Papers by Ionelia Voiculescu
International Multidisciplinary Scientific GeoConference SGEM ..., Dec 15, 2023
Materials, Mar 1, 2024
The structure, composition and corrosion properties of thin films synthesized using the Pulsed La... more The structure, composition and corrosion properties of thin films synthesized using the Pulsed Laser Deposition (PLD) technique starting from a three high entropy alloy (HEA) AlCoCrFeNix produced by vacuum arc remelting (VAR) method were investigated. The depositions were performed at room temperature on Si and mirror-like polished Ti substrates either under residual vacuum (low 10 -7 mbar, films denoted HEA2, HEA6, and HEA10, which were grown from targets with Ni concentration molar ratio, x, equal to 0.4, 1.2, and 2.0, respectively) or under N 2 (10 -4 mbar, films denoted HEN2, HEN6, and HEN10 for the same Ni concentration molar ratios). The deposited films' structures, investigated using Grazing Incidence X-ray Diffraction, showed the presence of face-centered cubic and body-centered cubic phases, while their surface morphology, investigated using scanning electron microscopy, exhibited a smooth surface with micrometer size droplets. The mass density and thickness were obtained from simulations of acquired X-ray reflectivity curves. The films' elemental composition, estimated using the energy dispersion X-ray spectroscopy, was quite close to that of the targets used. X-ray Photoelectron Spectroscopy investigation showed that films deposited under a N 2 atmosphere contained several percentages of N atoms in metallic nitride compounds. The electrochemical behavior of films under simulated body fluid (SBF) conditions was investigated by Open Circuit Potential (OCP) and Electrochemical Impedance Spectroscopy measurements. The measured OCP values increased over time, implying that a passive layer was formed on the surface of the films. It was observed that all films started to passivate in SBF solution, with the HEN6 film exhibiting the highest increase. The highest repassivation potential was exhibited by the same film, implying that it had the highest stability range of all analyzed films. Impedance measurements indicated high corrosion resistance values for HEA2, HEA6, and HEN6 samples. Much lower resistances were found for HEN10 and HEN2. Overall, HEN6 films exhibited the best corrosion behavior among the investigated films. It was noticed that for 24 h of immersion in SBF solution, this film was also a physical barrier to the corrosion process, not only a chemical one.
19th International Scientific Conference on Industrial Systems
The Mg-Zn alloys have a controlled biodegradability in biological fluids. Alloys in the Mg-Zn sys... more The Mg-Zn alloys have a controlled biodegradability in biological fluids. Alloys in the Mg-Zn system must be manufactured from high-purity raw materials, and the production process must be free of impurities from the crucibles. The mechanical properties of Mg-Zn alloys can reach values of tensile strength of 270 MPa and elongation at break of over 18%. The use of these alloys for bio-resorbable implantable devices does not allow the existence of a high level of impurities. For this reason, in the work has been used an installation for melting raw materials by levitation, which allows the metal alloy to be kept in an inert gas environment inside an induction coil, avoiding its contact with any other material. The induction currents generated in the levitational floating melt determine the mixing of the chemical elements and the homogenization of the alloy. In this paper, seven experimental Mg-Zn-Y alloys with different chemical compositions were produced and tested. To reduce the oxi...
Materials Today: Proceedings, 2023
Materiale Plastice, Jun 30, 2018
The paper describes the advantages of material deposition using the resistive vaporization method... more The paper describes the advantages of material deposition using the resistive vaporization method, so that new very thin layer, which is about ìm, could be used on polymer base structure. Due to the new properties involving the friction coefficient on plane surface, where some dynamic forces are acting, we may better control the performances. By analyzing the theoretical aspects of entropy rate production, we may determine the maximum friction providing the stability of wear avoiding the material deterioration during the process.
