Materials Research and Application II

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Authors: Dragoş Cristian Achiţei, Petrică Vizureanu, Mirabela Georgiana Minciună, Nicanor Cimpoeşu, Bogdan Istrate
Abstract: The paper presents aspects of structure modifications and properties for a CuZn alloy, after the appliance of heat treatments, at their specific parameters. The samples subjected to analysis, coming from cast bar, from which have been taken standard samples, with specific dimensions for experiments.Nonferrous alloys are subject frequently to annealing, quenching and tempering. The annealing follows the homogenization of structure after casting. The quenching followed by tempering is a spectacular modality to modify the mechanical properties for numerous nonferrous alloys.The characteristics of alloys have highlighted by experiments, using standard samples specific to the requests. The determination of alloying elements was made on optical spectrometer. The researches by SEM and optical microscopy, confirm the improvement of properties by obtaining uniform structures according to the applied thermal processing.
Authors: Gabriela Popescu, Mihai Branzei, Cristian Aurelian Popescu, Alecs Andrei Matei, Roxana Trusca, Ioana Csáki
Abstract: During the last years, mechanical alloying technique for high entropy alloys (HEAs) has been more often approached due to the good homogenous chemical distribution and near net shape technology provided by the respectively process. A new composite material having the matrix as HEA reinforced with graphite particles was designed. The graphite particles addition in the high entropy matrix (AlCrFeNiMn) improves the particles weldability during mechanical alloying and assures a good creep behavior for the final product. The aim of this paper is to investigate the pressure influence on the microhardness as dependence of sintering parameters which can be reflected also on the microstructure. The high entropy composite was completely alloyed after 40 hours of milling. The obtained composite was pressed using different pressures values in order to investigate the pressure influence on the microhardness and microstructure. The samples were investigated using optical microscopy, scanning electron microscopy, X-rays diffraction and microhardness tests. The microhardness values for all the samples were between 300 – 700 HV.
Authors: Ioana Csáki, Sigrún Nanna Karlsdottir, Steluța Serghiuță, Gabriela Popescu, Mihai Buzatu, Laura Elena Geambazu, Ciprian Alexandru Manea
Abstract: Mechanical alloying (MA) is a high-energy ball milling process results in the obtaining of simple and stable microstructures having increased homogeneity compared to other non-equilibrium synthesis methods. The aim of this paper was to develop a high entropy alloy with an improved hardness value suitable for coating turbine blades working in geothermal steam. CoCrFeNiMo high entropy alloy was processed in solid state, using mechanical alloying. After 40h milling time in a planetary ball mill the alloyed sample was consolidated using spark plasma sintering process. The samples obtained were investigated with the aid of optical and electron microscope, X ray diffraction and the hardness value was determined. The results obtained revealed that the powder was completely alloyed after 40 hour milling and the mixture between BCC and FCC phases resulted in 34% improved hardness value in comparison with a stainless steel usually used for turbine blades working in geothermal environment.
Authors: Florina Violeta Anghelina, Ionica Ionita, Dan Nicolae Ungureanu, Elena Valentina Stoian, Ileana Nicoleta Popescu, Vasile Bratu, Ivona Petre, Carmen Popa, Alexis Negrea
Abstract: This paper presents experimental results revealed on the samples type 2024 aluminum alloy used in aeronautics. Adequate characterization of 2024 aluminum alloys with special destination (aviation) was achieved by combined investigations:(i) wet chemical analysis, (ii) spectrochemical analysis, (iii) X-ray diffraction and (iv) electron microscopy. The main conclusion that emerges from the investigations carried out on aluminum samples revealed that: (a) alloys fits in terms of composition with the standard specification for 2024, in all cases; (b) microstructure vary in fineness of grain, but meets the requirements of aviation rules; the investigated microstructures have been appreciated as adequate of aluminum alloys type "2024".
Authors: Alaa Abu Harb, Ion Ciuca, Robert Ciocoiu, Mihai Vasile, Adrian Bibis, Bilel Rahali, Ismaiel Al Hawamda
Abstract: The welding technique used for ASIS 304 and 316L austenitic stainless steel sheets both with a thickness of 3mm is gas tungsten arc welding (TIG) and manual metal arc welding (MMAW). Mechanical properties that were verified include: hardness test and tensile test before welding and after it. The welding process was done on two types of specimens: with a central hole and without hole. We concluded that there was a decrease in the properties of tensile for both specimens with central hole, and 316L had tensile characteristics better than 304 when using the technique TIG. As for 304, it had tensile characteristics better than 316L when using the technique MMAW. We also concluded that the existence of central holes had an influence on the hardness characteristics on both types. The hardness increased in 304 but decreased in 316L. The welding process also showed that there was no influence of MMAW on hardness on both specimens. However it showed that there was no influence of TIG on the hardness for 304, but for 316L values increased.
