Galya Velikova Duncheva

Prof. Galya Velikova Duncheva

Material Science and Mechanics of Materials, Technical University of Gabrovo, 5300 Gabrovo, Bulgaria
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Research Focus & Metrics

Academic Career Length

7Years (2020-Present)

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

Representative Publications

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7 July 2022 in Materials
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Journal Article
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Jordan MaximovJordan Maximov
Jordan Maximov
Galya Velikova DunchevaGalya Velikova Duncheva
Galya Velikova Duncheva
Angel Petrov AnchevAngel Petrov Anchev
Angel Petrov Anchev
VDVladimir Petrov Dunchev
Vladimir Petrov Dunchev
YAYaroslav Borisov Argirov
Yaroslav Borisov Argirov
The disadvantages of widely used austenitic stainless steels are their low hardness and relatively low fatigue strength. Conventional chemical-thermal surface treatments are unsuitable for these steels since they create conditions for inter-granular corrosion. An effective alternative is a low-temperature surface treatment, creating an S-phase within the surface layer, but it has a high cost/quality ratio. Austenitic steels can increase their surface micro-hardness and fatigue strength via surface cold working. When the goal is to increase the rotating bending fatigue strength of austenitic chromium-nickel steels, and the requirements for significant wear resistance are not paramount, diamond burnishing (DB) has significant potential to increase the fatigue strength and, based on the cost/quality ratio, can successfully compete with low-temperature chemical-thermal treatments. The main objective of this study is to establish the effect of DB on the rotating fatigue strength of AISI 304 L chromium-nickel austenitic steel. The influence of DB parameters on the surface integrity (SI) characteristics was studied. Optimal DB parameters under minimum roughness and maximum micro-hardness criteria were obtained. Rotating bending fatigue tests of the diamond burnished (in a different manner) and untreated specimens were performed. DB implemented via parameters providing maximum micro-hardness increased fatigue limit by 38% compared to untreated specimens.

16 February 2023 in Applied Sciences
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Journal Article
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Jordan MaximovJordan Maximov
Jordan Maximov
Galya Velikova DunchevaGalya Velikova Duncheva
Galya Velikova Duncheva
Angel Petrov AnchevAngel Petrov Anchev
Angel Petrov Anchev
VDVladimir Petrov Dunchev
Vladimir Petrov Dunchev
YAYaroslav Borisov Argirov
Yaroslav Borisov Argirov
Maria NikolovaMaria Nikolova
Maria Nikolova
The surface cold working (SCW) of austenitic stainless steel (SS) causes martensitic transformation in the surface layers, and the percentage fraction of the strain-induced martensite depends on the degree of SCW. Higher content of α′−martensite increases the surface micro-hardness and fatigue strength, but deterioration of the corrosion resistance is possible. Therefore, the desired operational behaviour of austenitic SS can be ensured by the corresponding degree of SCW and heat treatment. This article evaluates the effects of SCW performed by diamond burnishing (DB) and heat treatment on the surface integrity (SI), rotating fatigue strength, and corrosion resistance of AISI 304 austenitic SS for two initial states: as-received hot-rolled bar and initially heat-treated at 1100 °C for one hour followed by quenching in water. Then, DB was implemented as a smoothing and hardening process, both alone and in combination with heat treatment at 350 °C for three hours after DB. The electrochemical performance was examined by open circuit potential measurements, followed by potentiodynamic tests. For both initial states, smoothing DB provided the lowest roughness, whereas an improvement in the maximum surface micro-hardness was obtained after hardening DB and subsequent heat treatment. The maximum fatigue strength was obtained by hardening multi-pass DB without subsequent heat treatment for the as-received initial state. Smoothing DB and subsequent heat treatment maximised the surface corrosion resistance for the two initial states, whereas a minimum corrosion rate was obtained for the initially heat-treated state. For the as-received state, smoothing DB and subsequent heat treatment simultaneously lead to a high fatigue limit (equal to that obtained by hardening single-pass DB) and a low corrosion rate.

