness tests (HV10) and material texture tests on the running surface of the rail head, as well as on slices cut from the rail head. The cutting was performed by the water jet method, five longitudinal direction slices with vertical cutting lines. The considered specimen lengths were 2×70 mm (i.e., 70 mm from the mid-point of the rail joint), however, the depths were 20 mm from the running surface. Therefore, the measuring spaces were 5 mm lengthwise and 2 mm in depth. The variation of the hardness values was determined considering the microstructures of the base steel material and the TW. For comparison, previously measured Elektrothermit SoW-5 and earlier own research were taken into consideration.

Open Access: Yes

DOI: 10.22190/fume221217008f

Frequency- and Temperature-Dependent Uncertainties in Hysteresis Measurements of a 3D-Printed FeSi wt6.5% Material

Tamas Orosz B. Kocsis

Publication Name: Sensors

Publication Date: 2024-05-01

Volume: 24

Issue: 9

Page Range: Unknown

Description:

Additive manufacturing of soft magnetic materials is a promising technology for creating topologically optimized electrical machines. High-performance electrical machines can be made from high-silicon-content FeSi alloys. Fe-6.5wt%Si material has exceptional magnetic properties; however, manufacturing this steel with the classical cold rolling methodology is not possible due to the brittleness of this material. Laser powder bed fusion technology (L-PBF) offers a solution to this problem. Finding the optimal printing parameters is a challenging task. Nevertheless, it is crucial to resolve the brittleness of the created materials so they can be used in commercial applications. The temperature dependence of magnetic hysteresis properties of Fe-6.5wt%Si materials is presented in this paper. The magnetic hysteresis properties were examined from 20 °C to 120 °C. The hysteresis measurements were made by a precision current generator–based hysteresis measurement tool, which uses fast Fourier transformation–based filtering techniques to increase the accuracy of the measurements. The details of the applied scalar hysteresis sensor and the measurement uncertainties were discussed first in the paper; then, three characteristic points of the static hysteresis curve of the ten L-PBF-manufactured identical toroidal cores were investigated and compared at different temperatures. These measurements show that, despite the volumetric ratio of the porosities being below 0.5%, the mean crack length in the samples is not significant for the examined samples. These small defects can cause a significant 5% decrement in some characteristic values of the examined hysteresis curve.

Open Access: Yes

DOI: 10.3390/s24092738

Water-Insoluble, Thermostable, Crosslinked Gelatin Matrix for Soft Tissue Implant Development

István Hornyák I. Zsoldos Sara Cruciani Róbert Várdai B. Kocsis Renzo Pala Viktória Varga László Smeller

Publication Name: International Journal of Molecular Sciences

Publication Date: 2024-04-02

Volume: 25

Issue: 8

Page Range: Unknown

Description:

In this present study, the material science background of crosslinked gelatin (GEL) was investigated. The aim was to assess the optimal reaction parameters for the production of a water-insoluble crosslinked gelatin matrix suitable for heat sterilization. Matrices were subjected to enzymatic degradation assessments, and their ability to withstand heat sterilization was evaluated. The impact of different crosslinkers on matrix properties was analyzed. It was found that matrices crosslinked with butanediol diglycidyl ether (BDDE) and poly(ethylene glycol) diglycidyl ether (PEGDE) were resistant to enzymatic degradation and heat sterilization. Additionally, at 1 v/v % crosslinker concentration, the crosslinked weight was lower than the starting weight, suggesting simultaneous degradation and crosslinking. The crosslinked weight and swelling ratio were optimal in the case of the matrices that were crosslinked with 3% and 5% v/v BDDE and PEGDE. FTIR analysis confirmed crosslinking, and the reduction of free primary amino groups indicated effective crosslinking even at a 1% v/v crosslinker concentration. Moreover, stress–strain and compression characteristics of the 5% v/v BDDE crosslinked matrix were comparable to native gelatin. Based on material science measurements, the crosslinked matrices may be promising candidates for scaffold development, including properties such as resistance to enzymatic degradation and heat sterilization.

