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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.- Processing of Metal Matrix AA2124 Aluminium Alloy Composites Reinforced By Alumina And Silicon Carbide By Powder Metallurgy Techniques(2014) ALVES, S. J. F.; SOUSA, M. M. S.; ARAÚJO, E. R. DE; AMBROZIO FILHO, F.; SANTOS, M. J. DOS; ARAÚJO FILHO, O. O. DE A.© (2014) Trans Tech Publications, Switzerland.This work aims the processing of metal matrix AA2124 aluminium alloy composites reinforced by alumina (Al2O3) and silicon carbide (SiC). The composites were manufactured by powder metallurgy techniques, in a grinding using a ball mill spex type (high energy) at a ratio of balls/ powders of 10:1 and grinding time of 30 and 60 minutes using stearic acid (C18H36O2) as lubricant to each one of the samples. The fractions used in both reinforcements were 5, 10 and 15% in mass. The microstructural characterizations of AA2124 alloy powders with the reinforcements of alumina (Al2O3) and silicon carbide (SiC) powders were obtained by scanning electron microscopy (SEM) and the particles sizes and distribuition of the particle sizes in powders produced were obtained by laser diffraction, whereas the sintered characterizations were obtained by scanning electron microscopy (SEM) and mechanical characterization of the sintered tests was achieved by Vickers hardness (HV). The composites were uniaxially cold compacted (room temperature), at a pressure of 7.0 t/cm², thus forming small pellets that were sintered (at a temperature of 500 °C) in a vacuum furnace at IPEN (SP). There was observed the influence of the respective bulk fractions of reinforcement particles used in mechanical characteristics presented in the resulting composites.
- Preparation of Molybdenum High Speed Tool Steels with Addition of Niobium Carbide by Powder Metallurgy Techniques(2014-12-01) ARÁUJO FILHO, O. O. DE A.; ANTONELLO, R. T.; GONZALEZ, C. H.; URTIGA FILHO, S. L.; AMBROZIO FILHO, F.© (2014) Trans Tech Publications, Switzerland.High speed steels processed by Powder Metallurgy (PM) techniques present better mechanical properties when compared with similar steels obtained by the conventional process of cast to ingot and hot working. PM techniques produce improved microstructures with smaller and better distribution of carbides. Liquid phase sintering high speed steel seems to be a cheaper processing route in the manufacturing of tool steels if compared to the well-known and expansive hot isostatic pressing high speed steels. The introduction of niobium as alloying element began with the object of replacing elements like vanadium (V) and tungsten (W). Phase liquid sintering consists in a manufacturing technique to process high speed steels by powder metallurgy. The aim of this work of research is to process and obtain AISI M2 and M3:2 with and without the addition of niobium carbide by high energy milling, cold uniaxial compaction and vacuum sintering in the presence of a liquid phase. The powders of the AISI M2 and M3:2 were processed by high energy milling adding a small quantity of niobium carbide (6% in mass), then the powders were characterized by means of X-ray diffraction (XRD) and scanning electron Microscopy (SEM) plus energy dispersion spectroscopy (EDS) in order to evaluate the milling process. The powders of the AISI M2 and M3:2 with the addition of niobium carbide (NbC) were uniaxially cold compacted and then submitted to vacuum sintering. The sintered samples had their microstructure, porosity and carbide distribution observed and evaluated by means of Scanning Electron Microscopy (SEM) and the mechanical property of hardness was investigated by means of Vickers hardness tests. At least five samples of each steel were investigated.
- 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.
- 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.
- The influence of the milling environment on the sintered structure of a W-Cu composite(2010-10-05) COSTA, F. A.; AMBROZIO FILHO, F.; SILVA, A. G. P.; GOMES, U. U.; LIMA. S. J. G.; ACCHAR, W.This work reports an investigation about the influence of the environment of milling on the characteristics of the powders and on the structure and density of sintered samples made of these powders. Mixtures of composition W-30wt%Cu were milled for 51 hours in a high energy planetary mill in dry and wet (cyclohexane) conditions. The milled powders have composite particles. The powders were pressed and sintered at 1050°, 1150° and 1200°C under flowing hydrogen. The isothermal times were 0 minutes for the first two temperatures and 60 minutes for the latter. The samples reached around 95% of relative density. The powders were characterized by means of XRD and SEM. The sintered samples were characterized by means of SEM, optical microscopy and density measurement. © (2010) Trans Tech Publications.
