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URI permanente para esta coleçãohttps://repositorio.fei.edu.br/handle/FEI/795
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Artigo de evento 1 Citação(ões) na Scopus Pit morphology and its microstructure relation in 850°C aged UNS S31803 (SAP 2205) duplex stainless steel(2003-07-24) Rodrigo Magnabosco; ALONSO-FALLEIROS, N.This work described the relationship between microstructure of UNS S 31803 (SAP 2205) aged at 850°C and pitting morphology after cyclic polarization in chloride aqueous solution. The initial material, solution treated for 30 minutes at 1120°C and water quenched, was aged at 850°C for periods up to 100 hours. Cyclic polarization in 3,5% NaCl aqueous solution was conducted on #600 grounded sample surfaces. After polarization, the samples were sectioned transversal and perpendicular to polarized surface to allow the inner view of pitting corrosion using scanning electron microscope. It was found that sigma phase formation after 850°C aging treatment reduced pitting potential, and pitting corrosion occurred as selective corrosion of chromium and molybdenum impoverished regions, like interfaces between sigma phase and metallic matrix.Artigo 2 Citação(ões) na Scopus New approach for applications of machinability and machining strength(2009-09-05) COPPINI, N. L.; Júlio Cesar Dutra; DOS SANTOSA, E. C.Purpose: The purpose of this paper is to present and discuss the machinability and machining strength concepts under a new viewpoint concerned with both their applications and how to measure then. Despite of the fact that to develop easy to cut steel is a very important task, this work take under consideration entire application of these properties for any kind of materials in terms of how aggressive it can be against the tool material. Design/methodology/approach: A new approach to measure machining strength property is proposed. The reliability of the proposed test was based on experimental data from the literature. The best way to apply machinability index and machining strength index is put forward. Otherwise, at this moment, the authors are doing experimental laboratory research to evaluate the best way to organize appropriate samples to attend different kind products for respective materials makers'. Findings: It was possible to conclude that machinability must be used by means of comparative tests as close as possible to shopping floor conditions. The main application is to select the best steel to be used for a specific cutting process workpart. Research limitations/implications: The main limitation is that the entire new viewpoint presented is very new for the materials makers. The authors must spread the ideas presented here to check the actual materials makers' resistance or acceptance of their applications. Originality/value: The proposed test is very simple and more reliable than that one already published. On the other hand, machining strength is a material intrinsic property. For this reason, it is best employed during easy to cut materials development and measured by a Coppini Index (CI) based on standard tests. As a material intrinsic property it is not related to a standard material. Machinability is supposed to be appropriated for process optimization and not for materials development or characterization. © Copyright by International OCSCO World Press. All rights reserved. 2009.- Fracture toughness of the eutectic alloy Al3Nb-Nb2Al(2003-08-05) TRIVENO RIOS, C.; FERRANDINI, P.; CARAM, R.Presenting high fracture toughness is a decisive condition to any structural material, and when considering brittle alloys, the Vickers indentation method to determine fracture toughness is an interesting alternative. Like many other intermetallics, the Al3Nb-Nb2Al eutectic alloy shows high strength at high temperatures and low fracture toughness at room temperature. Al3Nb-Nb2Al samples, both in the as-solidified condition and in the directionally solidified condition, had their hardness and fracture toughness determined by the Vickers indentation method. Lower values of hardness were found when higher loads were used, and fracture toughness was found to be about 2.0 MPa m1/2. The as-solidified condition is harder and less tough, and when fracture occurs, cracks always develop by cleavage. © 2003 Elsevier Science B.V. All rights reserved.
- International division of labour in product development activities: Towards a selective decentralisation?(2004-01-05) DIAS, A. V. C.; SALERNO, M. S.This paper aims to contribute to the debate on the international division of labour among headquarters and subsidiaries located in emerging markets, concerning product development (PD) activities. We argue that market proximity and technological sourcing, often claimed as reasons for decentralising PD activities, are not sufficient to explain some cases of integration of subsidiaries located in emerging markets in their headquarters' PD structures. We then propose that this integration may arise in order to reduce development time and costs; also, the integration of subsidiaries depends on their relationship with headquarters and on the role played by host and home governments. Finally, we present some proposals on how the division of labour occurs, concerning the development of platform and derivatives and the stages on the PD process. These propositions are based on case studies conducted in four major car assemblers in the last four years, examining their headquarters as well as their Brazilian subsidiaries.
- Influence of growth rate on the microstructure and mechanical behaviour of a NiAl-Mo eutectic alloy(2004-11-03) FERRANDINI, P.; BATISTA, W. W.; CARAM, R.The effect of the growth condition on the microstructure and mechanical behaviour of the NiAl-Mo eutectic alloy was investigated. Samples of the eutectic alloy were prepared using an arc furnace under argon atmosphere and then directionally solidified. The samples directionally solidified showed regular and aligned eutectic microstructure. Compression tests were performed at room temperature and 1173K. Vickers hardness was determined at several temperatures, from room temperature to 1150K. Mechanical properties of NiAl were also determined. Results showed that when the growth rate is gradually increased from 8 to 50mm/h the aligned microstructure presents higher fibre density, which leads to higher strength level at room temperature, while further increase in the growth rate causes the microstructure the loose regularity. NiAl presents a well defined mechanical behaviour transition, while the NiAl-Mo eutectic alloy softens almost linearly. The highest yield strength value of NiAl-Mo was found to be about 1200 and 300MPa at room temperature and 1173K, respectively. © 2004 Elsevier B.V. All rights reserved.
