Emil Yankov | University of Ruse (original) (raw)
Papers by Emil Yankov
PubMed, 1979
Two cases of humerus varus congenitus have been treated by lengthening of the humerus using an ex... more Two cases of humerus varus congenitus have been treated by lengthening of the humerus using an external distraction device. The first was lengthened by about 6 centimetres and the second by about four centimetres. In one case, primary bone union was obtained and in the second, secondary grafting had to be done. The clinical results were satisfactory.
The present research summarises the influence of technological modes based on experimental studie... more The present research summarises the influence of technological modes based on experimental studies of steels BH11 and BH21 (BS 4659) for hot work in ion nitriding. The peculiarity is that one or several precisely defined modes are not fixed, but a group of parameters from the action of the considered technology in a planned experiment is studied. As a result, the technological modes of ion-nitrided steels are determined, corresponding to the minimal and maximal penetration of the counter-body in the nitrided layer. The obtained results are based on additional research related to microhardness and relative wear resistance. In this way a finished idea of the tribological properties of ion nitrided steels with a specialised purpose is obtained. The tools by which the problem is solved are design of experiments (DOE), modelling and single-criteria optimisation of controlled quantities. The main contribution of the paper is a formalised determination of the influence of the technological parameters of ionic nitriding on the phase composition of the nitrided zone and respectively on the wear resistance of the surface layer.
Mechanics Transport Communications - Academic journal,, 2016
2022 8th International Conference on Energy Efficiency and Agricultural Engineering (EE&AE), Jun 30, 2022
Vacuum, Aug 1, 2018
The mechanical properties and surface topography of TiN/TiO 2 coatings deposited by reactive magn... more The mechanical properties and surface topography of TiN/TiO 2 coatings deposited by reactive magnetron sputtering on electron beam surface treated Ti5Al4V substrates, has been studied. The phase composition and crystallographic orientation, studied by X-ray diffraction. The hardness was investigated by nanoindentation test. The surface topography was evaluated using atomic force microscopy. The results show that polycrystalline TiN and anatase-TiO 2 phases are present in all cases. The electron beam treatment (EBT) leads to a more symmetrical distribution of the heights in comparison with the untreated substrates, as well as to increase in the surface roughness. The hardness of the Ti5Al4V substrates before and after the electron beam treatment process increases which is due to the transformation α+β to ά martensitic microstructure occurring due to the fast cooling rate after the melting process. EBT leads to increase the surface roughness from 8 nm to 25 nm for the deposition of TiN/TiO2 coatings on Ti5Al4V. The treatment of Ti5Al4V
Materials Science Forum, Aug 31, 2022
The study presents the development of a system for measurement of the asymmetry between the human... more The study presents the development of a system for measurement of the asymmetry between the human shoulders. Such measurements are necessary in order to diagnose potential muscular imbalance and when possible, take corrective actions in the form of daily exercises. The system is based on two infrared proximity sensors, installed above the shoulders of the investigated human shoulders. A calibration procedure of the sensors and a following calibration model selection reduced the absolute error for the shoulders difference below 1.49 mm. Yet, if the measurement distance is kept within the range (40…110) mm, the accuracy is below 1 mm. The experiments also showed that the calibration is individual for each reflection surface, which should be considered during experimental measurements.
IOP conference series, Oct 26, 2018
MATEC web of conferences, 2017
IOP conference series, Oct 26, 2018
The metallic implants represent a major class of the hard tissue replacement materials. In order ... more The metallic implants represent a major class of the hard tissue replacement materials. In order to enhance the surface properties of the titanium alloys multicomponent coatings containing ceramic phases are employed to improve the tribological performance, corrosion resistance and biocompatibility. The mechanical properties (elastic modulus, necking region, loss of adhesion) of arc PVD TiN and TiN/TiO2 coatings deposited on unalloyed Ti (99 wt. %) foil were examined by nanoindentation, uniaxial tensile test while applying a new approachusing thermal imaging camera during the test. The hardness of the TiN coating reached values of 9649 MPa and 67 GPa, while that of the TiN/TiO2 was lowered down to 8774 MPa and 58.5 GPa which low values are closer to that of the cortical bone. The mechanical behavior of TiN/TiO2 coated material characterized it as a more plastic system indicating a good deformability while the TiN displayed more fragile behavior. There were no signs of loss of adhesion or loss of coating integrity up to maximum load for all tested TiN and TiN/TiO2 coated samples. Тhe thermal analysis proves that the coated samples show lower thermal conductivity, which is very important for the performance of an endosseous dental implant for example.
