DANIELA PASSARELO MOURA

DANIELA PASSARELO MOURA

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Analysis by optical microscopy and x-ray diffraction of composite Cu-Cr-Ag-Al2O3 synthesized using powder metallurgy
2017 - FONSECA, DANIELA P.M. da; MONTEIRO, WALDEMAR A.
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.
The microstructure and properties of copper with ceria nanoparticles addition
2019 - FONSECA, DANIELA P.; MONTEIRO, WALDEMAR A.
Copper-based composites strengthened by ceria nanoparticles were processed by conventional powder metallurgy: mixing (30 min and 46 rpm), compaction (cold, uniaxial, 1080 MPa for 10 s) and sintering (800˚C for 6 h in vacuum atmosphere of 10−5 torr). It was studied the microstructure (optical microscopy, scanning electron microscopy), X-ray diffraction with Rietveld refinement and some properties (electrical conductivity, Vickers hardness and fracture analysis) of the compositions 92 wt% Cu - 8 wt% CeO2 and 80 wt% Cu - 20 wt% CeO2. The results showed uniform phase distribution, low porosity and ceria disperse inside copper grain. In despite of properties, the composites had electrical conductivity of 38% IACS and 15% IACS and hardness of 69 and 88 HV5, respectively. The results of 92 wt% Cu - 8 wt% CeO2 composites were promising, and they are in according with actual literature.
Processamento, microestrutura e propriedades de compósitos à base de cobre reforçados com alumina
2018 - FONSECA, D.P.M. da; MONTEIRO, W.A.
O cobre e suas ligas são utilizados por suas boas propriedades físicas, a adição de fase cerâmica pode aumentar a resistência mecânica e a resistência ao desgaste sem causar grande perda na estabilidade térmica e condutividade elétrica. Este trabalho teve como objetivo processar por metalurgia do pó e estudar a microestrutura e propriedades de compósitos à base de cobre reforçados com alumina. As análises de MO, MEV e EDS indicaram boa distribuição das fases na matriz de cobre, boa coalescência das partículas formando superfície continua e baixa porosidade. O aumento da concentração de alumina diminuiu a condutividade elétrica, no entanto, proporcionou bom incremento na dureza do cobre puro.
Efeitos da adição de nanopartículas de céria na microestrutura e propriedades do cobre
2018 - FONSECA, D.P.M.; MONTEIRO, W.A.
O cobre é utilizado por suas boas propriedades físicas (alta condutividade elétrica e térmica, resistência à corrosão) e econômicas (facilidade de fabricação, custo de matéria prima mediano e reciclagem). No entanto, metais puros de alta condutividade elétrica são muito dúcteis e, para muitas aplicações, é requerido simultaneamente alta condutividade elétrica e resistência mecânica. O aumento da resistência mecânica do cobre pode ocorrer pela adição de fase de reforço, o que aumenta também a dispersão da nuvem de elétrons diminuindo a condutividade do material. A céria é um dos óxidos de terras raras mais utilizados devido a suas características como alto ponto de fusão e estabilidade química e térmica. Este trabalho teve como objetivo processar e estudar a microestrutura e propriedades (condutividade elétrica, dureza e fratura) dos compósitos 92% Cu 8% CeO2 e 80% Cu - 20% CeO2. As amostras foram processadas pela técnica de metalurgia do pó: pesagem, mistura (sem bolas por 30 min com frequência de rotação de 46 rpm), compactação (uniaxial à frio com pressão de 1080 Mpa por 10s) e sinterização (800°C por 6h com taxa de aquecimento de 10°C/min sob vácuo de 10 7 torr). Os pós de partida foram caracterizados por distribuição granulométrica, MEV/MET, EDS e DRX com refinamento Rietveld. Apresentaram valores de diâmetro médio de partícula de 39,86 μm (cobre) e < 25 nm (céria), resultados de microanálise EDS adequados (foram identificados apenas os elementos previstos) e resultados de DRX sem indicação de formação de fase indesejada e com tamanho de cristalitos nanométricos. As análises de MO, MEV e EDS indicaram distribuição uniforme das fases, boa coalescência das partículas formando superfície continua, baixa porosidade e fase de céria dispersa nos contornos de grão do cobre com algumas regiões aglomeradas. Os resultados de microanálise EDS não indicaram contaminação nem oxidação das amostras. Os difratogramas indicaram formação de fases isoladas. As amostras com 8% e 20% de céria apresentaram, respectivamente, densidade de 8,12 e 7,66 g/cm³, densidade relativa de 92% e 88% (em relação à amostra sinterizada de 100%Cu), condutividade elétrica de 38% e 15% IACS, condutividade elétrica relativa de 51% e 21%, dureza de 69 e 88 HV5 (677 e 863 MPa) e dureza relativa de 230% e 293%. As fratografias apresentaram, para ambos os compósitos, fratura mista (dúctil e frágil) e indicaram boa adesão entre a matriz metálica e o reforço cerâmico. As análises indicaram microestrutura adequada com boa dispersão de céria e boa densificação das partículas. Foi observado efetivo aumento na resistência mecânica, o compósito com 20% de céria apresentou dureza cerca de 3 vezes maior do que a do cobre, porém, em ambos os compósitos, o acréscimo da fase cerâmica acarretou na diminuição da condutividade elétrica. O compósito com 8% de céria foi o que apresentou melhor equilíbrio entre essas duas propriedades.