- Directional solidification, microstructure and properties of the Al3Nb-Nb2Al eutectic(2005-02-15) RIOS, C. T.; MILENKOVIC, S.; FERRANDINI, P. L.; CARAM, R.The Al-Nb system exhibits a eutectic transformation at 1595.2°C, which results in Al3Nb (D022) and Nb2Al (D8b) phases. This paper is concerned with the processing of this eutectic by directional solidification. Alloys were prepared by arc melting and directionally solidified in Bridgman-type equipment. The resulting samples were utilized to evaluate the solidification microstructure and morphology regarding the growth conditions. Eutectic microstructures obtained were regular with lamellar morphology. Variations of the growth rate showed that an increase in this parameter causes a decrease in the lamellar spacing. With further increase in the growth rate, eutectic cells were observed as a result of constitutional undercooling. Oxidation tests of eutectic microstructures showed that this alloy suffers severe microstructure instability, with growth kinetics of the oxide scale of linear type. This indicates that the Al in the Nb-Al eutectic alloy is insufficient to form protective oxide films, such as, α-Al2O3. Finally, the heat treatment in argon atmosphere showed that the eutectic alloy presents a high degree of microstructure stability at 1200°C. © 2004 Elsevier B.V. All rights reserved.
- Growth and characterization of the NiAl-NiAlNb eutectic structure(2005-02-15) FERRANDINI, P. L.; ARAÚJO, F. L. G. U.; BATISTA, W. W.; CARAM, R.Despite presenting potential as high-temperature structural material, the NiAl intermetallic compound cannot be easily employed due to its low room temperature fracture toughness and poor creep strength. A solution for such a problem is combining such a compound with other phase using a eutectic transformation, as in the case of the NiAl-NiAlNb eutectic structure. In this study, several samples containing Ni, Al and Nb were arc melted in order to evaluate the eutectic composition of this transformation, as well as the temperature at which it occurs. The resulting phases were the B2 NiAl and the Laves phase NiAlNb. It was found that the eutectic alloy occurs close to 16.0 at% Nb and the eutectic transformation temperature is 1487 °C. The amount of NiAl phase clearly decreases when the Nb content is raised. Thus, hypoeutectic alloys present NiAl dendrites with NiAlNb precipitated at the grain boundaries while hypereutectic alloys present primary dendrites of NiAlNb. The eutectic alloy was directionally solidified at growth rates varying from 5.0 to 50.0 mm/h. As expected, the lamellar spacing was found to decrease as the growth rate was increased. © 2004 Elsevier B.V. All rights reserved.
- Growth and microstructure evolution of the Nb2Al-Al 3Nb eutectic in situ composite(2005-03-05) RIOS, C. T.; FERRANDINI, P. L.; MILENKOVIC, V.; CARAM, R.In situ composite materials obtained by directional growth of eutectic alloys usually show improved properties, that make them potential candidates for high temperature applications. The eutectic alloy found in the Al-Nb system is composed of the two intermetallic phases Al3Nb (D022) and Nb2Al (D8b). This paper describes the directional solidification of an Al-Nb eutectic alloy using a Bridgman type facility at growth rates varying from 1.0 to 2.9 cm/h. Longitudinal and transverse sections of grown samples were characterized regarding the solidification microstructure by using optical and scanning electron microscopy, energy dispersive spectroscopy (EDS) and X-ray diffraction. Despite both phases being intermetallic compounds, the eutectic microstructure obtained was very regular. The results obtained were discussed regarding the effect of the growth rate on the microstructure, lamellar-rod transition and variation of phase volume fraction. © 2004 Elsevier Inc. All rights reserved.
- Surface segregation in SnO2-Fe2O3 nanopowders and effects in mössbauer spectroscopy(2005-06-01) CASTRO, R. H. R.; HIDALGO, P.; COAQUIRA, J. A. H.; BETTINI, J.; ZANCHET, D.; GOUVEA, D.SnO2-Fe2O3 nanopowders prepared by the polymeric precursor method were studied by combined conventional and high-resolution techniques. The powders treated at 500°C were analyzed by EDS local probe associated with HRTEM to directly detect surface segregation of Fe ions onto SnO2 nanoparticles over a broad range of concentrations. The segregation of these ions controls the system microstructure by changing the surface energies and acting as nucleation sites for the formation of a Fe oxide phase (magnetite) at high Fe concentrations. A technologically interesting core-shell-type particle structure, with a magnetic shell and semiconductor core, was observed for the first time. The influence of the segregated Fe ions in Mössbauer spectra is also addressed as a new proposal for the interpretation of the effects of composition changes in both the bulk and at the interface of particles. In this proposal, the two observed sites in Mössbauer spectra would be independently related to bulk-substituted and surface-segregated Fe ions. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.
- Surface segregation and consequent so2 sensor response in SnO2-NiO(2005-08-09) HIDALGO, P.; CASTRO, R. H. R.; COELHO, A. V. C.; GOUVEA, D.Many studies have been carried out concerning the development of SO 2 sensors to detect and avoid its health prejudicial effects. However, there is still a lack of reliable, high-speed-response sensors that work at room temperature. In this work, the segregation of Ni in the SnO 2-NiO system is used to obtain a rapid SO2 sensor response. Segregation and its structure consequences were studied by electron dispersive spectroscopy, infrared spectroscopy, and high-resolution transmission electron microscopy in nanopowders of SnO2-NiO with different compositions prepared by a polymeric precursor method. The sensor activity of SnO2-1 mol % Ni was studied and a linear calibration curve was formed with a maximum limit response of 32 ppm SO2. © 2005 American Chemical Society.