THE INFLUENCE OF THE ELECTROCHEMICAL TREATMENT ON CU-AL-AG ALLOYS IN DEAERATED 0.5M NAOH

The effect of consecutive cyclic polarization in de-aerated 0.5 M NaOH solutions on the surface microstructure of mechanically polished Cu-Al-Ag alloys of different compositions and heat treatments has been studied using optical microscopy, SEM and EDS. The current peaks of the cyclic polarization curves do not depend on the alloy composition in the composition range studied. The repetitive potential scans between H2 and O2 evolution in alkaline media lead to preferential dissolution of aluminium, the roughness and phase composition of the surface of the alloys changing significantly. The quasistationary I-E curves of the different Cu-Al-Ag alloys studied consist in the superposition of the quasistationary I-E curves of high-purity Cu and Ag, the EDS microanalysis showing that aluminium is not present on the surface of the alloy in these conditions.

Kinetics of eutectoid decomposition in Cu-Al and Cu-Al-Ag alloys

The kinetics of eutectoid decomposition beta(1)' --> gamma(2) + (alpha + gamma(2)) in Cu-12.86 wt% Al and Cu-12.84 wt% Al-1.98 wt% Ag alloys was studied by hardness measurements, using the Johnson-Mehl-Avrami equation. The results indicate that the presence of silver seems to influence the nucleation rate and the activation energy of the reaction.

Gamma phases in Cu-Al alloys and the influence of a square shaped phase in the electrochemical behavior of a Cu-13.6wt% Al alloy

The electrochemical behavior of Cu-xAl alloys, with 11 wt%less than or equal to x less than or equal to 15wt%, in 0.5 M H2SO4 was studied by means of open-circuit potential decay measurements, quasi-stationary and fast cyclic voltammetry, and electrochemical impedance spectroscopy. Some of the alloys (x less than or equal to 14%), when quenched formed martensitic structures. Alloys with greater than or equal to 13% showed a little square-shaped phase when quenched from temperatures around 800 degrees C. It was observed that in sulfuric medium, these formations were dealuminized differently than the martensitic phase. The values of the rest potentials are more influenced by the heat treatment rather than by the alloy composition. An anodic Tafel slope of ca. 60 mV/decade was observed for all the alloys, independently of the heat treatment. This is explained in terms of a competition between two processes: copper oxidation and copper(I) deproportionation. In the cyclic voltammetric experiments it was observed an anodic current peak, related with copper oxidation with a possible formation of some interfacial species, and a cathodic current peak during the reverse potential scan, associated with the reduction of soluble species and/or of the film. The AC Impedance data were interpreted in terms of electric equivalent circuits.

Thermal behavior of alpha-(Cu-Al-Ag) alloys

Thermal behavior of alpha-(Cu-Al-Ag) alloys, i.e. alloys with composition less than about 8.5 mass% Al, was studied using differential scanning calorimetry (DSC), differential thermal analysis (DTA), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffractometry (XRD). The results indicated that the presence of silver introduces new thermal events ascribed to the formation of a silver-rich phase and, after addition higher amounts than 8 mass% Ag to the Cu-8 mass% Al alloy it is possible to observe the formation of the gamma(1) phase (Al4Cu9), which is only observed in alloys containing minimum of 9 mass% Al. These results may be attributed to some Ag characteristics and its interaction with Cu and Al.

Effect of Ag concentration on the thermal behavior of the Cu-10 mass% Al and Cu-11 mass% Al alloys

In this work the effect of Ag concentration on the thermal behavior of the Cu-10 mass% Al and Cu-11 mass% Al alloys with additions of 4, 6, 8 and 10 mass% Ag was studied using differential scanning calorimetry (DSC), in situ X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results showed that for the Cu-10 mass% Al alloy Ag addition induce the beta'(1) phase formation and for the Cu-11 mass% Al alloy these additions increase the amount of martensite formed on quenching and decrease the stability range of this phase on heating.

Martensite aging kinetics in the Cu-10 wt.%Al and Cu-10 wt.%Al-10 wt.%Ag alloys

The martensite aging kinetics in the Cu-10 wt.%Al and Cu-10 wt.%Al-10 wt.%Ag alloys was studied using microhardness measurements, classical differential thermal analysis (DTA), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and in-situ high-temperature X-ray diffractometry (XRD). The results for the Cu-10%Al alloy indicated a process dominated by the martensite ordering assisted by migration of quenched-in vacancies and followed by the consumption of the α phase. For the Cu-10%Al-10%Ag alloy the dominant process is the consumption of the α phase associated with a decrease in the ordering degree of the martensitic phase. © 2007 Springer Science+Business Media, LLC.