13 September 2022 in Wear
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Journal Article
Closed access
Galya Velikova DunchevaGalya Velikova Duncheva
Galya Velikova Duncheva
JMJ.T. Maximov
J.T. Maximov
AAA.P. Anchev
A.P. Anchev
VDV.P. Dunchev
V.P. Dunchev
YAY.B. Argirov
Y.B. Argirov
MKM. Kandeva-Ivanova
M. Kandeva-Ivanova

5 March 2023 in Applied Sciences
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Journal Article
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Jordan MaximovJordan Maximov
Jordan Maximov
Galya Velikova DunchevaGalya Velikova Duncheva
Galya Velikova Duncheva
This review paper analyses and summarises the results found while studying the slide burnishing (SB) of metal components refracted through a prism during the surface engineering (SE) process, over the period of January 2019 to January 2023. According to the classification of SE processes defined in the article, SB as a technique in the scope of SE that belongs to the group of static surface cold working (SCW) processes, based on severe surface plastic deformation, and is realised under the condition of sliding friction contact with the treated surface. When the deforming element is natural or artificial diamond, SB is known as diamond burnishing (DB). SB is especially suited for axes, shafts, and holes with circular cross-sections but can also be implemented on flat-face and complex surfaces. SB is eco-friendly and a very economical method for producing mirror-like surface finishes on a wide range of ferrous and non-ferrous machined surfaces, but it can also be realised as a hardening and mixed process with the aim of significantly increasing the fatigue strength and wear resistance of the treated components. Based on a literature review of the results of the theory and practice of SB, an analysis on different criteria was carried out, and graphic visualizations of the statistical results were made. Additionally, the results were analysed using the integrated approach of SE to study the correlations between the apexes of the triangle: SB—surface integrity (SI)—operational behaviour (OB). On this basis, relevant conclusions were drawn, and promising directions for future investigations of SB were outlined.

13 November 2020 in The International Journal of Advanced Manufacturing Technology
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Journal Article
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Galya Velikova DunchevaGalya Velikova Duncheva
Galya Velikova Duncheva
JMJ. T. Maximov
J. T. Maximov
VDV. P. Dunchev
V. P. Dunchev
AAA. P. Anchev
A. P. Anchev
TAT. P. Atanasov
T. P. Atanasov
JCJiri Capek
Jiri Capek

11 January 2024 in Machines
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Journal Article
Open access
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Jordan MaximovJordan Maximov
Jordan Maximov
Galya Velikova DunchevaGalya Velikova Duncheva
Galya Velikova Duncheva
Angel Petrov AnchevAngel Petrov Anchev
Angel Petrov Anchev
VDVladimir Petrov Dunchev
Vladimir Petrov Dunchev
KAKalin Anastasov
Kalin Anastasov
Petya DaskalovaPetya Daskalova
Petya Daskalova
The article presents a new method called slide roller burnishing (SRB) for the cold working of cylindrical surfaces on machine tools implemented with a novel multi-functional device. The machined material is chromium–nickel austenitic stainless steel. The deforming element is a toroidal roller whose axis crosses that of the workpiece. As a result, a relative sliding velocity occurs in the contact zone between the roller and the machined surface. The sliding velocity vector is set using the burnishing device. The theoretical background of SRB is presented. When the two axes are parallel, the well-known roller burnishing (RB) method is implemented. Thus, RB is a special case of SRB. Both processes are realized using the multi-functional burnishing device. The RB process was studied experimentally and optimized according to three criteria, based on the relationship between the surface integrity and operating behavior of the respective component, to achieve three processes: smoothing, hardening, and mixed burnishing. Using the optimal RB parameters obtained, the dependence of the results of SRB on the crossing angle was investigated and optimized. A comparative analysis was performed between the optimized RB and SRB processes (respectively for their three variants: smoothing, hardening, and mixed) based on geometrical and physical–mechanical characteristics of the surface integrity. The main advantage of the SRB is that it provides smaller height roughness parameters (improvement by 42%) and a higher surface microhardness (improvement by 7%) than RB.