Navegação Periódicos - Resumos por ID Autor IPEN "982"

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  • IPEN-DOC 27025

    FONSECA, DANIELA P.M. da ; MONTEIRO, WALDEMAR A. . Analysis by optical microscopy and x-ray diffraction of composite Cu-Cr-Ag-Al2O3 synthesized using powder metallurgy. Acta Microscópica, v. 26, Supplement B, p. 278-279, 2017.

    Abstract: The use of Nature's materials in favor of human beings has been present in its daily life for a long time, copper and its alloys have been used in function of the high thermal and electrical conductivity, good mechanical properties, resistance to corrosion, ease of fabrication and also by the high value of scrap [1]. Metal alloys can also be combined with other classes of materials in order to obtain new properties, superior to the original alloy, this union of two or more materials forms a composite [2]. The studied composite has a ternary metal alloy (copper, chromium and silver) as a matrix and a ceramic oxide (alumina) as the reinforcing phase. The addition of chromium, silver and small amounts of finely dispersed metal oxides in copper improves their mechanical properties and increases the operating temperature, causing little loss of conductivity. A possible application of this composite is in electrical contacts, electronic devices that break the passage of current in electrical circuits [1]. The objective of this study was the microstructural characterization by optical microscopy and X-ray diffraction of the composite Cu-Cr-Ag-Al2O3 processed by powder metallurgy. The samples used were fabricated in laboratory scale of 25 mm diameter, 3,5 mm  ℎ  4,0 mm of height and 6,5 g of mass, with the following chemical compositions: (a) 85% Cu – 15% Al2O3; (b) 90% Cu – 5% Cr – 2% Ag – 3% Al2O3; (c) 90% Cu – 5% Cr – 5% Al2O3; (d) 90% Cu – 7% Cr – 3% Al2O3; (e) 85% Cu – 5% Cr – 5% Ag – 5% Al2O3; (f) 90% Cu – 5% Cr – 3% Ag – 2% Al2O3; (g) 90% Cu – 3% Cr – 7% Al2O3. In order to obtain the samples, the powders were weighed on a precision balance (according to each composition), mixed manually and cold-compacted in uniaxial press with 450 MPa pressure and sintered in an EDG furnace under 10-3 torr of mechanical vacuum and 650 °C in 6 h. The samples were prepared metallographically and observed in an optical microscope, the micrographs indicated coalescing of the copper particles and other metallic elements and formation of porosity (figure 1). The X-ray diffraction data were collected for samples (a) and (e) using graphite monochromator, copper tube, 25º ≤ 2θ ≥ 90º and Δ2θ = 0,02, from the diffractograms the mean crystallite size (𝐷) and microdeformation (𝜖) were calculated using the Williamson-Hall graphical method where the approximate line has a linear coefficient equal to 1/𝐷 and the angular coefficient is equal to 4𝜖/𝜆 [3]. In both samples were identified the expected phases, in agreement with the composition, and an undesirable phase of copper oxide (figure 2). The Williamson-Hall method was not used for all phases because it requires the identification of at least three peaks. Optical micrographs indicated presence of porosity inside the structure and partial homogeneity, due to the non-dissolution of the elements involved in the metal alloy, it is necessary to do further special thermal treatments. In some samples, a third phase was recognized, whose composition demands microanalyses to be properly identified. Through the diffractograms it was possible to identify the phase of copper oxide possibly coming from the sintering stage, this phase is not desirable or this composite because it negatively influences its electrical and mechanical properties. The Williamson-Hall method obtained a straight line with good correlation and suitable values of mean crystallite size and microdeformation for the copper phase.

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  • IPEN-DOC 24944

    FONSECA, DANIELA P.M. da; MONTEIRO, WALDEMAR A. . Microstructural analysis of composite Cu-Cr-Ag-(CeO2, Al2O3) processing by powder metallurgy. Acta Microscópica, v. 26, B, p. 280-281, 2017.

