Fatme Padikova

Dr. Fatme Padikova

orcid

Research Focus & Metrics

Academic Career Length

4Years (2023-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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22 February 2024 in Coatings
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S. ValkovS. Valkov
S. Valkov
Georgi KotlarskiGeorgi Kotlarski
Georgi Kotlarski
SPStoyan Parshorov
Stoyan Parshorov
Maria OrmanovaMaria Ormanova
Maria Ormanova
Borislav Tsonev StoyanovBorislav Tsonev Stoyanov
Borislav Tsonev Stoyanov
IPIvan Parshorov
Ivan Parshorov
In the present work, we present results on the influence of electron beam surface modification on the resistance to plastic deformation and plasticity of Inconel alloy 625. During the treatment procedure, the electron beam currents were 10 and 20 mA, corresponding to beam powers of 600 W and 1200 W. The structures of the modified specimens were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The nanohardness and Young’s modulus were studied through nanoindentation experiments. The plasticity of the treated materials as well as of the untreated ones was studied through an evaluation of H3/E2, which points to resistance to plastic deformation. The results obtained show that the electron beam surface modification procedure leads to a reorientation of microvolumes and the formation of a preferred crystallographic orientation. The surface treatment of the samples using an electron beam with a power of 600 W did not lead to major changes in the structures of the samples. However, the use of a beam with a power of 1200 W led to the formation of a clearly separated modified zone with a thickness in the range of 13 to 15 μm. The Young’s modulus increased from about 100 to 153 GPa in the case of electron beam surface modification using the lower-power electron beam. The application of the higher-power electron beam did not lead to a significant change in the modulus of elasticity as compared to the untreated specimen. Also, it was found that the treatment procedure pointed to a decrease in nanohardness when the maximum power of the electron beam was applied. The resistance to plastic deformation, i.e., the H3/E2 ratio, showed that the ratio decreased significantly in both cases of electron beam surface modification, pointing to an improvement in the plasticity of the surface of the Inconel alloy 625.

19 May 2023 in Coatings
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S. ValkovS. Valkov
S. Valkov
Daniela Gospodinova NedevaDaniela Gospodinova Nedeva
Daniela Gospodinova Nedeva
VDVladimir Petrov Dunchev
Vladimir Petrov Dunchev
FPFatme Padikova
Fatme Padikova
Maria OrmanovaMaria Ormanova
Maria Ormanova
NNNikolay Nedyalkov
Nikolay Nedyalkov
In this study, the possibilities for modification and improvement of the surface structure and properties of titanium substrates by a formation of composite Ti/TiC layers are presented. The layers were fabricated by a two-step electron-beam surface modification technique. The first step consists of injection of C powder within the pure Ti substrates by electron-beam alloying technology. The second step is the refinement and homogenization of the microstructure by the electron-beam remelting procedure. During the remelting, the speed of the motion of the samples was varied, and two (most representative) velocities were chosen: 5 and 15 mm/s. Considering both speeds of the motion of the specimens, a composite structure in the form of fine TiC particles distributed within the base titanium matrix was formed. The remelting speed of 5 mm/s led to the formation of a much thicker composite layer, where the TiC particles were significantly more homogeneously distributed. The results obtained for the Vickers microhardness exhibit a significant increase in the value in the mentioned mechanical characteristic in comparison with the base Ti substrate. In the case of the lower speed of the motion of the specimen during the remelting procedure, the microhardness is 510 HV, or about 2.5 times higher than that of the titanium substrate. The application of a higher speed of the specimen motion leads to a decrease in the microhardness in comparison with the case of lower velocity. However, it is still much higher than that of the base Ti material. The mean microhardness of the sample obtained by the remelting speed of motion of 15 mm/s is 360 HV, or it is 1.8 times higher than that of the base material.

14 November 2023 in Coatings
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FPFatme Padikova
Fatme Padikova
Daniela Gospodinova NedevaDaniela Gospodinova Nedeva
Daniela Gospodinova Nedeva
VDVladimir Petrov Dunchev
Vladimir Petrov Dunchev
Borislav Tsonev StoyanovBorislav Tsonev Stoyanov
Borislav Tsonev Stoyanov
Maria OrmanovaMaria Ormanova
Maria Ormanova
S. ValkovS. Valkov
S. Valkov
This study shows the possibility of the fabrication of titanium borides by an alloying of a titanium substrate with boron powder via a scanning electron beam. During the electron beam alloying experiments, the speed movement of the specimens was varied, where it was 4 and 6 mm/s. The thickness of the alloyed zone formed by the lower velocity of the movement of the workpiece is greater than that of the coating obtained by the higher speed movement. The phase composition of the coatings is in the form of the TiB2 phase, as well as some amount of undissolved boron in both considered cases. In the case of the lower speed of the movement of the sample, the undissolved boron is within the whole volume of the alloyed zone, while at the higher speed movement, it is on the top of the specimen. The hardness of the obtained coatings by the higher speed of the specimen movement reached values of about 4500 HV. Considering the values of the surface alloy fabricated via the lower velocity movement of 4 mm/s, it is about 2600 HV, which is lower than that of the one obtained by the 6 mm/s speed of the sample movement. The result obtained for the friction coefficient (COF) for the specimen alloyed by the speed of the specimen motion of 4 mm/s is 0.40; the value for the coating obtained at a speed movement of 6 mm/s is 0.34. In both cases, these values are lower than that of the titanium substrate.