Open Access: Yes

DOI: 10.3390/ijms25084336

3D printing parameters optimization for Fe-6.5 wt%Si

Lajos Károly Varga B. Kocsis Márk Windisch István Mészáros

Publication Name: Journal of Magnetism and Magnetic Materials

Publication Date: 2024-02-15

Volume: 592

Issue: Unknown

Page Range: Unknown

Description:

Optimization of 3D printing parameters was studied for the difficult to print, brittle Fe-6.5 wt%Si, applying powder bed fusion (PBF) technology. Printing orientation, volumetric energy density (VED), built plate (BP) temperature, as deposition parameters and the influence of post-deposition heat treatment (HT), were investigated. The optimal parameters were established based on the EBSD figures of samples deposited in different orientations, optical microscopy images, CT measurements, DC hysteresis curves, complex permeability spectra, and XRD patterns.

Open Access: Yes

DOI: 10.1016/j.jmmm.2024.171829

Iron Loss Calculation Methods for Numerical Analysis of 3D-Printed Rotating Machines: A Review

Miklós Kuczmann Tamas Orosz Balázs Tóth B. Kocsis Tamás Horváth

Publication Name: Energies

Publication Date: 2023-09-01

Volume: 16

Issue: 18

Page Range: Unknown

Description:

Three-dimensional printing is a promising technology that offers increased freedom to create topologically optimised electrical machine designs with a much smaller layer thickness achievable with the current, laminated steel-sheet-based technology. These composite materials have promising magnetic behaviour, which can be competitive with the current magnetic materials. Accurately calculating the iron losses is challenging due to magnetic steels’ highly nonlinear hysteretic behaviour. Many numerical methodologies have been developed and applied in FEM-based simulations from the first introduced Steinmetz formulae. However, these old curve-fitting-based iron loss models are still actively used in modern finite-element solvers due to their simplicity and high computational demand for more-accurate mathematical methods, such as Preisach- or Jiles–Atherton-model-based calculations. In the case of 3D-printed electrical machines, where the printed material can have a strongly anisotropic behaviour and it is hard to define a standardised measurement, the applicability of the curve-fitting-based iron loss methodologies is limited. The following paper proposes an overview of the current problems and solutions for iron loss calculation and measurement methodologies and discusses their applicability in designing and optimising 3D-printed electrical machines.

Open Access: Yes

DOI: 10.3390/en16186547

3D printed metal-insulator layered structure

L. K. Varga István Hatos B. Kocsis

Publication Name: Journal of Magnetism and Magnetic Materials

Publication Date: 2022-12-01

Volume: 563

Issue: Unknown

Page Range: Unknown

Description:

Additively manufactured metal–insulator layered structures are facing a contradictory demand. Laser sources with different wavelength are required to melt the two materials. In the present study we attempt to additively manufacture metal–insulator composite using a fiber laser. Three different procedures are presented. Firstly, production of a core–shell soft magnetic composite by laser-powder bed fusion technology from a unique amorphous alloy. Lastly the preparation of Fe-Si and Fe-TiN layered structure is discussed. Further improvement of Fe-TiN can be achieved by oxidation heat-treatment. Microstructure, porosity and complex permeability spectra were studied.

Open Access: Yes

DOI: 10.1016/j.jmmm.2022.169994

Development of High-Entropy Alloy Coating by Additive Technology

L. K. Varga B. Kocsis Gábor Gulyás

Publication Name: Frontiers in Materials

Publication Date: 2022-01-18

Volume: 8

Issue: Unknown

Page Range: Unknown

Description:

