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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.- 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.
- Effect of aging heat treatment H950 and H1000 on mechanical and pitting corrosion properties of uns s46500 stainless steel(2018-01-05) BERALDO, C. H.; CALDERON-HERNANDEZ, J. W.; Rodrigo Magnabosco; ALONSO-FALLEIROS, N.© 2018 Universidade Federal de Sao Carlos. All rights reserved.The effect of aging temperature on mechanical and pitting corrosion properties of UNS S46500 was investigated. Tensile and Hardness tests were carried out and the microstructure was analyzed by optical microscopy, scanning electron microscopy and X-ray diffraction; Thermo-Calc simulations helped in the phase identification. Pitting corrosion properties were investigated in 0.6M NaCl electrolyte with sulfate additions by Potentiodynamic Polarization (PP). Hardness, tensile and yield strength of the UNS S46500 steel after lower aging temperature, 510ºC (H950), are higher than the ones found in the 538ºC (H1000) aged steel.This result is explained by microstructure, X-ray diffraction and Thermo-Calc analysis, which indicated the presence of austenite, chi phase and probably Ni3Ti precipitates finely and uniform distributed throughout the martensite matrix. Pitting corrosion resistance is equivalent in both aging temperatures. The sulfate inhibitor effect on UNS S46500 steel was enhanced for 538ºC condition when the electrolyte reaches 1Cl-:1SO4 2- ratio, which is explained by Ni sulfate adsorption and the amount of interfaces in the microstructure resulting in smaller amount of adsorption sites, such as coarsened Ni3Ti precipitates, smaller fraction of chi phase and recovery of dislocations in martensite structure.
- 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.