Correlação da coalescência de microcavidades com as propriedades mecânicas e elétricas de fios para Tx e Dx de energia elétrica da liga base Al-0,5%Cu-[0,24-0,28]%Fe modificada com teores de silício

Neste trabalho, é feita uma tentativa para estabelecer a influência dos teores [0,5; 0,7 e 0,9]%Si, como agentes modificadores da liga Al-0,05%Cu-[0,24-0,28]%Fe, avaliada através de aspectos que levaram em conta parâmetros operacionais de vazamentos unidirecionais horizontais tais como velocidades (Vs) e taxas de solidificação (Tx). Após operações de corte e usinagem foram obtidos perfis cilíndricos, com diâmetros de 9,5mm e comprimento de 120mm, a partir dos quais, após operações de trabalho à frio, chegou-se a fios com diâmetros de 2,7; 3,0; 3,8 e 4,0mm. Estes perfis foram submetidos à caracterização elétrica, com base na condutividade elétrica, à caracterização mecânica, com base em ensaios tensão/deformação enfatizando o alongamento, e a caracterização estrutural em seções longitudinais, com ênfase na distribuição das partículas de segunda fase e no aspecto da fratura, na qual a metodologia de avaliação das dimensões das microcavidades se utiliza da razão do cumprimento (L) pela largura (W).

Efeito de adições de Ni e Mg sobre o comportamento térmico, mecânico e elétrico de ligas Al-Cu-Fe solidificadas unidirecionalmente

Este trabalho estudou a influência dos teores dos solutos Mg e Ni na modificação das propriedades térmicas, elétricas e mecânicas de uma liga Al-Cu-Fe para aplicação como condutor de energia elétrica. Para a realização do presente estudo, as ligas foram obtidas por fundição unidirecional horizontal, a partir da base do alumínio de pureza comercial com adição dos teores 0,05%p Cu e [0,24 a 0,28]%p Fe. Tal base foi modificada em uma primeira etapa com teores de 0,45, 0,60 e 0,80%p Mg. As ligas obtidas com estes teores tiveram suas propriedades estudadas para que se selecionasse um teor de Mg para posterior adição de Ni à liga. O estudo destas propriedades na primeira etapa passou pela análise das propriedades térmicas: velocidade de solidificação (V_L) e taxa de resfriamento (Ṫ). A caracterização elétrica estudou a propriedade condutividade elétrica (φ) e o levantamento das propriedades mecânicas: limite de resistência à tração (σ) e microdureza Vickers (HV). A liga com adição de Ni passou por tratamentos térmicos de envelhecimento, por 1, 4 e 8h. Estas amostras foram analisadas em um microscópio eletrônico de varredura - MEV pelos sinais de elétrons retroespalhados – ERE e espectroscopia de energia dispersiva – EDS. Como resultados do estudo, encontrou-se que adições de Mg influenciaram significativamente a viscosidade das ligas, elevando as velocidades de solidificação nos instantes finais. Os ensaios de microdureza das amostras envelhecidas mostraram que houve um acréscimo significativo de dureza na quarta hora de envelhecimento, da mesma forma que as análises de EDS mostraram que a concentração de Ni também elevou-se nesta condição de tratamento.

Espectros de raios-x em MEV indicam associação entre Al e Si em plantas acumuladoras de Al do Cerrado

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

SVET, SKP and EIS study of the corrosion behaviour of high strength Al and Al-Li alloys used in aircraft fabrication

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

As-synthesized TEA-BEA zeolite: Effect of Si/Al ratio on the Knoevenagel condensation

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

A complex structure in the (beta+gamma(0)) region of the Cu-Al alloys

The identification, characterization and stability range of the phases present in a series of Cu-Al alloys, with Al content from 11.0 to 15.0 wt.%, were studied by Differential Thermal Analysis (DTA), Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Selected Area Electron Diffraction (SAED), Auger Electron Spectroscopy (AES), Energy Dispersive X-Ray Spectroscopy (EDX) and X-Ray Diffraction (XRD). In some alloys and in a temperature range from 790 degrees C to 850 degrees C the presence of black spots exhibiting regular shapes and an homogeneous distribution was noticed through metallographic microscopy. Data from TEM and AES indicate that these spots are made of two monocrystalline phases having different Al contents and a crystallographic orientation relationship. (C) 1998 Elsevier B.V. S.A. All rights reserved.

Does the casting mode influence microstructure, fracture and properties of different metal ceramic alloys?