    Abstract: Copper has long been used by mankind, since the 20th century they have gained industrial and technological importance [1]. They can be combined with ceramic materials in the synthesis of modern composites, optimized and with balanced properties [2]. The studied composite has a metal as a matrix (copper or copper, chromium and silver), the ceramic oxide as the reinforcing phase (ceria or alumina) and was synthesized by powder metallurgy. A possible application of this material is like anodes in Solid Oxide Fuel Cells (SOFC), cermets based on rare earth oxides and metals such as copper, silver and nickel have been studied in this component [3]. The objective of this work was the analysis of the particle size by SEM and chemical composition by EDS of the starting material (powders of copper, chromium, silver, ceria and alumina) and the microstructural characterization by MO of copper composites with four compositions: (a) 80% Cu – 8% Cr – 4% Ag – 8% CeO2; (b) 80% Cu – 20% CeO2; (c) 80% Cu – 8% Cr – 4% Ag – 8% Al2O3; (d) 80% Cu – 20% Al2O3. For analysis in the SEM/EDS the powders were fixed in the sample port with carbon paint, for the powders of ceria and alumina was made gold coating for 2 min. The copper powder presented nodular agglomerates; the chromium powder presented large particles with coarse contours and irregular shape; the silver powder presented a dendritic shape; the ceria powder presented very small particles and it was not possible to observe them due to the limitation of the SEM and the alumina powder presented flake-shaped agglomerates, figure 1. The EDS microanalysis results for copper, silver, ceria and alumina powders were adequate, for chromium powder indicated silicon and iron (manufacturer predicted) and calcium impurities (not predicted but with low percentage), figure 1. The powders were weighed on a precision balance (according to each composition), mixed manually and cold-compacted in uniaxial press with 180 MPa pressure and sintered in a tubular furnace with vacuum of 10-7 torr, temperature of 750 °C and time of 6 h. The samples were obtained in laboratory scale with a 31x12x 3.5 mm parallelepipedal shape, hot mounting, grinded (240, 320, 400, 600, 800) and polished (3μm and 1μm diamond and 0.02 μm silica). The optical micrographs indicated coalescence of copper particles, homogeneity, porosity and an unknown (black) phase, possibly related to ceramic materials, figure 2. The sample (c) was the only one that presented different microstructure between the normal and transverse directions, possibly due to segregation of the powders during mixing. It was possible to make an adequate analysis of the particle formats of the copper, chromium, silver and alumina powders; however, the ceria powder needs to be analyzed again in SEM with higher capacity of increase. The results of EDS microanalysis were promising for all powders. The optical micrographs suggest a good adequacy of the compaction and sintering parameters, forming a homogeneous microstructure and with the desired porosity, except for sample (c), that the mixture was not suitable. In order to study the formed phases it is necessary to perform an X-ray mapping on SEM and X-ray diffraction in the samples after sintering.

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  • IPEN-DOC 27024

    DIAS, RENAN A.F. ; MONTEIRO, WALDEMAR A. . Microstrutural evolution of nickel-based superalloy processed by Equal-Channel Angular Pressing (ECAP). Acta Microscópica, v. 26, Supplement B, p. 71-72, 2017.

    Abstract: The present work shows the microstructural (under optical microscopy) and Vickers hardness evolution of a nickel-based superalloy Inconel 600 (alloy 600) before and after deformed by Equal-Channel Angular Pressing (ECAP) that significantly modified the alloy microstructure and, consequently, its strength. Alloy 600 is an austenitic nickel-based superalloy with 72% nickel, 14-17% chromium and 6-10% iron and it is commonly used in structures and components that work in aggressive environments. The grain size plays a significant role in the mechanical properties in this alloy; so, it is important to understand how processing techniques modify the microstructure of the material. In fact, ECAP is a processing technique involving the application of severe plastic deformation (SPD) used in the manufacture of metals and alloys with ultra-fine grains (UFG) and therefore with extraordinary combinations of both high strength and high ductility [1]. For the research, alloy 600 rods, supplied by Multialloy, with 8 mm diameter, were heat treated at 1200 °C for 6 h (solution), as shown in Figs. 1a and 1b, to achieve a larger grain size. The generated products were machined to the final dimensions of the specimen (6 X 6 X 25 mm) shown in Fig. 1c and then processed by ECAP, at room temperature using route A, in a D2 tool steel die, whose angles Φ and Ψ are 120° and 0° (Fig. 1d). Samples were pressed repetitively through a total of three passes, the microstructural aspect of the samples after each pass are shown in Figs. 2 and 3 with different magnifications. Metallographic preparations were made in the transverse, longitudinal and normal directions, TD, LD and ND of each sample. Sanding step with grit 320, 600 and 1200 were used. Polishing steps included 3 um- and 1 um-diamond paste and 0.05 um-alumina suspension and finally they were etched for optical examination using Marble’s etchant (10 g CuSO4, 50 ml HCl and 50 ml H2O). The micrographs were taken with OLYMPUS optical microscope model BX51M, with magnifications of 100x and 200x. The hardness tests were conducted in a Buehler Micromet 2103 microdurometer in the LD of the samples. For each measurement, a load of 500 g was applied for 15 s. Five separate measurements were taken on each sample at randomly selected points and then averaged. In Figs. 1a and 1b, it is possible to see only 1 phase, a solid solution of Ni-Cr-Fe, a coarsed grain structure and annealing twins. There are slight changes in the microstructure after the first pass, some strain marks are seen. After the second and third passes the microstructure shows highly deformed grains, deformation and transition bands. The values of hardness (Tab. 1) show an increase after each pass. In summary, (1) the micrographs analysis shows all the transformations from an annealed state to a highly-deformed state; (2) the grains are yet elongated after 3 passes and possibly do not show an expected UFG structure; (3) deformation twinning is revealed and is possible to see strain marks, deformation and transition bands; (4) the hardness values increased due to the high strain imposed to the alloy.

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