Vladimir Todorov

Technical University of Gabrovo

*This is an algorithmically generated author record based on publicly available information.

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Technical University of Gabrovo

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Vladimir Todorov has a total of 14 co-authors. Here are the top co-authors by number of shared publications:

Vladimir Dunchev
Department Material Science and Mechanics of Materials, Technical University of Gabrovo, 5300 Gabrovo, Bulgaria
3 shared publications
Galya Duncheva
Department of Material Science and Mechanics of Materials, Technical University of Gabrovo, 5300 Gabrovo, Bulgaria
2 shared publications
Kalin Anastasov
Center of Competence “Smart Mechatronic, Eco- and Energy-Saving Systems and Technologies”, Technical University of Gabrovo, 5300 Gabrovo, Bulgaria
2 shared publications
Milka Atanasova
Department of Material Science and Mechanics of Materials, Technical University of Gabrovo, 5300 Gabrovo, Bulgaria
2 shared publications
Yaroslav Argirov
Department of Material Sciences, Technical University of Varna, 9010 Varna, Bulgaria
2 shared publications
Angel Anchev
Department of Material Science and Mechanics of Materials, Technical University of Gabrovo, 5300 Gabrovo, Bulgaria
1 shared publication

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- 22 May 2026
- Published by MDPI AG in Materials
Effects of Heat Treatment Procedures and Diamond Burnishing on Tensile Properties and Surface Integrity of Additively Manufactured 17-4PH Steel Cylindrical Parts
by Galya Duncheva, Jordan Maximov, Vladimir Dunchev, Angel Anchev, Vladimir Todorov, Yaroslav Argirov, Kalin Anastasov, Hristian Mitev
This article presents a new combined post-processing concept to improve the quality of laser powder bed fusion (LPBF) of 17-4PH stainless steel (SS) cylindrical parts fabricated from N₂-atomised LaserForm 17-4PH (B) powder. The concept is based on consecutive heat treatment procedures and diamond burnishing (DB) processes. A two-stage study was conducted. The first stage was an LPBF process experiment. The following combination of LPBF parameter values was selected after optimisation: a laser power of $P = 150 W$ , laser scanning speed of v = 1200 mm/s, and layer thickness of $t = 40 μ m$ . In the second stage, this combination was used to evaluate the effects of two heat treatment procedures (HT1 and HT2) and two DB processes (using burnishing forces of 100 N and 300 N) on the tensile properties and surface integrity of LPBF 17-4PH SS cylindrical samples. The HT2 procedure, including annealing $(1200^{\circ}$ , $4 h)$ , solution treatment ( $1060^{\circ}$ , $1 h)$ , cooling ( ${- 70}^{\circ} C, 2 h$ ), and ageing ( $482^{\circ}$ , $4 h$ ) led to yield limit, tensile strength, and Vickers hardness values of $Y L = 1071 M P a$ , $T S = 1410 M P a$ , and $523 H V,$ respectively. The concept presented takes advantage of the combination of the transformation, precipitation and strain-hardening effects. The combined effect was most pronounced in the samples subjected to the HT2 procedure and subsequent DB (300 N), for which a retained austenite fraction of 6.93%, surface microhardness of ${563 H V}_{0.05}$ and the maximum values of the compressive axial and hoop RSs of $- 1426.3 M P a$ and $- 1095.9 M P a$ , respectively, were measured.