Authors: Gheorghe Buluc, Romeu Chelariu, Gabriela Popescu, Mihail Sârghi, Ioan Carcea
Abstract: Traditional alloys is based on a single element called matrix and to improve some mechanical properties (strength, ductility, strength) are added and other metallic elements in the system. High entropy alloys have become a field of increasingly explored in the world of materials. Excellent mechanical properties obtained of the high entropy alloys recommend them to be from year to year as investigated. In the last decade more than 500 high entropy alloys journal and conference papers have been published [1]. High entropy alloys are alloys who have in their composition 5 to 13 metal elements and the concentration of each component is between 5% and 35%. These elements in the composition of high entropy alloys are divided into elements of minority and majority elements. They are called minority elements because their molar fraction is less than 5%. High entropy alloys have mixing entropy higher than traditional alloys, ΔScons≥1.61R (R = 8.314 J / (mol • K)) [1]. High entropy alloy have been obtained in the laboratory of Science and Materials Engineering faculty from Iasi using a medium frequency induction furnace with 8000 Hz. Because they have excellent mechanical properties high entropy alloys can be used in various fields with high wear and corrosion degree or electronic, magnetic applications [1]. In this work we selected pure metallic elements like: Fe, Ni, Cr, Mn and Al. The quantity of alloy developed varied between 0.5 and 1.5 kg. Metal load necessary for the preparation of metal alloys were formed technical grade, industrial accessible prices and satisfying. Friction and wear rezistance were studies by using a reciprocating sliding test machine , in a pin on disk configuration, using aluminum as counter face.In this paper it investigated the wear resistance of high entropy alloys obtained, microstructure and their mechanical properties.
Authors: Elena Valentina Stoian, Maria Cristiana Enescu, Ivona Petre, Petre Cristian Fluieraru, Alexis Negrea
Abstract: Long steel products type 16CD4 used in car industry must meet high quality conditions regarding chemical composition, surface quality, macro-structural, microstructural and mechanical characteristics. The paper presents the correlations between mechanical characteristics and the main alloying elements of 16CD4 steel; this will give varying characteristics Rm, A5 and KCU, in correlation with the various proportions of chrome, molybdenum and carbon contained by steel. This steel brand is part of the chosen alloy steels, presenting plastic deformation resistance in conditions of high temperature. See that it is not necessary maximum carbon content for the mechanical characteristics have maximum values. The material studied was 16CD4 steel (17MoCr11), developed in EBT and treated steel to LF. Mechanical properties dependent of the content of carbon, chromium and molybdenum have been analyzed in this paper, using a mathematical model. Model verification was conducted by test Fischer and the results indicate that there are strong correlations between the mechanical properties and the percentage of carbon, chromium and molybdenum.
Authors: Sveto Cvetkovski
Abstract: The heat input during conventional arc welding processes can be readily calculated knowing the power taken from the power source. The efficiency coefficient can be taken from the appropriate literature standards. Here, the intention of the performed research work was to develop a procedure for determination of heat input in arc and laser welding processes implementing Adams equation - modified Rykalin equation for two dimensional heat distributions (2-D). To realize this idea, it is necessary to determine two characteristic temperatures points in the HAZ with known peak temperature, and to determine distance between them. Implementing measured values for distance in Adams’ equation, heat input in arc welding can be directly determined in arc welded joints.In laser beam welding, the absorption of the beam in the metal is not known, so that the welding heat input cannot be calculated directly, and direct implementation of Adam’s equation is not possible i.e. absorption coefficient has to be determined first, and after that calculation of heat input is possible.The peak temperatures corresponding to specific microstructures can be obtained by performing welding simulation, by the Gleeble 1500 simulator in our case. As one of the peak temperatures, the melting temperature can be used corresponding to the fusion line, so that at least one characteristic peak temperature such as coarse grain zone, fine grin zone, intercritical zone, recrystallization, has to be determined by the simulation.Performed research showed that obtained values for heat input using Adam’s equation correspond pretty well with standard equation for heat input in arc welding.
Authors: Fabrizio Fiori, Emmanuelle Girardin, Alessandra Giuliani, Adrian Manescu, Serena Mazzoni, Franco Rustichelli, Evzen Amler
Abstract: The rapid development of new materials and their application in an extremely wide variety of research and technological fields has lead to the request of increasingly sophisticated characterization methods. In particular residual stress measurements by neutron diffraction, small angle scattering of X-rays and neutrons, as well as 3D imaging techniques with spatial resolution at the micron or even sub-micron scale, like micro-and nano-computerized tomography, have gained a great relevance in recent years.Residual stresses are autobalancing stresses existing in a free body not submitted to any external surface force. Several manufacturing processes, as well as thermal and mechanical treatments, leave residual stresses within the components. Bragg diffraction of X-rays and neutrons can be used to determine residual elastic strains (and then residual stresses by knowing the material elastic constants) in a non-destructive way. Small Angle Scattering of neutrons or X-rays, complementary to Transmission Electron Microscopy, allows the determination of structural features such as volume fraction, specific surface and size distribution of inhomogeneities embedded in a matrix, in a huge variety of materials of industrial interest. X-ray microtomography is similar to conventional Computed Tomography employed in Medicine, allowing 3D imaging of the investigated samples, but with a much higher spatial resolution, down to the sub-micron scale. Some examples of applications of the experimental techniques mentioned above are described and discussed.

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