The aim of the present study was to evaluate the tensile strength, elongation, microhardness, microstructure and fracture pattern of various metal ceramic alloys cast under different casting conditions. Two Ni-Cr alloys, Co-Cr and Pd-Ag were used. The casting conditions were as follows: electromagnetic induction under argon atmosphere, vacuum, using blowtorch without atmosphere control. For each condition, 16 specimens, each measuring 25 mm long and 2.5 mm in diameter, were obtained. Ultimate tensile strength (UTS) and elongation (EL) tests were performed using a Kratos machine. Vickers Microhardness (VM), fracture mode and microstructure were analyzed by SEM. UTS, EL and VM data were statistically analyzed using ANOVA. For UTS, alloy composition had a direct influence on casting condition of alloys (Wiron 99 and Remanium CD), with higher values shown when cast with Flame/Air (p < 0.05). The factors "alloy" and "casting condition" influenced the EL and VM results, generally presenting opposite results, i.e., alloy with high elongation value had lower hardness (Wiron 99), and casting condition with the lowest EL values had the highest VM values (blowtorch). Both factors had significant influence on the properties evaluated, and prosthetic laboratories should select the appropriate casting method for each alloy composition to obtain the desired property.

Manufacturing and characterization of amorphous silicon alloys passivation layers for silicon hetero-junction solar cells

Nel presente lavoro di tesi magistrale sono stati depositati e caratterizzati film sottili (circa 10 nm) di silicio amorfo idrogenato (a-Si:H), studiando in particolare leghe a basso contenuto di ossigeno e carbonio. Tali layer andranno ad essere implementati come strati di passivazione per wafer di Si monocristallino in celle solari ad eterogiunzione HIT (heterojunctions with intrinsic thin layer), con le quali recentemente è stato raggiunto il record di efficienza pari a 24.7% . La deposizione è avvenuta mediante PECVD (plasma enhanced chemical vapour deposition). Tecniche di spettroscopia ottica, come FT-IR (Fourier transform infrared spectroscopy) e SE (spettroscopic ellipsometry) sono state utilizzate per analizzare le configurazioni di legami eteronucleari (Si-H, Si-O, Si-C) e le proprietà strutturali dei film sottili: un nuovo metodo è stato implementato per calcolare i contenuti atomici di H, O e C da misure ottiche. In tal modo è stato possibile osservare come una bassa incorporazione (< 10%) di ossigeno e carbonio sia sufficiente ad aumentare la porosità ed il grado di disordine a lungo raggio del materiale: relativamente a quest’ultimo aspetto, è stata sviluppata una nuova tecnica per determinare dagli spettri ellisometrici l’energia di Urbach, che esprime la coda esponenziale interna al gap in semiconduttori amorfi e fornisce una stima degli stati elettronici in presenza di disordine reticolare. Nella seconda parte della tesi sono stati sviluppati esperimenti di annealing isocrono, in modo da studiare i processi di cristallizzazione e di effusione dell’idrogeno, correlandoli con la degradazione delle proprietà optoelettroniche. L’analisi dei differenti risultati ottenuti studiando queste particolari leghe (a-SiOx e a-SiCy) ha permesso di concludere che solo con una bassa percentuale di ossigeno o carbonio, i.e. < 3.5 %, è possibile migliorare la risposta termica dello specifico layer, ritardando i fenomeni di degradazione di circa 50°C.

Chemical composition modification of casting aluminium alloys for engine applications

The research activities were focused on evaluating the effect of Mo addition to mechanical properties and microstructure of A354 aluminium casting alloy. Samples, with increasing amount of Mo, were produced and heat treated. After heat treatment and exposition to high temperatures samples underwent microstructural and chemical analyses, hardness and tensile tests. The collected data led to the optimization of both casting parameters, for obtaining a homogeneous Mo distribution in the alloy, and heat treatment parameters, allowing the formation of Mo based strengthening precipitates stable at high temperature. Microstructural and chemical analyses highlighted how Mo addition in percentage superior to 0.1% wt. can modify the silicon eutectic morphology and hinder the formation of iron based β intermetallics. High temperature exposure curves, instead, showed that after long exposition hardness is slightly influenced by heat treatment while the effect of Mo addition superior to 0,3% is negligible. Tensile tests confirmed that the addition of 0.3%wt Mo induces an increase of about 10% of ultimate tensile strength after high temperature exposition (250°C for 100h) while heat treatments have slight influence on mechanical behaviour. These results could be exploited for developing innovative heat treatment sequence able to reduce residual stresses in castings produced with A354 modified with Mo.