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- 22 May 2026
- Published by MDPI AG in Materials
Open Access
Effects of Heat Treatment Procedures and Diamond Burnishing on Tensile Properties and Surface Integrity of Additively Manufactured 17-4PH Steel Cylindrical Parts
by Galya Duncheva, Jordan Maximov, Vladimir Dunchev, Angel Anchev, Vladimir Todorov, Yaroslav Argirov, Kalin Anastasov, Hristian Mitev
This article presents a new combined post-processing concept to improve the quality of laser powder bed fusion (LPBF) of 17-4PH stainless steel (SS) cylindrical parts fabricated from N₂-atomised LaserForm 17-4PH (B) powder. The concept is based on consecutive heat treatment procedures and diamond burnishing (DB) processes. A two-stage study was conducted. The first stage was an LPBF process experiment. The following combination of LPBF parameter values was selected after optimisation: a laser power of $P = 150 W$ , laser scanning speed of v = 1200 mm/s, and layer thickness of $t = 40 μ m$ . In the second stage, this combination was used to evaluate the effects of two heat treatment procedures (HT1 and HT2) and two DB processes (using burnishing forces of 100 N and 300 N) on the tensile properties and surface integrity of LPBF 17-4PH SS cylindrical samples. The HT2 procedure, including annealing $(1200^{\circ}$ , $4 h)$ , solution treatment ( $1060^{\circ}$ , $1 h)$ , cooling ( ${- 70}^{\circ} C, 2 h$ ), and ageing ( $482^{\circ}$ , $4 h$ ) led to yield limit, tensile strength, and Vickers hardness values of $Y L = 1071 M P a$ , $T S = 1410 M P a$ , and $523 H V,$ respectively. The concept presented takes advantage of the combination of the transformation, precipitation and strain-hardening effects. The combined effect was most pronounced in the samples subjected to the HT2 procedure and subsequent DB (300 N), for which a retained austenite fraction of 6.93%, surface microhardness of ${563 H V}_{0.05}$ and the maximum values of the compressive axial and hoop RSs of $- 1426.3 M P a$ and $- 1095.9 M P a$ , respectively, were measured.
Open Access
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Cited by 1
- 11 December 2025
- Published by MDPI AG in Applied Sciences
The Effect of Optimised Combined Turning and Diamond Burnishing Processes on the Roughness Parameters of CuZn39Pb3 Alloys
by Kalin Anastasov, Mariana Ichkova, Vladimir Todorov, Petya Daskalova
CuZn39Pb3 leaded brass is one of the most widely used alloys in machining, with a 100% machinability index. However, there has been a lack of research on the effects of coldworking on surface integrity (SI) and operating behaviour of CuZn39Pb3 components. This study addresses this knowledge gap by examining the effects of three optimised combined processes on surface roughness, a key SI characteristic. Specifically, samples were subjected to a turning process followed by diamond burnishing (DB); this combined process was performed under three conditions: conventional flood lubrication (F), dry (D), and dry and cool-assisted (D+C) conditions. Cool-assisted conditions were achieved using a special device with a cold air nozzle operating on the vortex tube principle. The D and D+C conditions represent environmentally sustainable alternatives because they eliminate the use of cutting fluids, thereby reducing their adverse effects on both the environment and human health. The resulting surfaces obtained after each of the three optimised combined processes (F, D, and D+C) exhibited mirror-like finishes with minimum average roughness Ra values of 0.054, 0.079, and 0.082 μm, respectively. In addition, the F- and D+C-processes resulted in surface profiles with negative skewness and kurtosis values greater than three. Since roughness shape parameters are known to influence the operating behaviour of machined components, these processes are suitable for improving wear resistance in boundary lubrication regimes.
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- 11 December 2025
- Published by MDPI AG in Applied Sciences
Open Access
The Effect of Optimised Combined Turning and Diamond Burnishing Processes on the Roughness Parameters of CuZn39Pb3 Alloys
by Kalin Anastasov, Mariana Ichkova, Vladimir Todorov, Petya Daskalova
CuZn39Pb3 leaded brass is one of the most widely used alloys in machining, with a 100% machinability index. However, there has been a lack of research on the effects of coldworking on surface integrity (SI) and operating behaviour of CuZn39Pb3 components. This study addresses this knowledge gap by examining the effects of three optimised combined processes on surface roughness, a key SI characteristic. Specifically, samples were subjected to a turning process followed by diamond burnishing (DB); this combined process was performed under three conditions: conventional flood lubrication (F), dry (D), and dry and cool-assisted (D+C) conditions. Cool-assisted conditions were achieved using a special device with a cold air nozzle operating on the vortex tube principle. The D and D+C conditions represent environmentally sustainable alternatives because they eliminate the use of cutting fluids, thereby reducing their adverse effects on both the environment and human health. The resulting surfaces obtained after each of the three optimised combined processes (F, D, and D+C) exhibited mirror-like finishes with minimum average roughness Ra values of 0.054, 0.079, and 0.082 μm, respectively. In addition, the F- and D+C-processes resulted in surface profiles with negative skewness and kurtosis values greater than three. Since roughness shape parameters are known to influence the operating behaviour of machined components, these processes are suitable for improving wear resistance in boundary lubrication regimes.
