Pearlitic reaction in Cu-10wt%Al alloy with Ag additions

The pearlitic reaction in Cu-10wt%Al alloy with additions of 4, 6, 8, and 10wt%Ag was studied using scanning electron microscopy, energy dispersive X-ray microanalysis, in situ X-ray diffractometry, and microhardness measurements. The results indicated that the presence of Ag changes the pearlitic phase microstructure and its mechanical properties, because of the influence of Ag in the pearlitic phase growth mechanism. (C) 2008 International Centre for Diffraction Data.

Ageing behavior in the Cu-10 wt.%Al and Cu-10 wt.%Al-4 wt.%Ag alloys

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influence of Ag additions on the activation energy for the reverse eutectoid reaction in Cu-Al alloys

The eutectoid transformation may be defined as a solid-state diffusion-controlled decomposition process of a high-temperature phase into a two-phase lamellar aggregate behind a migrating boundary on cooling below the eutectoid temperature. In substitutional solid solutions, the eutectoid reaction involves diffusion of the solute atoms either through the matrix or along the boundaries or ledges. The effect of Ag on the non-isothermal kinetics of the reverse eutectoid reaction in the Cu-9 mass%Al, Cu-10 mass%Al, and Cu-11 mass%Al alloys were studied using differential scanning calorimetry (DSC), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The activation energy for this reaction was obtained using the Kissinger and Ozawa methods. The results indicated that Ag additions to Cu-Al alloys interfere on the reverse eutectoid reaction, increasing the activation energy values for the Cu-9 mass%Al and Cu-10 mass%Al alloys and decreasing these values for the Cu-11 mass%Al alloy for additions up to 6 mass%Ag. The changes in the activation energy were attributed to changes in the reaction solute and in Ag solubility due to the increase in Al content.

Reação de precipitação de Ag na liga Cu-8%Al-6%Ag

A reação de precipitação de prata na liga Cu-8%Al-6%Ag foi estudada usando medidas de variação da microdureza com a temperatura e o tempo de envelhecimento, difratometria de raios X (DRX), calorimetria exploratória diferencial (DSC), microscopia eletrônica de varredura (MEV). Os resultados obtidos indicaram que o mecanismo da reação de precipitação da prata é um processo controlado pela difusão da prata e a velocidade desta reação atinge um máximo em torno de 500°C.

Thermal behavior of the Cu-10 mass%Al and Cu-10 mass%Al-4 mass%Ag alloys

The thermal behavior of the Cu-10 mass%Al and Cu-10 mass% Al-4 mass%Ag alloys was studied using classical differential thermal analysis (DTA), optical microscopy (OM) and X-ray diffractometry (XRD). The DTA curves were obtained for annealed and quenched samples. The results indicated that the presence of silver introduces new thermal events, associated to the formation of a silver-rich phase, to the shift of the equilibrium concentration to higher A1 contents and to the decomposition of the silver-rich phase in the same temperature range of the beta(1) phase decomposition.

Biological leaching of Mn, Al, Zn, Cu and Ti in an anaerobic sewage sludge effectuated by Thiobacillus ferrooxidans and its effect on metal partitioning

The chemical fractionation and bioleaching of Mn, At, Zn, Cu and Ti in municipal sewage sludge were investigated using Thiobacillus ferrooxidans as leaching microorganism. As a result of the bacterial activity, ORP increase and pH reduction were observed. Metal solubilization was accomplished only in experimental systems supplemented with energy source (Fe(II)). The solubilization efficiency approached similar to80% for Mn and Zn, 24% for Cu, 10% for At and 0.2% for Ti. The chemical fractionation of Mn, At, Zn, Cu and Ti was investigated using a five-step sequential extraction procedure employing KNO3. KF, Na4P2O7, EDTA and HNO3. The results show that the bioleaching process affected the partitioning of Mn and Zn, increasing its percentage of elution in the KNO3 fraction while reducing it in the KF, Na4P2O7 and EDTA fractions. No significant effect was detected on the partitioning of Cu and Al. However, quantitatively the metals Mn, Zn, Cu and At were extracted with higher efficiency after the bacterial activity. Titanium was unaffected by the bioleaching process in both qualitative and quantitative aspects. (C) 2002 Elsevier B.V. Ltd. All rights reserved.

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.

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.

Preparation of Fe-Cr-P-Co amorphous alloys by electrodeposition

The effects of bath composition and electroplating conditions on structure, morphology, and composition of amorphous Fe-Cr-P-Co deposits on AISI 1020 steel substrate, priorly plated with a thin Cu deposit, were investigated. The increase of charge density activates the inclusion of Cr in the deposit. However, above specific values of the charge density, which depend on the deposition current density, the Cr content in the deposit decreases. This Cr content decreasing is probably due to the significant hydrogen evolution with the increasing of deposition cur-rent and charge density. The effect of charge density on the content of Fe and Co is not clear. However, there is a tendency of increasing of Fe content and decreasing of Co content with the raising of current density. The Co is more easily deposited than the P, and its presence results in a more intense inhibition effect on the Cr deposition than the inhibition effect caused by P presence. Scanning electron microscope (SEM) analysis showed that Co increasing in the Fe-Cr-P-Co alloys analyzed does not promote the susceptibility to microcracks, which led to a good quality deposit. The passive film of the Fe-Cr-P-Co alloy shows a high ability formation and high protective capacity, and the results obtained by current density of corrosion, j(cor), show that the deposit with addition of Co, Fe31Cr11P28Co30, presents a higher corrosion resistance than the deposit with addition of Ni, Fe54Cr21P20Ni5. (C) 2004 Published by Elsevier B.V.

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.

Thermal behavior of the Cu-22.55 at.%Al alloy with small Ag additions

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Completeness of beta-phase decomposition reaction in Cu-Al-Ag alloys

The completeness of beta-phase decomposition reaction in the Cu-11wt%Al-xwt%Ag alloys (x = 0, 1, 2, and 3) was studied using differential scanning calorimetry (DSC), X-ray diffractometry (XRD), and optical microscopy (OM). The results indicated that beta-phase transformations are highly dependent on cooling rate and on the presence of Ag. on slow cooling, the silver presence prevents the beta- and beta(1)-phase decomposition; thus, inducing the martensitic phase formation. After rapid cooling, a new thermal event is observed and the reverse martensitic transformation is shifted to lower temperatures.

Influence of Ag addition on the thermal behavior of the Cu-11 mass% Al alloy

In this work the influence of Ag additions on the thermal behavior of the Cu-11 mass% Al alloy was studied using differential scanning calorimetry, in situ X-ray diffractometry and scanning electron microscopy. The results indicated that changes in the heating rate shift the peak attributed to alpha phase formation to higher temperatures, evidencing the diffusive character of this reaction. The activation energy value for the alpha phase formation reaction, obtained from a non-isotherm kinetic model, is close to that corresponding to Cu atoms self diffusion, thus confirming that this reaction is dominated by Cu atoms diffusion through the martensite matrix.