17 April 2025 in Coatings
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S. ValkovS. Valkov
S. Valkov
Georgi KotlarskiGeorgi Kotlarski
Georgi Kotlarski
SPStoyan Parshorov
Stoyan Parshorov
Maria OrmanovaMaria Ormanova
Maria Ormanova
FPFatme Padikova
Fatme Padikova
IPIvan Parshorov
Ivan Parshorov
In this work, we present results on the impact of electron beam surface modification on the phase composition, microstructure, chemical composition, and mechanical properties of Fe-Ni-Cr-Mo-W high-entropy alloy. During the experiments, the beam power was 600 and 1200 W. The phase composition was studied using XRD measurements. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were used to analyze the microstructure and chemical composition, respectively. The results showed that at the lower value of the power of the electron beam, a distinguished modified zone cannot be observed. With an increase in the discussed technological parameter, a treated zone with a thickness of about 30 μm can be seen on the top of the sample. The modulus of elasticity on the surface of the unprocessed alloy was measured to be 130 GPa and increased to 156 GPa in the case of both technological regimes of the electron beam surface modification process. The hardness on the top of the untreated alloy was about 4.5 GPa and reduced to about 3 GPa in the case of electron beam treatment on the alloy with a beam power of 600 W. The application of the modification process with a higher value of beam power, 1200 W, led to an even further decrease in the hardness, to about 2.8 GPa. The resistance to plastic deformation of the surface of the considered specimens was also analyzed via the H3/E2 ratio, and the results show that the application of the treatment procedure leads to a decrease in the resistance to plastic deformation in both cases. This decrease is more pronounced in the case of the treatment with the higher value of power of the electron beam.

17 June 2025 in Materials
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NNNikolay Nedyalkov
Nikolay Nedyalkov
Nadya Evgenieva StankovaNadya Evgenieva Stankova
Nadya Evgenieva Stankova
FPFatme Padikova
Fatme Padikova
S. ValkovS. Valkov
S. Valkov
GAGenoveva Atanasova
Genoveva Atanasova
LALyubomir Aleksandrov
Lyubomir Aleksandrov
The purpose of this work is to demonstrate that laser-induced conductive tracts in AlN ceramic can be applied for fabrication of an integrated resistive heating element. Nanosecond laser processing at a wavelength of 1064 nm of ceramic in vacuum is used for a formation of conductive areas. It is demonstrated that the applied laser fluence and the number of pulses influence strongly the electrical properties of the material in the irradiated zone. The resistance value of the produced tracks with a length of about 4 mm and width of about 1 mm may vary from 17 to about 2000 Ohms, depending on the processing conditions. The material in the processed zone is characterized by means of surface composition, morphology, and electric properties. It is found that the electrical conductivity of the formed structure is based on the ceramic decomposition and formation of aluminum layer. The analysis of the influence of the temperature on the electrical resistance value shows that the material’s conductivity could be preserved after annealing, as in the present study it is confirmed up to 300 °C. The ability of the formed tracks to serve as a basis element of ceramic integrated resistive heater is studied by applying DC voltage. It is found that the fabricated element can be used with a high reliability to about 90 °C without special requirements for contact design and encapsulation. Operation at higher temperatures is also demonstrated as the maximal one achieved is about 150 °C at 10V. The performance of the heater is investigated and discussed as the operation range is defined. The proposed element can be a basis for a design of an integrated heater in ceramic with high stability and applications in everyday life and research.

16 August 2026 in Coatings
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IIIvana Ilievska
Ivana Ilievska
FPFatme Padikova
Fatme Padikova
Georgi KotlarskiGeorgi Kotlarski
Georgi Kotlarski
ELEdmon Lazarov
Edmon Lazarov
Borislav Tsonev StoyanovBorislav Tsonev Stoyanov
Borislav Tsonev Stoyanov
S. ValkovS. Valkov
S. Valkov
Ti–Nb alloys are widely recognized as highly promising materials for orthodontic applications due to their excellent functional properties, including superior biocompatibility and a relatively low Young’s modulus that better matches that of human bone. The formation of Ti–Nb surface alloys or surface-modified layers is particularly attractive, as the surface properties of biomedical materials strongly influence their mechanical and biological interactions during service. In the present study, Ti-Nb coatings were fabricated on commercially pure titanium substrates using an electron beam surface treatment (EBST) technique. Initially, a 1 μm thick Nb layer was deposited onto the Ti substrates by direct current (DC) magnetron sputtering. Subsequently, the samples were modified through scanning electron beam irradiation, with beam power varied between 1000 and 2000 W to promote Ti-Nb alloyed layers. The phase composition of the resulting structures was analyzed by X-ray diffraction (XRD). Microstructural characteristics and chemical composition were examined using scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS). Mechanical properties were evaluated in terms of hardness and Young’s modulus. The findings of this study demonstrate the feasibility of tailoring the structural and mechanical properties of Ti–Nb surface alloys through controlled electron-beam processing and support their further investigation for potential orthodontic and dental applications.