Cited by 1
Open Access
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Cited by 1
- 24 November 2025
- Published by MDPI AG in Journal of Manufacturing and Materials Processing
Effects of Electron Beam Hardening Parameters on the Residual Stresses and Microstructures in C45 Steel Cylindrical Specimens
by Galya Duncheva, Vladimir Dunchev, Milka Atanasova, Vladimir Todorov, Yaroslav Argirov, Marieta Ivanova, Boris Petkov
This article presents the effects of novel electron beam hardening (EBH) process parameters in terms of residual stresses (RSs) and microstructure modification in as-received C45 cylindrical specimens. The EBH was performed using continuous irradiation with power in the range of $720 - 2070 W$ on an Evobeam µEBW Cube 400 machine. A distinctive feature of the novel surface hardening process is the linear scanning mode in the axial direction of the treated cylindrical surface, which makes it suitable for machining shafts and axles. Using a one-factor-at-a-time technique, the individual effects of the electron beam current $I_{b}$ , workpiece peripheral velocity $v_{p}$ , scanning frequency (SF), and focal length (FL) on the RSs and microstructure in surface layers were evaluated. The X-ray diffraction results, scanning electron microscopy (SEM) images, and phase analyses confirmed the significant potential of the EBH process for forming compressive RSs due to martensitic transformation in the surface zone and gradient microstructure in terms of structure and phase composition. The measured maximum compressive axial and hoop RSs of $- 289.5$ and $- 345 M P a$ , respectively, and compressive zone at a depth of approximately 0.3 mm correlate with the phase transformation region at a depth of approximately 0.2 mm. Based on the results for RSs and microstructure modification, the limitations with respect to the suitable operating parameter values were established. After excluding these operating parameter values, the following suitable ranges of the operating parameters were determined: $I_{b} \in (16, 36) m A, v_{p} \in (18, 45) m m / s$ , $S F \in (5000, 20,000) H z$ , and $F L \in (+ 5, - 5) m m$ . The specified ranges are the basis for conducting a planned experiment on the novel EBH process.
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- 24 November 2025
- Published by MDPI AG in Journal of Manufacturing and Materials Processing
Open Access
Effects of Electron Beam Hardening Parameters on the Residual Stresses and Microstructures in C45 Steel Cylindrical Specimens
by Galya Duncheva, Vladimir Dunchev, Milka Atanasova, Vladimir Todorov, Yaroslav Argirov, Marieta Ivanova, Boris Petkov
This article presents the effects of novel electron beam hardening (EBH) process parameters in terms of residual stresses (RSs) and microstructure modification in as-received C45 cylindrical specimens. The EBH was performed using continuous irradiation with power in the range of $720 - 2070 W$ on an Evobeam µEBW Cube 400 machine. A distinctive feature of the novel surface hardening process is the linear scanning mode in the axial direction of the treated cylindrical surface, which makes it suitable for machining shafts and axles. Using a one-factor-at-a-time technique, the individual effects of the electron beam current $I_{b}$ , workpiece peripheral velocity $v_{p}$ , scanning frequency (SF), and focal length (FL) on the RSs and microstructure in surface layers were evaluated. The X-ray diffraction results, scanning electron microscopy (SEM) images, and phase analyses confirmed the significant potential of the EBH process for forming compressive RSs due to martensitic transformation in the surface zone and gradient microstructure in terms of structure and phase composition. The measured maximum compressive axial and hoop RSs of $- 289.5$ and $- 345 M P a$ , respectively, and compressive zone at a depth of approximately 0.3 mm correlate with the phase transformation region at a depth of approximately 0.2 mm. Based on the results for RSs and microstructure modification, the limitations with respect to the suitable operating parameter values were established. After excluding these operating parameter values, the following suitable ranges of the operating parameters were determined: $I_{b} \in (16, 36) m A, v_{p} \in (18, 45) m m / s$ , $S F \in (5000, 20,000) H z$ , and $F L \in (+ 5, - 5) m m$ . The specified ranges are the basis for conducting a planned experiment on the novel EBH process.
