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4 results on '"R.V. Gădălean"'

1. Consolidation and Characterisation of Hard Metal Powders Milled under Dichloromethane

Author

H.-F. Chicinaș, O.-D. Jucan, R.V. Gădălean, G. Conțiu, A. Cotai, and C.O. Popa

Subjects
hard metal, sintering, milling, particle, dichloromethane, Mining engineering. Metallurgy, TN1-997, Materials of engineering and construction. Mechanics of materials, TA401-492
Abstract

This work presents the development of a safer processing route for hard metals. Traditional processing of fine particles under organic solvents presents significant explosion risks. The milling under dichloromethane (DCM) reduces the risks associated with fire hazards. After milling and drying, the samples have been sintered in an industrial sintering furnace under a vacuum at 1380°C. The materials’ characterisation has been done by X-ray diffraction, scanning electron microscopy, particle size analysis, optical microscopy, and by magnetic measurements. The present work results reveal the powders’ appropriate properties after milling and drying and the desired biphasic (Co-WC) phases obtained after sintering, thus proving the feasibility of such a route, therefore the diminishing of specific fire hazards.

Published
2022
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2. Additive Manufacturing of WC-Co by Indirect Selective Laser Sintering (SLS) using High Bulk Density Powders

Author

R.V. Gădălean, O.-D. Jucan, H.F. Chicinaş, N. Bâlc, and C.O. Popa

Subjects
additive manufacturing, selective laser sintering, cemented carbide, polyamide 12, Mining engineering. Metallurgy, TN1-997, Materials of engineering and construction. Mechanics of materials, TA401-492
Abstract

Research in additive manufacturing of tungsten carbide-cobalt has intensified over the last few years due to the increasing need for products designed using topology optimisation and multiscale structures (lattice). These products result in complex shapes and contain inner structures that are challenging to produce through conventional techniques, thus involving high costs. The present work addresses this problem using a two-step approach to 3D print parts with complex shapes and internal structures by employing indirect selective laser sintering (SLS) and tungsten carbide-cobalt sintering. The paper takes further our research in this field [1] to improve the part density by using high bulk density tungsten carbide-cobalt powders. Mechanically mixing tungsten carbide-cobalt with the sacrificial binder, polyamide 12, results in a homogenous powder successfully used by the selective laser sintering process to produce green parts. By further processing, the green parts through a complete sintering cycle, an average final part density of 11.72 g/cm3 representing more than 80% of the theoretical density is achieved.

Published
2022
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3. Study on the indirect selective laser sintering (SLS) of WC-Co/PA12 powders for the manufacturing of cemented carbide parts

Author

M. Hering, Catalin Popa, H.F. Chicinaş, N. Bâlc, R.V. Gădălean, and O.D. Jucan

Subjects
Materials science, 020502 materials, Metallurgy, Sintering, 3d model, 02 engineering and technology, General Medicine, law.invention, Selective laser sintering, 0205 materials engineering, Volume (thermodynamics), law, Polyamide, End mill, Cemented carbide, Shrinkage
Abstract

A new approach for the manufacturing of cemented carbide parts with a high degree of complexity via indirect selective laser sintering (SLS), using commercial WC-12Co with different amounts of polyamide (PA12) and using low-cost standard equipment is proposed. After debinding, vacuum sintering and sinter-HIP at 1400 °C with 50 bar Ar of the green specimens, the samples showed low relative densities in the range of 60–66%, while the shrinkage after sintering ranged between 35% and 42%, being constant within the volume. This method enables the production of complex shape parts which retained their shape even with respect to the cooling channels after sintering, showing good surface quality and geometry definition. The 3D scan of a WC-12Co end mill sample with 20% PA12 showed low dimensional deviation compared to the 3D model (.stl), proving the capability of the SLS to manufacture near-net-shape cemented carbide parts. The obtained results are indicating that, by adopting a better suited WC-Co powder, indirect SLS followed by Sinter-HIP, can become an interesting method for the Additive Manufacturing of complex cemented carbide parts.

Published
2021
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4. Influence of milling media on the properties of some hard metal powders

Author

H.F. Chicinaş, R.V. Gădălean, G. Conțiu, Traian Florin Marinca, D. O. Jucan, A. Eckert, P. Götze, and Catalin Popa

Subjects
chemistry.chemical_compound, Aqueous solution, Materials science, Hard metal, Chemical engineering, chemistry, Aqueous medium, Agglomerate, Economies of agglomeration, Acetone, General Medicine
Abstract

This paper presents the results of using an aqueous milling media in comparison with traditional milling routes, as well as the influence of the milling media interaction with powder on the morphology and agglomeration behaviour. Hard Metal powders were milled in four milling media, two of them consisting of traditional milling routes and two of them aqueous routes. The aqueous milled powder is larger in size, similar to acetone and exhibits higher hardness as compared to the powder milled using isohexane, acetone, thus lowering the pressability. The pH adjustment of the water leads to soft agglomerates similar to isohexane and acetone. Powder oxidation occurs after the drying process, being more intense in the case of using an aqueous medium. Using N2 atmosphere has inhibited the powder oxidation for the powder milled in traditional media. Using CO2 or by gradual exposure to air the spontaneous oxidation is prevented for aqueous processing.

Published
2021
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