Maria Ormanova

Dr. Maria Ormanova


Research Focus & Metrics

Academic Career Length

11Years (2016-Present)

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

Representative Publications

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10 September 2020 in Metals
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S. ValkovS. Valkov
S. Valkov
Maria OrmanovaMaria Ormanova
Maria Ormanova
Petеr PetrovPetеr Petrov
Petеr Petrov
During the last decades, electron-beam treatment technologies (EBTT) have been widely used for surface modification of metals and alloys. The EBT methods are known as accurate and efficient. They have many advantages in comparison with the conventional techniques, such as very short technological process time, uniform distribution of the energy of the electron beam, which allows a precise control of the beam parameters and formed structure and properties of the materials, etc. Moreover, electron-beam treatment technologies are a part of the additive techniques, which are known as modern methods for manufacturing of new materials with unique functional properties. Currently, modern trends in the surface treatment of metals and alloys are based on the combination of electron-beam technologies with other methods, such as thin film deposition, plasma nitriding, etc. This approach results in a significant improvement in the surface properties of the materials which opens new potential applications and can involve them into new industrial fields. This paper aims to summarize the topics related to the manufacturing and surface treatment of metals and alloys by means of electron-beam technologies. Based on a literature review, the development and growth of EBT are considered in details. The benefits of these technologies—as well as their combination with other methods—are extensively discussed.

9 August 2024 in Sensors
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DDDimitar Dichev
Dimitar Dichev
DDDimitar Diakov
Dimitar Diakov
DDDimitar I. Diakov
Dimitar I. Diakov
S. ValkovS. Valkov
S. Valkov
Maria OrmanovaMaria Ormanova
Maria Ormanova
OKOleksandr Kupriyanov
Oleksandr Kupriyanov
This paper presents a new method for correction of dynamic errors occurring when measuring flat surfaces in the presence of mechanical effects. Mechanical effects cause inertial forces and moments that affect the moving components of measuring instruments, thereby causing dynamic errors. The study proposes a mathematical model, on the basis of which algorithms for correction of dynamic errors can be developed. The basic concept of the model is based on determining the optimal estimate in the current coordinate point on the basis of the theoretical model of the measured surface and the information from the measurement that contains errors caused by internal and external factors. Based on this model, an algorithm for real-time data processing has been developed. The algorithm works in “predictor-corrector” mode at each step of which the best estimate is obtained. The estimate is based on minimizing the variance of a random component in which the main values are formed from the accumulated statistical data of the error of the model and the measurement error. This paper presents the results of experimental studies, carried out with simulations of mechanical effects in four modes. The results confirm the high efficiency of the algorithm for high-accuracy measurement of flat surfaces in the presence of mechanical effects.

1 June 2023 in Metals
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Georgi KotlarskiGeorgi Kotlarski
Georgi Kotlarski
Darina KaishevaDarina Kaisheva
Darina Kaisheva
Maria OrmanovaMaria Ormanova
Maria Ormanova
Borislav Tsonev StoyanovBorislav Tsonev Stoyanov
Borislav Tsonev Stoyanov
VDVladimir Petrov Dunchev
Vladimir Petrov Dunchev
S. ValkovS. Valkov
S. Valkov
This work presents the results of the electron-beam welding of commercially pure α-Ti (CP-Ti) and Ti6Al4V (Ti64) alloys. The structure and mechanical properties of the formed welded joints were examined as a function of the power of the electron beam. The beam power was set to P1 = 2100 W, P2 = 1500 W, and P3 = 900 W, respectively. X-ray diffraction (XRD) experiments were performed in order to investigate the phase composition of the fabricated welded joints. The microstructure was examined by both optical microscopy, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The mechanical properties of the formed joints were studied using tensile test experiments and microhardness experiments. The results of the experiments were discussed concerning the influence of the beam power on the microstructure and the mechanical properties of the weld joints. Furthermore, the practical applicability of the present method for the welding of α-Ti and Ti64 was also discussed.