In this research study, various additively fabricated coatings and bulk 3D-printed parts were prepared, using the mechanical and corrosion-resistant properties of CrMnFeCoNi (Cantor alloy) and AlCrMnFeNi high-entropy alloys (HEAs). The coatings were applied to an EN 1.0038 carbon steel substrate using direct metal laser sintering. We attempted to optimize the 3D printing parameters of HEA alloys. The effect of volumetric energy density (VED) on the microstructure was investigated by scanning electron microscopy. We also examined the change of relative concentration of alloys in the direction of 3D printing (z-axis) as well as the volumetric failures (cracks and gaps). Standard salt spray tests were performed to test the corrosion resistance of various coatings after 3D printing. The use of both raw materials applied as thick films was successful; they retained their corrosion-resistant properties even with a change in their composition. Regarding the crystal structure, no difference was found between the base material and the material applied as a coating on the basis of X-ray diffraction investigations. Bulk HEA printing experiments need further optimization concerning their structural integrity and density in the case of the Cantor alloy. Bulk 3D printing experiments of the AlCrMnFeNi alloy did not yield satisfactory results because of the formation of dendritic microstructure and brittle BCC phase, and the residual internal stress resulted in part distortion and improper printing.

Open Access: Yes

DOI: 10.3389/fmats.2021.802076

Investigation of the Effects of Thermit Welding on the Mechanical Properties of the Rails

Szabolcs Fischer B. Kocsis Dóra Harangozó Vivien Barna András Brautigam

Publication Name: Acta Polytechnica Hungarica

Publication Date: 2022-01-01

Volume: 19

Issue: 3

Page Range: 37-49

Description:

This current paper deals with the investigation of the variation of the hardness of the rail steel material in the heat-affected zone (HAZ) of a rail joint made by thermit welding (TW). The tested rail is a normal R260 type rail steel category; its production date is 1977, the rolling mill was Diosgyor (Hungary), rail profile is MÁV 48.5. This rail has not been in railway track before the test. The authors performed hardness tests on the rail head’s surface even after the rail welding, as well. After the welding and hardness tests, the rail joint was cut with +/–200 mm by a rail cutter and transported to the laboratory. Water jet cutting was applied to shape six longitudinal direction slices with five vertical cutting lines from the rail piece’s head. The slices’ length was 400 mm, the width of these slices was approx. 10 mm; the TW rail joint was in the mid-point of the slices. Micro-Vickers (HV10) hardness tests were executed on these slices, in the –150…+150 mm interval lengthwise and in the 3, 6, and 10 mm depth points below the rail head’s top surface. As a result, the authors received a very detailed hardness functions of the HAZ of rail joint made by TW. These variation functions were compared to the official Elektrothermit’s SoW-5 hardness tests’ results. It can be concluded that the variation of the hardness of rail steel in the area of the HAZ correlated with the Elektrothermit’s results; however, there were some critical points where significant differences were able to be found. The highest deviation was concluded in 50 mm distance measured from the axis of welded rail joint. The authors gave possible valuable explanations for these phenomena.

Open Access: Yes

DOI: DOI not available

Preparation of soft magnetic composite from Fe-6.9wt%Si by different heat treatment strategies.

I. Zsoldos L. K. Varga B. Kocsis

Publication Name: Iop Conference Series Materials Science and Engineering

Publication Date: 2020-08-25

Volume: 903

Issue: 1

Page Range: Unknown

Description:

Present study investigated the effect of isothermal heat treatment strategies between 800 °C and 1150 °C on the magnetic properties of toroidal samples made from Fe-6.9wt%Si powder. The samples were prepared by classical powder metallurgy method since the classical sheet forming methods no longer work with the high silicon content. Our results presented here are part of a series of comparative experiments where we study the effectiveness of the insulating layers created during and before the compacting of soft magnetic composites (SMCs). Our goal was to create a soft magnetic composite made of ferromagnetic and inorganic insulating material with a frequency limit already in the megahertz range and a Snoek limit of few gigahertz. In the case of samples made from Fe-6.9wt%Si powder, the computed tomography results showed that significant porosity is to be expected after pressing. Its positive effect occurred during the heat treatment in the atmospheric agent, where silicon is precipitated and deposited on the surface of the particle. This coating is an electrically insulating layer at the grain boundaries. Depending on the heat treatment strategy, 1 or 2 ferromagnetic phases were observed. The frequency limit approached the target values, but due to the low value of static permeability, the Snoek limit did not reach the gigahertz range. However, there is a significant improvement in magnetic properties compared to the heat-treated samples in a protective gas.

