@inproceedings{PetrovBokuchavaPapushkinetal., author = {Petrov, Peter and Bokuchava, Gizo and Papushkin, Igor and Genchev, Gancho Vladimirov and Doynov, Nikolay and Michailov, Vesselin and Ormanova, Maria}, title = {Neutron diffraction studies of laser welding residual stresses}, series = {19th International Conference and School on Quantum Electronics: Laser Physics and Applications, 26-30 September 2016 Sozopol, Bulgaria}, booktitle = {19th International Conference and School on Quantum Electronics: Laser Physics and Applications, 26-30 September 2016 Sozopol, Bulgaria}, publisher = {SPIE}, address = {Bellingham, Wash.}, isbn = {978-1-5106-0953-2}, doi = {10.1117/12.2261802}, language = {en} } @misc{ValkovKotlarskiOrmanovaetal., author = {Valkov, Stefan and Kotlarski, Georgi and Ormanova, Maria and Doynov, Nikolay and Ossenbrink, Ralf and Petrov, Peter and Michailov, Vesselin}, title = {Crystallography and Mechanical Properties of Wire Arc Additively Manufactured Al5356 Components}, series = {Comptes Rendus de L'Academie Bulgare des Sciences}, volume = {74}, journal = {Comptes Rendus de L'Academie Bulgare des Sciences}, number = {No. 6}, issn = {1310-1331}, doi = {10.7546/CRABS.2021.06.03}, pages = {820 -- 827}, abstract = {In this study, we present results of the evolution of the crystallographic texture and imperfections, as well as the corresponding mechanical properties of wire and arc additively manufactured (WAAM) Al5356 specimens, studied by X-ray diffraction (XRD) and tensile testing, respectively. The results show that the phase composition is in the form of a face-centred cubic (fcc) crystal structure, corresponding to the base material, as well as some traces of oxide phase Al2O3. The WAAM specimen growing is accompanied by a slight change in the preferred crystallographic orientation, from (111) to (200) and a decrease in the imperfections concentration. Also, it was found that the ultimate tensile strength (UTS), yield strength (YS), and elongation slightly decrease from the initial to the more advanced stages of growth.}, language = {en} } @misc{KotlarskiOrmanovaOssenbrinketal., author = {Kotlarski, Georgi and Ormanova, Maria and Ossenbrink, Ralf and Nikitin, Alexander and Doynov, Nikolay and Valkov, Stefan and Michailov, Vesselin}, title = {Fabrication and Characterization of Wire Arc Additively Manufactured AlSi5 Structures}, series = {Metals}, volume = {12}, journal = {Metals}, number = {11}, issn = {2075-4701}, abstract = {For the purpose of this research, single track details were manufactured in the shape of thin walls with a length of 100 mm and a height of 80 mm. Two welding speeds were chosen for this experiment-13.3 mm/s and 20.0 mm/s corresponding to the following heat inputs: 120 J/mm and 80 J/mm. The gas metal arc welding (GMAW) method was used for the build-up of the specimens in the cold arc pulse mode. The structure of the specimens was studied using X-ray diffraction (XRD) analysis carried out with CuKα radiation with a wavelength of 1.5406 Ǻ, optical microscopy, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). Furthermore, the Vickers hardness of the samples was determined using a ZwickRoell DuraScan 10/20 G5 unit at a force of 1 N. A preferred crystallographic orientation towards the (200) plane was observed in all cases, however a vastly textured structure was observed with inclusions of peaks in the (111), (220), and (311) crystallographic planes. The full width at half maximum (FWHM) of samples taken from different stages of build-up was calculated indicating an increase of the dislocation density at the more advanced stages of specimen growth. Despite that an increase of the hardness was observed towards the top of both specimens. This is attributed to the change in the structure of the αAl + Si formations from an irregular one at the bottom of the specimens, towards a fibrous one at the top. The results are discussed in regard to the optimization of the build-up process during wire arc additive manufacturing (WAAM).}, language = {en} } @misc{KotlarskiOrmanovaNikitinetal., author = {Kotlarski, Georgi and Ormanova, Maria and Nikitin, Alexander and Morozova, Iuliia and Ossenbrink, Ralf and Michailov, Vesselin and Doynov, Nikolay and Valkov, Stefan}, title = {Structure Formation and Mechanical Properties of Wire Arc Additively Manufactured Al4043 (AlSi5) Components}, series = {Metals}, volume = {14}, journal = {Metals}, number = {2}, issn = {2075-4701}, doi = {10.3390/met14020183}, abstract = {In the current paper, the correlation between the physical size of additively built wire arc specimens and their structure and properties is studied. For the purpose of this work, two oval shaped specimens of different lengths were manufactured under the same technological conditions. The specimens have a length of 200 mm and 400 mm and will be referred to as L200 and L400. The microstructure of the samples was studied using X-ray diffraction analysis (XRD), optical microscopy, and scanning electron microscopy (SEM). The microhardness, yield strength (YS), and ultimate tensile strength (UTS) were determined and their correlation with the technological conditions of specimen build-up was clarified. The results of the carried out experiments indicated that the crystallographic structure of both specimens is similar. The scanning electron microscopy images show a higher concentration of irregularly shaped micro-pores formed near the edge of the αAl grains in the structure of the L400 specimen compared to the L200 one. An increase in the size of the αAl solid solution grains in the case of the L200 specimen towards its top section was noticed using optical microscopy. A slightly lower magnitude change was noticed concerning the L400 specimen. The increase in the size of the aluminum crystals was determined to be the increasing interpass temperature. Due to the much smaller thermal dissipation capacity of the smaller specimen, the interpass temperature of the same increased faster compared to the larger specimen. All of the above-mentioned factors led to a decrease in the microhardness of the specimens at higher stages of build-up. Since the specimens were deposited using similar layer deposition conditions, the resultant YS and UTS data are also highly comparable.