Materials Today: Proceedings, 2019
Abstract Aluminum thin films were deposited on mild steel substrates at substrate temperatures of... more Abstract Aluminum thin films were deposited on mild steel substrates at substrate temperatures of 80°C and 100°C at a constant sputtering power of 300 W by radio-frequency (RF) magnetron sputtering method. The films were then characterized for microstructure and mechanical properties by optical surface profiler (OSP), scanning electron microscopy (SEM), x-ray diffraction (XRD) and micro-scratch tests. The results showed that films deposited at 80°C consisted of long and layered structures with porous oxides whereas those deposited at 100°C were characterized by finer structures with porous and amorphous network of oxide-dominant structures. The XRD diffractograms revealed amorphous structures for both samples and lower roughness for samples deposited at 100°C. The behavior of the surfaces under extremely high micro-scratch loads (0-30 N) was characterized by piling up of the amorphous materials on the edges of the scratch track (100°C) and lateral and track-in cracking along the scratching direction (80°C). The results suggest the significance of substrate temperature on the adhesion characteristics of aluminum thin films.
Advanced structured materials, Dec 31, 2018
In modern mechanical engineering, there is increased need to find solutions for fast manufacturin... more In modern mechanical engineering, there is increased need to find solutions for fast manufacturing of real prototypes. One of these is the fast-growing up-to-date CAD/CAM/CAE system enabling to create digital prototypes. Using CAD systems the conceptual design is analyzed and tested before producing the real prototype. This reduces the compliance costs for manufacturing of the physical models and tooling as well as the production time of the prototype is lessened several times. With the development of technology, and especially in medicine, it is necessary to produce prototypes that can be obtained relatively quickly and meet the requirements of accuracy. Rapid prototyping technologies have such capabilities that they can reproduce digital models with their manufacturer’s precision. To determine the accuracy of printing, a SLA system is used. To determine the accuracy of printing, a SLA system is used. One of the peculiarities of making a detail by this method is the appearance of distortions in the initial stage of construction at large rectilinear plots. In order to determine the minimum printing deviations, a strategy for printing prototype models at a different slope of 0°–90° was used. Patterns are made with coordinate networks, enabling post-print deviations to be evaluated by matching the digital model. The present study will be useful in developing prototype models for micro and nanotechnology in mechanical engineering and medicine, providing a solution for their optimal location with minimal deviations.
Key Engineering Materials, Jul 1, 2019
The goal of this work is to evaluate a common final sterilization technique with EtO by measuring... more The goal of this work is to evaluate a common final sterilization technique with EtO by measuring its effect on the physicochemical properties of PVD deposited TiN/TiO2 coatings on Ti-5Al-4V alloy. As the effectiveness of EtO sterilization corresponds to the operation parameters (temperature, duration, humidity, etc.), two different exposure cycles (cool (MS) at 37 °C for 220 min gas expose and warm (SS) at 55 °C for 100 min expose) were examined. SEM analysis revealed that the surface morphology of the coatings was not changed after both MS and SS treatments. In contrast to Ti 2p and O 1s peaks determined by XPS analysis, C 1s peak of TiO2 layer decreased with increasing sterilization temperature while the percentage contribution of Ti-OH in O 1s increased. This affected the surface hydrophilicity and free energy that increased from 47.37 for the control sample to 50.77 mJ m-2 in the case of SS specimen. Additionally, EtO sterilized samples demonstrated decreased values of corrosion and passivation current densities in simulated body fluid (pH 7.4) at 37 ± 0.05 °C as opposed to the control sample. The results indicate the suitability of both mild and severe EtO sterilization methods for improvement of the desired physicochemical properties of gradient TiN/TiO2 coatings.