Open Access: Yes

DOI: 10.1088/1757-899X/903/1/012042

Metallographic and magnetic analysis of direct laser sintered soft magnetic composites

I. Fekete L. K. Varga B. Kocsis

Publication Name: Journal of Magnetism and Magnetic Materials

Publication Date: 2020-05-01

Volume: 501

Issue: Unknown

Page Range: Unknown

Description:

In this present study, soft magnetic composite samples were made from iron-silicon alloys. For the purpose of optimizing 3D printing parameters, preliminary experiments were performed. Metallographic and computed tomography investigations were used to determine the appropriate sintering settings. Besides the microscopic and CT analysis, considering the permeability spectra have been compared to the samples.

Open Access: Yes

DOI: 10.1016/j.jmmm.2020.166425

Soft Magnetic Composites Prepared by 3D Laser Printing

I. Fekete L. K. Varga István Hatos B. Kocsis

Publication Name: Acta Physica Polonica A

Publication Date: 2020-01-01

Volume: 137

Issue: 5

Page Range: 886-888

Description:

In this study, iron and inorganic insulator powders have been used for preparing soft magnetic metal-insulator type composites by 3D laser printing. These samples have been compared with those obtained by traditional pressing and sintering method. Considering the permeability spectra, an increase of the frequency limit has been found for the laser printed samples. In addition to the AC and DC magnetic parameters, the results of XRD and SEM investigations are also presented.

Open Access: Yes

DOI: 10.12693/APhysPolA.137.886

Conformal cooling with heat-conducting inserts by direct metal laser sintering

István Hatos B. Kocsis H. Hargitai

Publication Name: Iop Conference Series Materials Science and Engineering

Publication Date: 2018-11-30

Volume: 448

Issue: 1

Page Range: Unknown

Description:

With the development of layer manufacturing technologies injection mold inserts with conformal cooling channels can be manufactured. If the cooling channels can be placed along the geometry, the heat removal is uniform and effective. In tight mold regions, formation of cooling channel is not possible or not efficient. The combination of conformal cooling and heat conductive insert can be an ideal solution for the effective cooling.

Open Access: Yes

DOI: 10.1088/1757-899X/448/1/012027

Effect of locally increased melted layer thickness on the mechanical properties of laser sintered tool steel parts

I. Fekete T. Ibriksz István Hatos András Lajos Nagy B. Kocsis H. Hargitai

Publication Name: Iop Conference Series Materials Science and Engineering

Publication Date: 2018-10-18

Volume: 426

Issue: 1

Page Range: Unknown

Description:

Additive technologies have several advantages over conventional manufacturing, such as the freedom of geometry of the products and internal structures. There are also some limitations and problems, deriving from stopping the process during the production. By restarting the process, the building often continues with a thicker starting layer due to the deposition of two or more layers. The effect of skipped melting of layers is investigated in this paper. Maraging steel powder (MS1) was used in direct metal laser sintering (DMLS) process to produce samples with increased thickness of melted layers. The layer thickness was increased in 20 μm steps up to 160 μm with 0.5 mm offset between the increased thickness layers. Porosity caused by the uneven melting was measured by optical microscope, mechanical tests were carried out to quantify the effect of skipped layers and fractured surfaces were observed under SEM. We have found that the yield strength and tensile strength are not affected if the layer thickness is slightly increased locally in the laser sintered part, while even a small increase in porosity greatly reduces the total elongation of the specimen. The decrease of impact energy due to the porosities shows similar correlation with the decrease of percentage elongation at break. However, the Charpy impact test is much more sensitive to layer skipping, the lack of melted layers lowers the impact strength significantly.

Open Access: Yes

DOI: 10.1088/1757-899X/426/1/012014