Qualitative and quantitative characterization of aluminium alloys after corrosion testing

The 2024 and 7050 aluminium alloys used as aircraft components were subjected to laboratory corrosion tests in sodium chloride solution, Light-microscope examinations make it possible to characterise morphological aspects of the localised corrosion. Image analysis was used to determine both depth and width of pits over corroded surfaces. It has been concluded that the annealing could reduce the pit growth in both alloys, by means of grains recrystallization or recovery. The 2024 alloy also tends to present an exfoliation mechanism, mainly throughout non-recrystallized and recrystallized grain boundaries, increasing the width and sustaining the depth of pit cavities during exposition to saline atmosphere. SEM and EDS analysis reveal the morphology and elemental distribution of the corrosion products formed after immersion corrosion test. Some of these products were identified by X-ray diffraction analysis. For 2024, Al(OH)(3), MS(OH)(2) and Cu2O were found. AI(OH)(3) and Cu2O were also found in 7050 samples.

Preparation of Ni-Ti-Mo and Ni-Ti-Mo-Zr Alloys by High-Energy Ball Milling and Subsequent Hot Pressing

This work discusses on the preparation of Ni-45Ti-5Mo, Ni-40Ti-10Mo and Ni-46Ti-2Mo-2Zr (at-%) alloys by high-energy ball milling and hot pressing, which are potentially attractive for dental and medical applications. The milling process was performed in stainless steel balls (19mm diameter) and vials (225 mL) using a rotary speed of 300rpm and a ball-to-powder weight ratio of 10:1. Hot pressing under vacuum was performed in a BN-coated graphite crucible at 900 degrees C for 1 h using a load of 20 MPa. The milled and hot-pressed materials were characterized by X-ray diffraction, electron scanning microscopy, and electron dispersive spectrometry. Peaks of B2-NiTi and Ni4Ti3 were identified in XRD patterns of Ni-45Ti-5Mo, Ni-40Ti-10Mo and Ni-46Ti-2Mo-2Zr powders milled for 1h. The NiTi compound dissolved small Mo amounts lower than 4 at%, which were measured by EDS analysis. Moreover, it was identified the existence of an unknown Mo-rich phase in microstructures of the hot-pressed Ni-Ti-Mo alloys.

Wear resistance of experimental titanium alloys for dental applications

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Structural Evaluation of Mechanically Alloyed (67-x)Ti-xZr-22Si-11B Powders

The present work reports on the structural evaluation of mechanically alloyed Ti-xZr-22Si-11B (x = 5, 7, 10, 15 and 20 at-%) powders. Milled powders and hot-pressed alloys were characterized by X-ray diffraction, electron scanning microscopy, and electron dispersive spectrometry. The Si and B atoms were preferentially dissolved into the Ti and Zr lattices during ball milling of Ti-xZr-22Si-11B (x = 7, 10, 15 and 20 at-%) powders, and extended solid solutions were achieved. The displacement of Ti peaks was more pronounced to the direction of lower diffraction angles with increasing Zr amounts in mechanically alloyed Ti-Zr-Si-B powders, indicating that the Zr atoms were also dissolved into the Ti lattice.

Comparison of stress distribution between complete denture and implant-retained overdenture-2D FEA

The aim of this study was to compare the stress distribution induced by posterior functional loads on conventional complete dentures and implant-retained overdentures with different attachment systems using a two-dimentional Finite Element Analysis (FEA-2D). Three models representative of edentulous mandible were constructed on AutoCAD software; Group A (control), a model of edentulous mandible supporting a complete denture; Group B, a model of edentulous mandible supporting an overdenture over two splinted implants connected with the bar-clip system; Group C, a model of edentuluos mandible supporting an overdenture over two unsplinted impants with the O-ring system. Evaluation was conducted on Ansys software, with a vertical force of 100 N applied on the mandibular left first molar. When the stress was evaluated in supporting tissues, groups B (51.0 MPa) and C (52.6 MPa) demonstrated higher stress values than group A (10.1 MPa). Within the limits of this study, it may be conclued that the use of an attachment system increased stress values; furthermore, the use of splinted implants associated with the bar-clip attachment system favoured a lower stress distribution over the supporting tissue than the unsplinted implants with an O-ring abutment to retain the manibular overdenture.

Mechanical, physical, and chemical characterization of Ti-35Nb-5Zr and Ti-35Nb-10Zr casting alloys

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Metallomic study on plasma samples from Nile tilapia using SR-XRF and GFAAS after separation by 2D PAGE: initial results

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Analytical approach to the metallomic of Nile tilapia (Oreochromis niloticus) liver tissue by SRXRF and FAAS after 2D-PAGE separation: Preliminary results

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

Influence of iron addition on the microstructure and the electrochemical corrosion of Al-Zn-Mg alloys

The effect of Fe addition on the microstructural properties and the corrosion resistance of Al-Zn-Mg alloys submitted to different heat treatments (cast, annealed and aged), has been studied in chloride solutions using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), cyclic polarization (CP) and open circuit potential (o.c.p.) measurements. The presence of 0.3% Fe in the alloy limited the growth of the MgZn2 precipitates, both in the annealed and in the quenched specimens. No effect of Cr on the grain size in the presence of Fe was found because of the accumulation of Cr in the Fe-rich particles. Fe in the Al-Zn-Mg alloys also made them more susceptible to pitting. Pitting occurred mainly near the Fe-rich particles both, under o.c.p. conditions in O-2-saturated solutions and during the CP.