- Test to characterize the machining strength property for the AISI 316L steel(2012-08-05) COPPINI, N. L.; DUTRA, J. C.; BAPTISTA, E. A.; DA SILVA, F. F. A. P.; FERREIRA, F. A. A.; COCCUMAZZO, D.This paper explores the effect of grain size on machining strength in an Fe-Cr-Ni alloy (AISI 316L). Ideal grain growth law [1], was used to obtain the activation energy level for this steel, which was 185 kJ.mol-1 [2]. The initial grain size was measured (12 μm) and considering these values, both temperature and time values needed to achieve a final grain size ten times larger than the initial one, could be calculated, which were 1200°C and 2 hours. Ternary phase diagram analysis showed that austenite was stable at this temperature. Following, samples of 200 mm length were annealed and quenched in water to prevent any formation of sigma (μ) phase. Annealed and as-received bars were then used to compare their machining strength. Results showed that the machining strength is higher in the as received condition than the one after annealing (127 μm). It may be concluded that the bigger the grain size, the lower its machining strength. It is believed that this is caused by the pile-up of dislocations on grain boundaries, since this material exhibits large plastic deformation before fracture.
- Effects of hydrogen content in nitrogen-based sintering atmosphere on microstructure and mechanical properties of Fe-0.3%C-0.1%B alloy(2014-10-05) LOBERTO, A.; DA SILVA, M. D. C. A.; AMBROZIO FILHO, F.; DE FLORIO, D. Z.; YOSHIMURA, H. N.© (2014) Trans Tech Publications, Switzerland.For the sintered materials, the mechanical properties are strongly dependent on the density of the final product. A substantial reduction of the porosity can be achieved using additives in the powder mixture which promote the formation of a liquid phase during sintering. Boron is a potential liquid phase promoter in ferrous alloys, when sintering is carried out using hydrogen or argon atmospheres. These atmospheres, however, are costly, and the use of nitrogen containing low content of hydrogen could be beneficial. In this study the effects of 10 to 50% hydrogen in nitrogen atmosphere on the microstructure and mechanical properties of a Fe-0.3%C-0.1%B alloy sintered at 1120 and 1250°C were investigated. Boron addition increased the sintered densities, but lowered the transverse rupture strength and hardness in relation to the control alloy (Fe-0.3%C). No significant differences were observed among the samples sintered in different atmospheres for each alloy. Nitrogen containing up to 50% hydrogen atmosphere is not suitable to sinter Fe-C alloy containing boron since it lowers the mechanical properties with the formation of fragile boron nitride precipitates at the grain boundaries and lower perlite fraction.
- ZnO micro and nanofibers made by electrospinning: Fabrication and characterization(2014-08-18) NONATO, R. C.; MORALES, A. R.; VIEIRA, A. V. M.; NISTA, S. V. G.; MEI, L. H. I.; BONSE, B. C.© 2014 IEEE.In this study, the best conditions to obtain Zinc Oxide (ZnO) nanofibers were studied for further development of a composite with a biopolymer for application in scaffolds. Although the electrospinning of ZnO nanofiber is already known, there are still new aspects to be explored to optimize itsproduction. In this work were prepared six different solutions of poly(vinyl alcohol) - PVA with two different molecular weight, containing ZnO precursor, i.e. Zinc Acetate, using water or a mix of water and alcohol as solvents, and tested to understand how solution characteristics influence the final morphology of the ZnO nanofibres. This paper shows promising results for production ceramic nanofibers by electrospinning since parameters as viscosity, molecular weight, concentration, conductivity and surface tension are well controlled.
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