Engenharia de Materiais
URI permanente desta comunidadehttps://repositorio.fei.edu.br/handle/FEI/17
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Resultados da Pesquisa
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 de evento 0 Citação(ões) na Scopus Properties of AISI M3:2 high speed steels produced by conventional casting and by powder metallurgy techniques(2007-05-13) ARAÚJO FILHO, O. O.; AMBRÓZIO FILHO. F.The aim of this study was to determine the properties of AISI M3:2 high speed steels produced by conventional metallurgy and by other powder metallurgy routes. PM Sinter 23 produced by hot isostatic pressing of gas atomized powders, M3:2 produced by axial cold compaction and vacuum sintering of green compacts obtained from water atomized powders and VWM3C manufactured by a conventional metallurgical route were investigated in this work. Specimens of Sinter 23 and VWM3C were taken in the longitudinal and transverse direction of hot forging. Transverse rupture strength (TRS) specimens of the five M3:2 high speed steels were manufactured as per the ASTM B 528-99 standard, heat treated by austenitizing and air quenched at 1140, 1160, 1180 and 1200 °C followed by triple tempering at 540, 560 and 580 °C. These specimens were fractured in three point bending tests with a bending rate of 2.5 mm/minute. TRS and hardness (Vickers and Rockwell C) of the high speed steels were determined. Scanning electron microscopy was used to study the microstructures of specimens that had undergone the different hardening treatments and the sizes of the primary carbides were measured at 1000 X on polished and etched specimens. The Quantikov image analyzing software was used to determine primary carbide distribution and at least six micrographs of the specimens in each condition were used. Correlation between TRS and size of the primary M6C and MC type carbides was found.Artigo de evento 0 Citação(ões) na Scopus Hot extrusion and characterization of an Al-Fe-VorNb-Si powder alloy prepared by high energy milling(2008-09-29) COELHO, R. E.; AMBRÓZIO FILHO, F.This paper presents the microstructural and mechanical characterization of an alloy, Al90.8- Fe6.2-(VorNb)1.0-Si2.0 (at%), prepared by high energy milling elemental powders of Al, Fe, V and Si, followed by vacuum hot pressing and hot extrusion. The powders were milled for 10 hours at 800 and 1400 rpm and the extruded bars were characterized by X ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive analysis of selected areas. The following phases were found in the extruded bars: Al8Fe2Si, Al12(Fe,V)3Si in the alloy with V and Al8Fe2Si, Al12(Fe,Nb)3Si, and AlNb2 in the alloy with Nb. Tensile tests and Vickers hardness at room temperature were carried out on the extruded bars. The bars from powders milled at 1400 rpm showed the highest strength and hardness and are similar to those obtained by rapid solidification in the alloy Al-Fe-V-Si. The improved mechanical properties of these bars could be attributed to the dispersoids in the microstructure.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.Artigo de evento 0 Citação(ões) na Scopus Pitting corrosion of UNS S41000 and UNS S42000 stainless steels(2009-09-06) BORGES, A. O.; ALONSO-FALLEIROS, N.; Rodrigo MagnaboscoThe aim of this work is to evaluate the pitting corrosion resistance, through potentiodynamic polarization tests, in two commercial martensitic stainless steels, named UNS S41000 and UNS S42000, by using four electrolytes of 0.10M Na2SO4, with different concentration of chloride: 0.01M NaCl; 0.05M NaCl; 0.10M NaCl; 0.60M NaCl (3.5%). The received samples showed a ferritic microstructure with spheroidized carbides (annealed), whereas it was observed a microstructure of tempered martensite after heat treatment. Considering the same condition - annealed or quenched and tempered - the hardness of steel UNS S42000 was always higher than steel UNS S41000. In potentiodynamic tests, the potential scan rate was defined as 1mV/s after exploratory tests which showed this parameter influence on the curve shape. From then on, it was possible to obtain polarization curves with scanning rate of 1mV/s, starting at open-circuit potential after a five minute immersion and 600 grit surface finish. The results showed that the higher chloride ion concentration, the lower the pitting potential. For a given electrolyte, pitting potential measured for annealed steel UNS S41000 is slightly higher than the same steel on quenched and tempered condition. The intense chromium carbide precipitation at the grain boundaries of former prior austenite, a phenomenon that can lead to sensitization, may be a reason for it. Through immersion tests, it was found out that pitting potential of UNS S41000, after heat treatment, is lower than corrosion potential in the electrolyte composed of (3.5% NaCl + 0.10M Na2SO4). Otherwise, steel UNS S42000 presented higher pitting potential after heat treatment. In this case, intergranular carbide precipitation was not observed and the quench and temper treatment, at first, generates a higher content of chromium in solid solution if compared with the annealing treatment, leading to a greater corrosion resistance. Pitting density and their sizes are chloride concentration dependent: the higher ion chloride concentration, the lower is pit density and the larger is pit width. According to the studied conditions, the most suitable electrolyte for pitting potential determination is composed of (0.10M NaCl + 0.10M Na2SO4). The shape of the obtained potentiodynamic polarization curves with this electrolyte allowed the identification and accurate determination of the pitting potential.- 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.