Electrochemical studies of copper-aluminum-silver alloys in 0.5 M H2SO4

The electrochemical behavior in 0.5 M H2SO4 at 25 degreesC of a Cu-Al(9.3 wt%)-Ag(4.7 wt%) alloy submitted to different heat treatments and an annealed Cu- Al(9.7 wt%)-Ag(34.2 wt%) were studied by means of open circuit potential (E-mix) measurements, potentiodynamic polarizations and cyclic voltammetry. SEM and EDX microanalysis were used to examine the changes caused by the electrochemical perturbations. The steady state potentials observed for the studied samples were correlated in terms of the phases present in the alloys surface. The resulting E/I potentiodynamic profiles were explained in terms of the potentiodynamic behavior of pure copper and pure silver. The presence of aluminum decreased the extent of copper oxidation. In the apparent Tafel potential region, two anodic Tafel slopes were obtained: 40 mV dec(-1) in the low potential region and 130 mV dec(-1) in the high potential region, which were related with the electrochemical processes involving copper oxidation. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

Kinetics of Ag-rich precipitates formation in Cu-Al-Ag alloys

The kinetics of Ag-rich precipitates formation in the Cu-2 wt.% Al alloy with additions of 2, 4, 6, 8, 10 and 12 wt.% Ag was studied using microhardness changes with temperature and time, differential scanning calorimetry (DSC), differential thermal analysis (DTA), scanning electron microscopy (SEM), optical microscopy (OM), energy dispersive X-ray analysis (EDX) and X-ray diffractometry (XRD). The results indicated that an increase in the Ag content decreases the activation energy for Ag-rich precipitates formation, and that it is possible to estimate the values of the diffusion and nucleation activation energies for the Ag precipitates. (C) 2004 Elsevier B.V. All rights reserved.

Thermal behavior of Cu-Al alloys near the alpha-Cu-Al solubility limit

The thermal behavior of Cu-Al alloys with 17, 19 and 21 at.%Al was examined by differential thermal analysis (DTA), differential scanning calorimetry (DSC), X-ray diffractometry (XRD), optical microscopy (OM) and scanning electron microscopy (SEM). The presence of the gamma phase (Al4Cu9) was clearly detected for the Cu-19 at.%Al alloy and caused the alpha (2) phase disordering process in two stages. The tendency to increase the alpha (2) dissolution precipitates with the increase in the Al content seems to be reverted for compositions at about 21 at.%Al and the heating/cooling ratio seems to influence the thermal response of this process. The presence of the endothermic peak corresponding to the beta (1)--> beta transformation depends on an incomplete beta decomposition reaction. The variation of the heating rate showed that the beta (1)-->(alpha+gamma (1)) decomposition is the dominant reaction for alloys containing 19 and 21 at.%Al.

Diffusion and interface controlled reactions in alpha-(Cu-Al-Ag) alloys

The isothermal kinetics of Ag precipitation was studied in Cu-Al-Ag alloys with concentrations ranging from 2 to 8 wt.%Al and 2 to 12 wt.%Ag, using scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDX) and microhardness measurements. The results indicated a change in the precipitates growing mechanism from diffusion to interface controlled process, probably due to a change in the nature of the interface with the Ag and Al enrichment of the precipitates. (C) 2006 Elsevier B.V. All rights reserved.

Electrochemical behaviour of heat-treated Al-Zn-Mg alloys in chloride solutions containing sulphate

The electrochemical corrosion and passivation of Al-5Zn-1.7Mg-0.23Cu-0.053Nb alloys, submitted to different heat treatments (cold-rolled, annealed, quenched and aged, and quenched in two steps and aged), in sulphate-containing chloride solutions, has been studied by means of cyclic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS). The cyclic polarization curves showed that sulphate addition to the chloride solution produced a poor reproducible shift of the breakdown potential to more positive potentials. The repassivation potentials, much more reproducible, and practically separating the passive from the pitting potential region, were slightly displaced in the negative direction with that addition. When the alloys were potentiodynamically polarized in the passive potential region, sulphate was incorporated in the oxide film, thus precluding chloride ingress. In addition, Zn depletion was favoured, whereas Mg losses were avoided. Different equivalent circuits corresponding to different alloys and potentials in the passive and pitting regions were employed to account for the electrochemical processes taking place in each condition. This work shows that sulphate makes these alloys more sensitive to corrosion, increasing the fracture properties of the surface layer and favouring the pitting attack over greater areas than chloride alone. (C) 2002 Elsevier B.V. Ltd. All rights reserved.

Precipitation reaction in alpha-Cu-Al-Ag alloys

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