Estudo da influência do agente nucleante )ALTi5%B1%) na microestrutura de chapas AA8011 obtidas por lingotamento contínuo

The aluminum includes several properties with excellent relation between weight and mechanical resistance. With technological advances, increasingly demand the development of new alloys and other production processes in order to reduce the cost of production and insert these new alloys in broader applications. The process of continuous caster (TRC promoted the unite of the aluminum smelting process with the first stage of rolling, making it most economical through the merger these two phases besides transform the continuous casting process. The AA8xxx series is one of the most versatile aluminum alloys and the most often used in continuous caster process provided a great potential application in the market. In order to further, optimize the process it is necessary to increase awareness of the aluminum solidification phenomena associated with the addition of grain refiner, and control of some aluminum production parameters in the process (production rate, metal temperature, etc.). In this study, AA8011 alloy samples were taken in the raw state obtained by the continuous casting process. The samples were laminated to a thickness of 7mm during the process itself and analyzed at three points along its width by microstructural analysis throughout its thickness, the variation rate of addition of the grain refiner in order to assess the influence of this addition with crystallographic formation and some formation of intermetallic precipitates during the solidification. Through this work, it was possible to improve the knowledge related to the addition of refiner with the monitoring of these production processes

Measuring the critical resolved shear stresses in Mg alloys by instrumented nanoindentation

One of the main limiting factors in the development of new magnesium (Mg) alloys with enhanced mechanical behavior is the need to use vast experimental campaigns for microstructure and property screening. For example, the influence of new alloying additions on the critical resolved shear stresses (CRSSs) is currently evaluated by a combination of macroscopic single-crystal experiments and crystal plasticity finite-element simulations (CPFEM). This time-consuming process could be considerably simplified by the introduction of high-throughput techniques for efficient property testing. The aim of this paper is to propose a new and fast, methodology for the estimation of the CRSSs of hexagonal close-packed metals which, moreover, requires small amounts of material. The proposed method, which combines instrumented nanoindentation and CPFEM modeling, determines CRSS values by comparison of the variation of hardness (H) for different grain orientations with the outcome of CPFEM. This novel approach has been validated in a rolled and annealed pure Mg sheet, whose H variation with grain orientation has been successfully predicted using a set of CRSSs taken from recent crystal plasticity simulations of single-crystal experiments. Moreover, the proposed methodology has been utilized to infer the effect of the alloying elements of an MN11 (Mg–1% Mn–1% Nd) alloy. The results support the hypothesis that selected rare earth intermetallic precipitates help to bring the CRSS values of basal and non-basal slip systems closer together, thus contributing to the reduced plastic anisotropy observed in these alloys

Comments on “High-temperature creep resistance and effects on the austenite reversion and precipitation of 18 Ni (300) maraging steel” by dos Reis et al. [Materials Characterization 107 (2015) 350- 357]

This letter attempts to comment on an article by dos Reis et al., in the aspects of creep considerationand chemical analysis in maraging steels.

Oxidation and abrasive wear of Fe-Si and Fe-Al intermetallic alloys

In the present work, intermetallic alloys Fe-Si and Fe-Al (Fe(3)Si-C-Cr and Fe(3)Al-C), produced by induction melting, were evaluated regarding their oxidation and abrasive resistance. The tests performed were quasi-isothermal oxidation, cyclic oxidation, and dry sand/rubber wheel abrasion. As reference, the ASTM A297-HH grade stainless steel was tested in the same conditions. In the oxidation tests, the Fe-Al based alloy presented the lowest oxidation rate, and the Fe-Si based alloy achieved the best results in the abrasion test, showing better performance than the HH type stainless steel.

ASTM A923-Practice A application to identify intermetallic phases in a UNS S32750 superduplex welded joint

Duplex and superduplex stainless steels present superior mechanical and corrosion properties when compared to usual stainless steels. This superiority is based on chemical composition when in a balanced microstructure (approximately 50% of ferrite). During welding, changes may occur in both, the chemical composition and volume fraction of phases in the material, which may generate the presence of intermetallic phases and, as a consequence, modify the mechanical and corrosion properties of this group of stainless steels. The objective of this work is to apply ASTM A923- Practice A to verify the presence of intermetallic phases in welded joints of UNS 32750 su-perduplex stainless steel. Tubes of UNS 32750, with external diameters of 18 and 44 mm and a thickness of 1.5 mm, were welded using orbital GTAW, with filler metal 25Cr-10Ni-4Mo and a diameter of 0.8 mm. The metal-based and welded joints were characterized by optical and scanning electron microscopy. The results showed that there was no precipitation of the intermetallic phase, such as sigma phase, detected by ASTM A923, but the HAZ of the two tubes studied presented small regions with chromium nitrides, which can also change the properties of welded joins.