18 March 2022 in Coatings
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SRStanislava Rabadzhiyska
Stanislava Rabadzhiyska
Georgi KotlarskiGeorgi Kotlarski
Georgi Kotlarski
MSMaria Shipochka
Maria Shipochka
PRPeter Metodiev Rafailov
Peter Metodiev Rafailov
Maria OrmanovaMaria Ormanova
Maria Ormanova
S. ValkovS. Valkov
S. Valkov
In this study, we present the results of the effect of duplex surface modification of 304-L stainless steel substrates by an electron-beam treatment (EBT) and subsequent deposition of diamond-like carbon coatings on the surface roughness and corrosion behavior. During the EBT process, the beam power was varied from 1000 to 1500 W. The successful deposition of the DLC coatings was confirmed by FTIR and Raman spectroscopy experiments. The results showed a presence of C–O, C=N, graphite-like sp2, and mixed sp2-sp3 C–C bond vibrations. The surface topography was studied by atomic force microscopy. The rise in the beam power leads to a decrease in the surface roughness of the deposited DLC coatings. The studies on the corrosion resistance of the samples have been performed using three electrochemical techniques: open circuit potential (OCP), cyclic voltammetry (polarization measurements), and non-destructive electrochemical impedance spectroscopy (EIS). The measured corrosion potentials suggest that these samples are corrosion-resistant even in a medium, containing corrosive agents such as chloride ions. It can be concluded that the most corrosion-resistant specimen is DLC coating deposited on electron-beam-treated 304-L SS substrate by a beam power of 1500 W.

9 July 2023 in Metals
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Angel Petrov AnchevAngel Petrov Anchev
Angel Petrov Anchev
Darina KaishevaDarina Kaisheva
Darina Kaisheva
Georgi KotlarskiGeorgi Kotlarski
Georgi Kotlarski
VDVladimir Petrov Dunchev
Vladimir Petrov Dunchev
Borislav Tsonev StoyanovBorislav Tsonev Stoyanov
Borislav Tsonev Stoyanov
S. ValkovS. Valkov
S. Valkov
This work presents the results of an investigation into the influence of beam offset on the structure and mechanical properties of electron-beam-welded joints between Ti6Al4V and Al6082-T6 alloys. The experimental procedure involved the use of specific technological conditions: an accelerating voltage of 60 kV, an electron beam current of 35 mA, a specimen motion speed of 10 mm/s, and a beam offset of 0.5 mm towards both alloys, as well as welding without an offset. The phase composition of the joints was analyzed using X-ray diffraction (XRD). The microstructure and chemical composition of the seams were studied by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The results obtained for the structure of the joints show that the beam offset has a significant influence on the structure. The microhardness was studied by means of the Vickers method. The results for the microstructure showed that the welding procedure without offset and with an offset towards the Ti alloy leads to inhomogeneous welded joints with a significant amount of intermetallics. The offset towards the Al alloy leads to the formation of a narrow area of TiAl3 phase. The measured microhardness corresponds to the increased amount of intermetallics in the case of offset towards the Ti alloy, with which the highest values were presented (about 58% higher than with Ti6Al4V plate). The results obtained for tensile properties show that the offset to the Al6082-T6 alloy leads to the highest values of tensile strength (TS) and yield strength (YS), which are twice higher than in welding without offsetting of the electron beam.

5 August 2021 in Metals
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S. ValkovS. Valkov
S. Valkov
DDDimitar Dechev
Dimitar Dechev
NINikolay Ivanov
Nikolay Ivanov
RBRuslan Bezdushnyi
Ruslan Bezdushnyi
Maria OrmanovaMaria Ormanova
Maria Ormanova
Petеr PetrovPetеr Petrov
Petеr Petrov
In this study, we present the results of Young’s modulus and coefficient of friction (COF) of Ti–Ta surface alloys formed by electron-beam surface alloying by a scanning electron beam. Ta films were deposited on the top of Ti substrates, and the specimens were then electron-beam surface alloyed, where the beam power was varied from 750 to 1750 W. The structure of the samples was characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). Young’s modulus was studied by a nanoindentation test. The coefficient of friction was studied by a micromechanical wear experiment. It was found that at 750 W, the Ta film remained undissolved on the top of the Ti, and no alloyed zone was observed. By an increase in the beam power to 1250 and 1750 W, a distinguished alloyed zone is formed, where it is much thicker in the case of 1750 W. The structure of the obtained surface alloys is in the form of double-phase α’and β. In both surface alloys formed by a beam power of 1250 and 1750 W, respectively, Young’s modulus decreases about two times due to different reasons: in the case of alloying by 1250 W, the observed drop is attributed to the larger amount of the β phase, while at 1750 W is it due to the weaker binding forces between the atoms. The results obtained for the COF show that the formation of the Ti–Ta surface alloy on the top of Ti substrate leads to a decrease in the coefficient of friction, where the effect is more pronounced in the case of the formation of Ti–Ta surface alloys by a beam power of 1250 W.