Microscopy and Microanalysis, Jul 30, 2021
IOP conference series, Jun 1, 2018
View the article online for updates and enhancements. Content from this work may be used under th... more View the article online for updates and enhancements. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Applied Mechanics and Materials, Oct 1, 2014
The paper presents research made to achieve environmental powder precursors from a CuSnP alloy, u... more The paper presents research made to achieve environmental powder precursors from a CuSnP alloy, used in the manufacturing process of brazing materials, such as coated rods. The innovation of the paper consists in the elemental participation of the components in the new alloys, procedure that takes place in the alloying process, through coat conditions of the addition materials and by simultaneous obtaining the new precursors that fulfill high friability and deoxidation conditions of the participants in the brazing process. Developing the copper alloy batches is conditioned by a good protection to oxidation and gas absorption from the melting oven atmosphere. In order to protect the melt from the above mentioned phenomena’s we developed a slagging flux, boron-cryolithe type, which has melting proprieties below those of the copper phosphorus alloy, approx. 700°C. The load calculation was made based on the technical characteristics of the industrial base materials that were used, taking into account the loss coefficient of 5%. The melting, casting and cooling of the samples, dimensioned so they will be friable, was accomplished through classic procedures. The grinding of the sample, including the moistening thermic treatments, was achieved by experimental research, followed by calculations, based on the criteria of maximum yield for grinding. Estimating the sample friability, in the preliminary phase of the experimental determinations, was needed in order to restrain the testing domain, through structural and hardness analyses. The chemical composition of the samples was spectral determined on the copper and copper phosphorus programs.
IOP conference series, Jun 1, 2016
Due to their special properties at high temperatures, FeCrAl alloys micro-alloyed with Zr can be ... more Due to their special properties at high temperatures, FeCrAl alloys micro-alloyed with Zr can be regarded as potential materials for use at nuclear power plants, generation 4R. These materials are resistant to oxidation at high temperatures, to corrosion, erosion and to the penetrating radiations in liquid metal environments. Also, these are able to form continuously, by the self-generation process of an oxide coating with high adhesive strength. The protective oxide layers must be textured and regenerable, with a good mechanical strength, so that crack and peeling can not appear. To improve the mechanical and chemical characteristics of the oxide layer, we introduced limited quantities of Zr, Ti, Y, Hf, Ce in the range of 1-3%wt in the FeCrAl alloy. These elements, with very high affinity to the oxygen, are capable to stabilize the alumina structure and to improve the oxide adherence to the metallic substrate. FeCrAl alloys microalloyed with Hf were prepared using VAR (Vacuum Arc Remelting) unit, under high argon purity atmosphere. Three different experimental alloys have been prepared using the same metallic matrix of Fe-14Cr-5Al, by adding of 0.5%wt Hf, 1.0%wt Hf and respectively 1.5%wt Hf. The microhardness values for the experimental alloys have been in the range 154 ... 157 HV0.2. EDAX analyses have been performed to determine chemical composition on the oxide layer and in the bulk of sample and SEM analyze has been done to determine the microstructural features. The results have shown the capacity of FeCrAl alloy to form oxide layers, with different texture and rich in elements such as Al and Hf.
Wiley-VCH Verlag GmbH & Co. KGaA eBooks, Feb 3, 2011
Key Engineering Materials, Sep 1, 2013
Stainless steels, commercial as well as with special properties, are the principal metallic mater... more Stainless steels, commercial as well as with special properties, are the principal metallic materials used for medical devices manufacturing. Stainless steels for medical devices should have superior mechanical properties, as: hardness, wear resistance, tensile strength, elongation, fracture toughness, creep resistance etc. This paper aims to present experimental researches regarding the obtaining in vacuum arc remelting device (VAR) of austenitic and martensitic stainless steels and their characterization from microstructure and microhardness point of view.
International Journal of Engineering Research in Africa, Aug 1, 2018
Many high entropy alloy systems have been exploited in the past decade and among them AlCrFeCoNi ... more Many high entropy alloy systems have been exploited in the past decade and among them AlCrFeCoNi alloy is widely studied. The structural and mechanical properties of AlCrxFeCoNi alloy was studied in this paper for different content of chromium (atomic ratio, x= 0.2 to 2.0 at. %). In this study, ten samples having different chemical composition were prepared from raw materials using RAV equipment, type MRF ABJ 900. The microstructure features, crystallite sizes and microhardness depends on chemical composition of the alloy. The microhardness values for AlCrxFeCoNi (x = 0.2 to 2 at. %) increases from 389.6 to 562.6 HV0.1. The maximum value of microhardness for the high entropy alloy AlCrxFeCoNi (x = 1), has been obtained for 20.55 wt% Cr and has the value 562.6 HV0.1.