}, language = {en} } @misc{OrmanovaKotlarskiKaishevaetal., author = {Ormanova, Maria and Kotlarski, Georgi and Kaisheva, Darina and Nikitin, Alexander and Ossenbrink, Ralf and Doynov, Nikolay and Valkov, Stefan}, title = {Investigation of the thermal gradients formed during the process of cooling of WAAM built Al99.7 specimen}, series = {Journal of Physics: Conference Series}, volume = {2024}, journal = {Journal of Physics: Conference Series}, number = {2710}, issn = {1742-6596}, doi = {10.1088/1742-6596/2710/1/012038}, abstract = {This work presents a preliminary experiment used to determine the possibility of developing a thermal model used to predict the thermal gradients formed during the process of wire and arc additive manufacturing (WAAM). For this purpose, an Al99.7 specimen was built using gas metal arc welding (GMAW) in the cold arc pulse mode. The temperature of both the substrate and each consecutive layer was measured using thermocouples and infrared thermometers and the experimental data was used for the calibration of the developed thermal model. The obtained results can be used for the further development of the thermal model.}, language = {en} } @misc{KotlarskiOrmanovaNikitinetal., author = {Kotlarski, Georgi and Ormanova, Maria and Nikitin, Alexander and Ossenbrink, Ralf and Doynov, Nikolay and Valkov, Stefan and Michailov, Vesselin}, title = {Structure, morphology and hardness of a WAAM built Al99.7 specimen}, series = {International Scientific Conference Unitech 2023, Gabrovo : selected papers}, volume = {2}, journal = {International Scientific Conference Unitech 2023, Gabrovo : selected papers}, editor = {Tsankov, Plamen and Maximov, Jordan and Aleksandrov, Anatoliy and Todorov, Todor and Peneva, Petya}, publisher = {Union of Automation \& Informatics}, address = {Gabrovo}, issn = {1313-230X}, doi = {10.70456/PJKY7011}, pages = {349 -- 353}, abstract = {The present work discusses the possibility of wire arc additive manufacturing (WAAM) of pure aluminum specimens (Al99.7). The manufactured specimen's structure was studied using X-ray diffraction (XRD) experiments. The morphology of the specimen at different stages of build-up was studied by examining prepared mechanical properties of the specimen, and for this reason the microhardness of the specimen was studied as well. The results of the present study were discussed regarding the change of the structure of the samples with the increase of the specimen's height during the manufacturing process and its influence on the resultant microhardness.}, language = {en} } @misc{KotlarskiOrmanovaNikitinetal., author = {Kotlarski, Georgi and Ormanova, Maria and Nikitin, Alexander and Morozova, Iuliia and Ossenbrink, Ralf and Michailov, Vesselin and Doynov, Nikolay and Valkov, Stefan}, title = {Microstructural and Mechanical Properties of CAP-WAAM Single-Track Al5356 Specimens of Differing Scale}, series = {Materials}, volume = {12}, journal = {Materials}, number = {1}, issn = {2075-1702}, doi = {10.3390/machines12010072}, abstract = {The mass production of metallic components requires high agility in the working process conditioned by the necessity of building details of different shapes and sizes. Changing the size of the components theoretically influences the thermal dissipation capability of the same, which could lead to a change in their structure and mechanical properties. This is particularly important when aluminum alloys are concerned. For this reason, two Al5356 single-track specimens were built using the same technological conditions of layer deposition by varying only their geometrical size. In all cases, the specimens were wire and arc additively manufactured (WAAM) using a process based on gas metal arc welding (GMAW) in the cold arc pulse mode (CAP). The structure of both specimens was studied and defects along their surfaces were detected in the form of micro-pores and micro-cracks. A high concentration of undissolved Mg particles was also detected, along with some standalone Si particles. Uniformity in the build-up process was achieved, which led to the formation of nearly identical structures in the specimens. Subsequently, the resultant mechanical properties were also highly comparable. This indicates that the geometry-related variation in thermal conditions has an insignificant influence on the component's structure and properties.}, language = {en} } @misc{KotlarskiOrmanovaNikitinetal., author = {Kotlarski, Georgi and Ormanova, Maria and Nikitin, Alexander and Parasar, Ashirwad and Ossenbrink, Ralf and Doynov, Nikolay and Valkov, Stefan and Michailov, Vesselin}, title = {Wire arc deposition of specimens using a special-designed aluminum-cored wire with CNTs}, series = {Journal of physics : conference series}, volume = {2994}, journal = {Journal of physics : conference series}, number = {1}, publisher = {IOP Publishing}, address = {Bristol}, issn = {1742-6588}, doi = {10.1088/1742-6596/2994/1/012024}, pages = {1 -- 6}, abstract = {This work investigated the possibility of manufacturing components using an aluminum welding wire with an aluminum powder core reinforced with carbon nanotubes (CNTs). Appropriate technological conditions of deposition were selected for the successful manufacturing of a wall-shaped specimen. The last was built using a multi-track approach. The results indicated the presence of a large quantity of pores within the volume of the specimen with values of over 30\%. Regardless of the high defect quantity within the specimen a number of successfully integrated carbon nanoparticles were detected in certain areas of the cross-section of the specimen in the form of an Al₄C₃ composite.}, language = {en} }