A practical method for identifying intermetallic phase particles in aluminium alloys by electron probe microanalysis

Aluminium alloys that contain Si, Mg, Fe, Mn and/or Cu usually contain one or more types of intermetallic phases that are not readily distinguishable in the microstructure by conventional microscopy methods. It has thus been a challenge to develop a method that will unambiguously identify them. A practical approach has been developed that is based on an inherent linear relationship revealed for the overall distribution of any two elements in a precipitate/matrix geometry and the first-order approximation of electron probe microanalysis (EPMA) results. Application of this approach to a direct chill cast 6082 alloy is demonstrated, and its major limitations are discussed.

Intermetallic layer formation and influence in solder joints reliability

Dissertação de mestrado integrado em Materials Engineering

Study of the influence of grain size and precipitates on the electromagnetic losses in different grades of non-oriented fully processed electrical steel

The study was performed in the installations of OCAS, a Steel Research Centre of ArcelorMittal. Taking M32 steel (3.25%Si+0.9%Al) as the basis chemical composition and three different thicknesses (0.35, 0.5 and 0.65mm), different annealing conditions (temperature and time) have been applied in the laboratory simulator at St. Chély, France. The aim was to link annealing parameters, grain size and energy loss. It was determined the optimum annealing parameters to reach the lowest power losses for three different grades of non-oriented fully processed electrical steel. In addition, M250-50 samples having different magnetic behaviour (high and low losses) but the same grain size and texture, have been analyzed in terms of TEM observations of their precipitates, in the University of Marseille. The results reveal that a high amount of medium and big precipitates (&10 nm) worsen the magnetic properties of the material. The small precipitates (&10nm) do not have a strong influence on the magnetic properties. The presence of precipitates can have a great influence on the power losses and further work is clearly necessary.

Point defects and texture of Pd1-xInx sputtered intermetallic thin films

Pd1-xInx thin films (0.4 < x < 0.56) were prepared by radio frequency sputtering from a multi-zone target. The properties of these Hume-Rothery alloys were studied by X-ray diffractometry, electron probe microanalysis and scanning tunneling microscopy. The diffraction spectra were analyzed to obtain the intensity ratio of the (100) superlattice line to the (200) normal line, together with the variations of the lattice constant. The results ape explained quantitatively by a model based on point defects, i.e. Pd vacancies in In-rich films and Pd antisite atoms in Pd-rich films. In-rich films grow preferentially in the [100] direction while Pd-rich films grow preferentially in the [110] direction. The grains in indium-rich sputtered films appear to be enclosed in an atomically thick, indium-rich layer. The role of texture and the influence of point defects on electrical resistivity is also reported. (C) 1996 Elsevier Science Limited.

Fe-sulphate-rich evaporative mineral precipitates from the Rio Tinto, southwest Spain

The soluble metal sulphate salts melanterite, rozenite, rhomboclase, szornolnokite, copiapite, coquimbite, hexahydrite and halotrichite, together with gypsum, have been identified, some for the first time oil the banks of the Rio Tinto, SW Spain. Secondary Fe-sulphate minerals call form directly from evaporating acid, sulphate-rich Solutions as a result of pyrite oxidation. Chemical analyses of mixtures of these salt minerals indicate concentrations of Fe (up to 31 wt.%), Mg (up to 4 wt.%), Cu (up to 2 wt.%) and Zn (up to wt.%). These minerals are shown to act as transient storage Cor metals and can store on average up to 10% (9.5 - 11%) and 22% (20-23%) Zn and Cu respectively, of the total discharge of the Rio Tinto during the summer period. Melanterite and rozenite precipitates at Rio Tinto are only found in association with very acidic drainage waters (pH <1.0) draining directly from pyritic waste piles. Copiapite precipitates abundantly oil the banks of the Rio Tinto by (1) direct evaporation of the river water; or (2) as part of a paragenetic sequence with the inclusion of minor halotrichite, indicating natural dehydration and decomposition. The natural occurrences are comparable with the process of paragenesis from the evaporation of Rio Tinto river water under laboratory experiments resulting in the formation of aluminocopiapite, halotrichite, coquimbite, voltaite and gypsum.