Materials and Manufacturing Processes, May 9, 2016
This paper presents an alternative approach to obtaining crack- and pore-free NiCrBSiFeCuMoC hard... more This paper presents an alternative approach to obtaining crack- and pore-free NiCrBSiFeCuMoC hard coatings on a low alloy steel substrate through coaxial laser cladding, by using Inconel 718 as a buffer layer between the hard coating and the base material. The presence of the buffer layer reduces the overall cracking susceptibility of the hardfacing material by reducing the compressive stresses developed during the cladding process and ensuring a more uniform heat distribution gradient at the surface of the material than the base metal alone, which provides an additional hardness and wear coefficient increase of 7% and improves the corrosion resistance of the obtained materials by 20%, in comparison with the reference sample obtained without an intermediate layer, by using the same operational parameters and minimizes elemental dilution with the substrate. Our method could prove useful in increasing the quality and life cycle of expensive high-performance hard-coated materials, especially those working under demanding operational and environmental conditions.
Microscopy and Microanalysis, Jul 22, 2023
Metals, Jun 7, 2021
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
IntechOpen eBooks, Jun 24, 2020
High-entropy alloys (HEAs) can be obtained using various metallurgical processes such as vacuum a... more High-entropy alloys (HEAs) can be obtained using various metallurgical processes such as vacuum arc remelting (VAR), induction melting, powder metallurgy, additive manufacturing, plasma sintering of powders, etc. Among these methods, the obtaining process in the VAR plant provides superior homogeneity characteristics for metal matrices, simultaneously with advanced purity, due to the high level of protection of the melts. The chapter presents a series of results on alloys with high entropy from the AlCrFeCoNi system, which can be used for various applications, including in the military field, for the realization of high-speed penetration protection panels. Experimental alloys were obtained by melting in electric arc under an argon atmosphere, using high-purity raw materials (greater than 99.5 wt%), and homogenization is ensured by successive five-times remelting of mini-ingots. The obtained alloys were subjected to microstructural analyses, mechanical tests, and also dynamic impact tests using incendiary perforation projectiles. At the same time, some tests were carried out on ballistic packages made of different materials, including high-entropy alloys. The results obtained in mechanical tests revealed high values of microhardness (over 600 HV 0.1) as well as compressive strengths above 2000 MPa. The mechanical characteristics of these alloys can undergo substantial changes by applying several heat treatments.
Microscopy and Microanalysis, Jul 22, 2023
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Papers by Ionelia Voiculescu
materials used for medical devices manufacturing. Stainless steels for medical devices should have
superior mechanical properties, as: hardness, wear resistance, tensile strength, elongation, fracture
toughness, creep resistance etc. This paper aims to present experimental researches regarding the
obtaining in vacuum arc remelting device (VAR) of austenitic and martensitic stainless steels and
their characterization from microstructure and microhardness point of view.
harbour, Israel, in 1966, next to the Tower of Flies, after which
it was named. The shipwreck was excavated in 2012 and
2013. During the underwater excavations, two metal concretions
were retrieved, X-rayed, and on opening were found to
contain three almost identical iron-bound deadeyes. An iron
bolt was also retrieved, covered with concretion. Metallurgical
characterization was used to elucidate the manufacturing technology
and to date the items. The artefacts were found to be
made of annealed wrought iron. The use of wrought
iron, forge-welding, and the presence of 0.1–0.2 wt.%
Mn may indicate manufacturing in the mid-nineteenth
century. Combined with the transition from hemp to
chain cable for rigging in 1808, and by the 1840s to
wire rope, all the indications are that the deadeyes were
made in the second quarter of the nineteenth century.
The size of the deadeyes, and the dimensions of their
chain links, may indicate their use at the topmast of a
brig of about 160 T. This agrees with other evidence in
suggesting that the Akko Tower Wreck is the remains
of a European vessel which sank in Akko harbour about
the second quarter of the nineteenth century.