Laser Physics, Mar 2, 2023
Indian Journal of Engineering and Materials Sciences
AISI H10, H11, H21, and D2 have been vacuum oxy-nitrocarburizing at 570 °C in cycling gas flow ma... more AISI H10, H11, H21, and D2 have been vacuum oxy-nitrocarburizing at 570 °C in cycling gas flow manner. Metastable diagram calculations belonging to Fe-N-C and Fe-N-C-X systems (X = Cr, Mo, W), have been performed by using "phase diagram" module of FactSageto predict the steels' phase compositions. The reactive diffusion of both N and C into the tempered martensite has been discussed on the base of different chemical composition, size, and distribution of phases in the microstructure. The compound layers consisted mainly of not pre-saturated and poreless ε-carbonitride and magnetite (Fe 3 O 4). In D2 steel, nitrogen diffusion caused a complete transformation of the primary carbides in 50 μm depths from the surface affecting the growth of grain boundary carbides. In contrast to the sharp compound/diffusion layer interface of H10, H11, and D2 steels, in H21 carbon and nitrogen were deeply absorbed in the diffusion layer while chromium strongly increased underneath the surface. The vacuum process enhanced the hardness and decreased the friction coefficients down to 0.13-0.15 at 100 N normal load for all samples. Since the compound layer thickness was relatively small for all tool steels, the phase composition and structure of the diffusion layers were found to be crucial for the scratch wear performance.
Corrosion properties of diffusional zinc coatings with various surface compositions, obtained by ... more Corrosion properties of diffusional zinc coatings with various surface compositions, obtained by nanogalvanizing technology, are studied in model oilfield and aggressive chloride-containing media. A complex of physical and chemical methods for studying corrosion behavior, including polarization measurements, X-ray diffraction analysis and SEM, was used in the work. Corrosion resistance of diffusional zinc coatings obtained by nanogalvanizing is determined by the composition, texture and thickness of the coating.
Journal of Physics: Conference Series, 2020
Titanium-based vacuum coatings, such as TiN and TiO2, are being widely used for functionalization... more Titanium-based vacuum coatings, such as TiN and TiO2, are being widely used for functionalization of the surfaces and for forming protective surface layers for a number of applications. In this study, TiN/TiO2 coatings were deposited by two physical vacuum deposition (PVD) methods: cathodic-arc (for TiN) and glow-discharge (for TiO2) deposition. We studied the bilayer film composition, structure and properties by means of X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS), and scratch test analysis. The XRD spectrum indicated the presence of both anatase and rutile TiO2 phases, together with TiN reflections. The Ti 2p, O 1s and N 1s core level of XPS spectra in the depth of the oxide up to the oxide-nitride interface indicated intimate heterojunction between the layers. This results in a lower coefficient of friction and improved adhesion strength of the TiN/TiO2 film compared with pristine TiN coating.
Coatings
The aim of this research is to achieve a high-quality and long-lasting laser marking of ammunitio... more The aim of this research is to achieve a high-quality and long-lasting laser marking of ammunition, which is of interest to the defense industry. The study is about the effects of speed, raster pitch and power on the roughness and microhardness of the marked areas of copper samples. The experiments were carried out with a fiber laser and a copper bromide laser—modern lasers widely used in industrial production. Laser power, scan speed and raster step were varied to determine their effects on the resulting microhardness and surface roughness. The lasers operate in different wavelength ranges, with the optical laser operating at 1064 nm in the near-infrared region and the copper bromide laser at 511 nm and 578 nm in the visible region, allowing the influence of wavelengths on the process to be investigated. The roughness and microhardness velocity dependence for three powers and two pulse durations for the fiber laser were obtained from the experimental data. The dependence of roughne...