Processamento, microestrutura e propriedades de compósitos à base de cobre reforçados com alumina e céria
2018 - FONSECA, DANIELA P.M. da
Compósitos de matriz metálica combinam diferentes classes de materiais a fim de obter novas propriedades, superiores às dos materiais originais. A adição de partículas cerâmicas (reforço) em ligas de cobre pode melhorar suas propriedades mecânicas sem gerar grande perda na condutividade elétrica. Este trabalho teve como objetivo processar e estudar a microestrutura e propriedades (condutividade elétrica, dureza e fratura) de compósitos à base de cobre reforçados com alumina e céria. As amostras foram processadas pela técnica de metalurgia do pó: pesagem, mistura (sem bolas por 30min a 46 rpm), compactação (uniaxial à frio com pressão de 1080 Mpa por 10s) e sinterização (800°C por 6h sob vácuo de 10-5 torr). As análises de MO, MEV, EDS e DRX (com refinamento Rietveld) indicaram boa coalescência das partículas, formando superfície continua e com baixa porosidade. A alumina formou regiões aglomeradas da ordem de 20 μm, a céria ficou finamente dispersa nos contornos de grão do cobre com algumas regiões aglomeradas, o cromo formou regiões de cerca de 100 μm e não teve distribuição completamente uniforme ao longo da matriz, a prata formou solução sólida com o cobre e, durante o resfriamento lento, formou precipitados menores do que 5 μm uniformemente dispersos no interior dos grãos de cobre. Os compósitos apresentaram condutividade elétrica entre 15 e 40 %IACS, dureza entre 62 e 88 HV5 e as fractografias apresentaram fratura mista e regiões indicando boa adesão matriz-reforço. Em relação ao cobre puro, foi observado efetivo aumento na dureza (cerca de 2x), porém, em todos os compósitos, o acréscimo da fase cerâmica acarretou na diminuição da condutividade elétrica. Os compósitos de Cu-8%(Al2O3, CeO2) foram os que apresentaram melhor equilíbrio entre essas duas propriedades, com condutividade de 40 e 38 %IACS e dureza de 63 e 69 HV5.
Microstructural analysis of composite Cu-Cr-Ag-(CeO2, Al2O3) processing by powder metallurgy
2017 - FONSECA, DANIELA P.M. da; MONTEIRO, WALDEMAR A.
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.
Electrical conductivity and microstructural analysis of composite Cu-Ag-Cr-Al2O3 after sintering on powder metallurgy processing
2016 - FONSECA, DANIELA P.M. da; MONTEIRO, WALDEMAR A.
The aim of this work was to produce copper-chromium-silver alloys with alumina by powder metallurgy, forming a composite, keeping good mechanical (hardness test) and good electrical (electrical conductivity) properties. The elements are added to copper alloys with purpose to improve mechanical strength, ductility and thermal stability, without causing considerable damage in its shape, electrical and thermal conductivity. The metallic powders with alumina have been mixed for an appropriate time, compressed in uniaxial pressure and sintered at temperatures of 923K to 1073K in appropriate vacuum. The obtained alloys were characterized by electrical conductivity, optical microscopy, and Vickers hardness measurements. The steps performed in composites obtained by powder metallurgy processing indicate adequate mechanical resistance values (450 MPa) and, electrical conductivity in the range 0,216 ≤ σ ≤ 0,309 (μΩcm)-1 (35 to 45% IACS). Electrical conductivity measurements and analysis of microstructures by optical microscopy suggest that these composites are relevant to the application as electrical contact material used in consumer electronics devices.