Cited by 1
Open Access
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- 27 August 2025
- Published by MDPI AG in Engineering Proceedings
Restoration of Working Surfaces for Forming Elements from Molds for High-Pressure Casting of Non-Ferrous Metals by Laser Surfacing
by Vladimir Dunchev, Kalin Anastasov, Vladimir Todorov, Vasil Chobanov, Milka Atanasova
The article presents a study of the possibilities for restoring the working surfaces of molds for high-pressure casting of non-ferrous metals by laser surfacing using a filler material. Test specimens with parameters of real forming elements were manufactured. The influence of nitriding on welded layers and basic material was studied in comparison with one without nitriding. The X-ray diffraction method was used to obtain the phase composition of the surface of the samples in areas submitted to nitriding. Scanning electron microscopy (SEM) was used to determine the microstructure of the nitriding layers, welded layers and bulk material. Energy-dispersive X-ray spectrometry (EDX) was applied to investigate the chemical composition in the welded and nitrided zone. Mechanical property means of microhardness measurements were studied. Four zones were identified after nitriding in the weld area. The first zone closest to the surface with a thickness of 0.025 mm is characterized by a higher microhardness, which reaches 700 HV. The second zone, which is part of the diffusion zone, is 0.1 mm thick, and it is characterized by the same size grains with a similar shape and microhardness, which reaches 600 HV. The microhardness measured in the welded zone after nitriding is 50% greater than that without nitriding. The thickness of the diffusion zone in 1.2343 steel reaches about 0.15 mm, and the microhardness is about 900 HV near the edge, but quickly decreases to 400 HV.
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- 27 August 2025
- Published by MDPI AG in Engineering Proceedings
Open Access
Restoration of Working Surfaces for Forming Elements from Molds for High-Pressure Casting of Non-Ferrous Metals by Laser Surfacing
by Vladimir Dunchev, Kalin Anastasov, Vladimir Todorov, Vasil Chobanov, Milka Atanasova
The article presents a study of the possibilities for restoring the working surfaces of molds for high-pressure casting of non-ferrous metals by laser surfacing using a filler material. Test specimens with parameters of real forming elements were manufactured. The influence of nitriding on welded layers and basic material was studied in comparison with one without nitriding. The X-ray diffraction method was used to obtain the phase composition of the surface of the samples in areas submitted to nitriding. Scanning electron microscopy (SEM) was used to determine the microstructure of the nitriding layers, welded layers and bulk material. Energy-dispersive X-ray spectrometry (EDX) was applied to investigate the chemical composition in the welded and nitrided zone. Mechanical property means of microhardness measurements were studied. Four zones were identified after nitriding in the weld area. The first zone closest to the surface with a thickness of 0.025 mm is characterized by a higher microhardness, which reaches 700 HV. The second zone, which is part of the diffusion zone, is 0.1 mm thick, and it is characterized by the same size grains with a similar shape and microhardness, which reaches 600 HV. The microhardness measured in the welded zone after nitriding is 50% greater than that without nitriding. The thickness of the diffusion zone in 1.2343 steel reaches about 0.15 mm, and the microhardness is about 900 HV near the edge, but quickly decreases to 400 HV.