PubMed, 1979
Two cases of humerus varus congenitus have been treated by lengthening of the humerus using an ex... more Two cases of humerus varus congenitus have been treated by lengthening of the humerus using an external distraction device. The first was lengthened by about 6 centimetres and the second by about four centimetres. In one case, primary bone union was obtained and in the second, secondary grafting had to be done. The clinical results were satisfactory.
The present research summarises the influence of technological modes based on experimental studie... more The present research summarises the influence of technological modes based on experimental studies of steels BH11 and BH21 (BS 4659) for hot work in ion nitriding. The peculiarity is that one or several precisely defined modes are not fixed, but a group of parameters from the action of the considered technology in a planned experiment is studied. As a result, the technological modes of ion-nitrided steels are determined, corresponding to the minimal and maximal penetration of the counter-body in the nitrided layer. The obtained results are based on additional research related to microhardness and relative wear resistance. In this way a finished idea of the tribological properties of ion nitrided steels with a specialised purpose is obtained. The tools by which the problem is solved are design of experiments (DOE), modelling and single-criteria optimisation of controlled quantities. The main contribution of the paper is a formalised determination of the influence of the technological parameters of ionic nitriding on the phase composition of the nitrided zone and respectively on the wear resistance of the surface layer.
Mechanics Transport Communications - Academic journal,, 2016
2022 8th International Conference on Energy Efficiency and Agricultural Engineering (EE&AE), Jun 30, 2022
Vacuum, Aug 1, 2018
The mechanical properties and surface topography of TiN/TiO 2 coatings deposited by reactive magn... more The mechanical properties and surface topography of TiN/TiO 2 coatings deposited by reactive magnetron sputtering on electron beam surface treated Ti5Al4V substrates, has been studied. The phase composition and crystallographic orientation, studied by X-ray diffraction. The hardness was investigated by nanoindentation test. The surface topography was evaluated using atomic force microscopy. The results show that polycrystalline TiN and anatase-TiO 2 phases are present in all cases. The electron beam treatment (EBT) leads to a more symmetrical distribution of the heights in comparison with the untreated substrates, as well as to increase in the surface roughness. The hardness of the Ti5Al4V substrates before and after the electron beam treatment process increases which is due to the transformation α+β to ά martensitic microstructure occurring due to the fast cooling rate after the melting process. EBT leads to increase the surface roughness from 8 nm to 25 nm for the deposition of TiN/TiO2 coatings on Ti5Al4V. The treatment of Ti5Al4V
Materials Science Forum, Aug 31, 2022
The study presents the development of a system for measurement of the asymmetry between the human... more The study presents the development of a system for measurement of the asymmetry between the human shoulders. Such measurements are necessary in order to diagnose potential muscular imbalance and when possible, take corrective actions in the form of daily exercises. The system is based on two infrared proximity sensors, installed above the shoulders of the investigated human shoulders. A calibration procedure of the sensors and a following calibration model selection reduced the absolute error for the shoulders difference below 1.49 mm. Yet, if the measurement distance is kept within the range (40…110) mm, the accuracy is below 1 mm. The experiments also showed that the calibration is individual for each reflection surface, which should be considered during experimental measurements.
IOP conference series, Oct 26, 2018
MATEC web of conferences, 2017
IOP conference series, Oct 26, 2018
The metallic implants represent a major class of the hard tissue replacement materials. In order ... more The metallic implants represent a major class of the hard tissue replacement materials. In order to enhance the surface properties of the titanium alloys multicomponent coatings containing ceramic phases are employed to improve the tribological performance, corrosion resistance and biocompatibility. The mechanical properties (elastic modulus, necking region, loss of adhesion) of arc PVD TiN and TiN/TiO2 coatings deposited on unalloyed Ti (99 wt. %) foil were examined by nanoindentation, uniaxial tensile test while applying a new approachusing thermal imaging camera during the test. The hardness of the TiN coating reached values of 9649 MPa and 67 GPa, while that of the TiN/TiO2 was lowered down to 8774 MPa and 58.5 GPa which low values are closer to that of the cortical bone. The mechanical behavior of TiN/TiO2 coated material characterized it as a more plastic system indicating a good deformability while the TiN displayed more fragile behavior. There were no signs of loss of adhesion or loss of coating integrity up to maximum load for all tested TiN and TiN/TiO2 coated samples. Тhe thermal analysis proves that the coated samples show lower thermal conductivity, which is very important for the performance of an endosseous dental implant for example.
Materials Today: Proceedings, 2019
Abstract Aluminum thin films were deposited on mild steel substrates at substrate temperatures of... more Abstract Aluminum thin films were deposited on mild steel substrates at substrate temperatures of 80°C and 100°C at a constant sputtering power of 300 W by radio-frequency (RF) magnetron sputtering method. The films were then characterized for microstructure and mechanical properties by optical surface profiler (OSP), scanning electron microscopy (SEM), x-ray diffraction (XRD) and micro-scratch tests. The results showed that films deposited at 80°C consisted of long and layered structures with porous oxides whereas those deposited at 100°C were characterized by finer structures with porous and amorphous network of oxide-dominant structures. The XRD diffractograms revealed amorphous structures for both samples and lower roughness for samples deposited at 100°C. The behavior of the surfaces under extremely high micro-scratch loads (0-30 N) was characterized by piling up of the amorphous materials on the edges of the scratch track (100°C) and lateral and track-in cracking along the scratching direction (80°C). The results suggest the significance of substrate temperature on the adhesion characteristics of aluminum thin films.
Advanced structured materials, Dec 31, 2018
In modern mechanical engineering, there is increased need to find solutions for fast manufacturin... more In modern mechanical engineering, there is increased need to find solutions for fast manufacturing of real prototypes. One of these is the fast-growing up-to-date CAD/CAM/CAE system enabling to create digital prototypes. Using CAD systems the conceptual design is analyzed and tested before producing the real prototype. This reduces the compliance costs for manufacturing of the physical models and tooling as well as the production time of the prototype is lessened several times. With the development of technology, and especially in medicine, it is necessary to produce prototypes that can be obtained relatively quickly and meet the requirements of accuracy. Rapid prototyping technologies have such capabilities that they can reproduce digital models with their manufacturer’s precision. To determine the accuracy of printing, a SLA system is used. To determine the accuracy of printing, a SLA system is used. One of the peculiarities of making a detail by this method is the appearance of distortions in the initial stage of construction at large rectilinear plots. In order to determine the minimum printing deviations, a strategy for printing prototype models at a different slope of 0°–90° was used. Patterns are made with coordinate networks, enabling post-print deviations to be evaluated by matching the digital model. The present study will be useful in developing prototype models for micro and nanotechnology in mechanical engineering and medicine, providing a solution for their optimal location with minimal deviations.
Key Engineering Materials, Jul 1, 2019
The goal of this work is to evaluate a common final sterilization technique with EtO by measuring... more The goal of this work is to evaluate a common final sterilization technique with EtO by measuring its effect on the physicochemical properties of PVD deposited TiN/TiO2 coatings on Ti-5Al-4V alloy. As the effectiveness of EtO sterilization corresponds to the operation parameters (temperature, duration, humidity, etc.), two different exposure cycles (cool (MS) at 37 °C for 220 min gas expose and warm (SS) at 55 °C for 100 min expose) were examined. SEM analysis revealed that the surface morphology of the coatings was not changed after both MS and SS treatments. In contrast to Ti 2p and O 1s peaks determined by XPS analysis, C 1s peak of TiO2 layer decreased with increasing sterilization temperature while the percentage contribution of Ti-OH in O 1s increased. This affected the surface hydrophilicity and free energy that increased from 47.37 for the control sample to 50.77 mJ m-2 in the case of SS specimen. Additionally, EtO sterilized samples demonstrated decreased values of corrosion and passivation current densities in simulated body fluid (pH 7.4) at 37 ± 0.05 °C as opposed to the control sample. The results indicate the suitability of both mild and severe EtO sterilization methods for improvement of the desired physicochemical properties of gradient TiN/TiO2 coatings.
Laser Physics, Mar 2, 2023
Indian Journal of Engineering and Materials Sciences
AISI H10, H11, H21, and D2 have been vacuum oxy-nitrocarburizing at 570 °C in cycling gas flow ma... more AISI H10, H11, H21, and D2 have been vacuum oxy-nitrocarburizing at 570 °C in cycling gas flow manner. Metastable diagram calculations belonging to Fe-N-C and Fe-N-C-X systems (X = Cr, Mo, W), have been performed by using "phase diagram" module of FactSageto predict the steels' phase compositions. The reactive diffusion of both N and C into the tempered martensite has been discussed on the base of different chemical composition, size, and distribution of phases in the microstructure. The compound layers consisted mainly of not pre-saturated and poreless ε-carbonitride and magnetite (Fe 3 O 4). In D2 steel, nitrogen diffusion caused a complete transformation of the primary carbides in 50 μm depths from the surface affecting the growth of grain boundary carbides. In contrast to the sharp compound/diffusion layer interface of H10, H11, and D2 steels, in H21 carbon and nitrogen were deeply absorbed in the diffusion layer while chromium strongly increased underneath the surface. The vacuum process enhanced the hardness and decreased the friction coefficients down to 0.13-0.15 at 100 N normal load for all samples. Since the compound layer thickness was relatively small for all tool steels, the phase composition and structure of the diffusion layers were found to be crucial for the scratch wear performance.
Corrosion properties of diffusional zinc coatings with various surface compositions, obtained by ... more Corrosion properties of diffusional zinc coatings with various surface compositions, obtained by nanogalvanizing technology, are studied in model oilfield and aggressive chloride-containing media. A complex of physical and chemical methods for studying corrosion behavior, including polarization measurements, X-ray diffraction analysis and SEM, was used in the work. Corrosion resistance of diffusional zinc coatings obtained by nanogalvanizing is determined by the composition, texture and thickness of the coating.
Journal of Physics: Conference Series, 2020
Titanium-based vacuum coatings, such as TiN and TiO2, are being widely used for functionalization... more Titanium-based vacuum coatings, such as TiN and TiO2, are being widely used for functionalization of the surfaces and for forming protective surface layers for a number of applications. In this study, TiN/TiO2 coatings were deposited by two physical vacuum deposition (PVD) methods: cathodic-arc (for TiN) and glow-discharge (for TiO2) deposition. We studied the bilayer film composition, structure and properties by means of X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS), and scratch test analysis. The XRD spectrum indicated the presence of both anatase and rutile TiO2 phases, together with TiN reflections. The Ti 2p, O 1s and N 1s core level of XPS spectra in the depth of the oxide up to the oxide-nitride interface indicated intimate heterojunction between the layers. This results in a lower coefficient of friction and improved adhesion strength of the TiN/TiO2 film compared with pristine TiN coating.
Coatings
The aim of this research is to achieve a high-quality and long-lasting laser marking of ammunitio... more The aim of this research is to achieve a high-quality and long-lasting laser marking of ammunition, which is of interest to the defense industry. The study is about the effects of speed, raster pitch and power on the roughness and microhardness of the marked areas of copper samples. The experiments were carried out with a fiber laser and a copper bromide laser—modern lasers widely used in industrial production. Laser power, scan speed and raster step were varied to determine their effects on the resulting microhardness and surface roughness. The lasers operate in different wavelength ranges, with the optical laser operating at 1064 nm in the near-infrared region and the copper bromide laser at 511 nm and 578 nm in the visible region, allowing the influence of wavelengths on the process to be investigated. The roughness and microhardness velocity dependence for three powers and two pulse durations for the fiber laser were obtained from the experimental data. The dependence of roughne...