Engenharia de Materiais

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Interaction between precipitation, normal grain growth, and secondary recrystallisation in austenitic stainless steel containing particles
(1999) Padilha A.F.; Dutra J.C.; Randle V.
With the aid of various complementary methods of microstructural analysis, the precipitation, grain growth, and secondary recrystallisation behaviour of an 15Cr-15Ni-1.2Mo-Ti-B (wt-%) austenitic stainless steel were studied over prolonged periods of time in the temperature range 600-1300°C. The experimental results showed that several types of precipitates were present in the material, and that the dissolution temperatures of each of these correlated with the type and extent of grain growth which was observed. It was, therefore, concluded that in the present study secondary recrystallisation was caused directly by the interaction of precipitates with grain boundaries. Furthermore, secondary recrystallisation produced a strong, predominantly {122} 〈012〉 texture which has not previously been reported. © 1999 IoM Communications Ltd.
VIDA EM FADIGA DE AÇOS CARBONO COM ESTRUTURA BIFÁSICA FERRITA-MARTENSITA
(2001-10-31) Rodrigo Magnabosco; BOTTON, T.
Interaction Between Second-Phase Particle Dissolution and Abnormal Grain Growth in an Austenitic Stainless Steel
(2002) DUTRA, J. C.; SICILIANO JR, Fulvio; PADILHA, A. F.
Sintering behavior of aluminum nitride doped with Y2O3
(2003) MOLISANI, A. L.; Goldenstein, H.; Cruz, A.C. da; Bressiani, A.H.A.; DUTRA, J. C.; Manholetti, J.L.A.; Horita, G.I.; Yoshimura, H.N.
Toughness of Two HSLA Steel Sheets
(2003) Magnabosco R.; Rossetto L.C.
This paper presents a study concerning the toughness anisotropic behavior of two high-strength low-alloy steel sheets having ferrite-martensite (dual-phase) and ferrite-perlite grain-refined structures. The anisotropic behavior quantification was possible through tension and Charpy impact tests. It has been concluded that mechanical resistance has higher values in the longitudinal direction for both steels, and the inverse occurs for ductility. This could be explained with the microstructure preferential orientation with rolling direction. The higher tensile strength found in dual-phase steel is related to the presence of martensite islands, and the higher yield strength found in ferrite-perlite grain-refined steel is related to the fine structure observed. The higher toughness is a ferrite-perlite grain-refined steel characteristic, and this could be explained with the presence of only globular-oxide type inclusions, which reduces fracture nucleation sites, and does not promote fracture easy-propagation. Sulfide type inclusions found in dual-phase steel, associated with globular-oxide ones, give to this material a more brittle behavior. Toughness anisotropy is clearly noted, and in both cases the highest values are found inthe longitudinal direction, related to the preferential inclusion alignment achieved in rolling. The low ductile-to-brittle transition temperature found in both steels, however, could be related to the very fine structures found.
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.
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.
Sigma phase formation and polarization response of UNS S31803 in sulfuric acid
(2005) Magnabosco R.; Alonso-Falleiros N.
For a better understanding of the relationship between the microstructure of UNS S31803 duplex stainless steel (DSS) and the shape of the polarization curves, this study evaluated the influence of the microstructure on the potentiodynamic polarization of the 850°C isothermal-aged UNS S31803 DSS in 0.5 M sulfuric acid (H2SO4). In the transpassive region, selective corrosion of chromium- and molybdenum-rich phases occurred. In the solution-treated sample, ferrite was selectively corroded, and in all aged samples, the sigma phase was the selectively corroded phase. Five current density maxima in the passive region were found during potentiodynamic polarization, and they can be related to the microstructures formed. The current density maximum at 564 mV us. saturated calomel electrode (SCE) can be related to secondary ferrite, impoverished in chromium and molybdenum, that was formed during direct precipitation of sigma phase from the original ferrite. Secondary austenite, impoverished in chromium and molybdenum and formed together with the sigma phase during eutectoid decomposition of the original ferrite, can be related to the current density maxima at -85 mVSCE and -40 mVSCE. The austenite phase, present in all heat-treatment conditions, can be related to the current density maxima at -155 mVSCE and 111 mVSCE. © 2005, NACE International.
Pit morphology and its relation to microstructure of 850°C aged duplex stainless steel
(2005) Magnabosco R.; Alonso-Falleiros N.
The relation between pit morphology and microstructure formed during 850°C isothermal aging of UNS S31803 duplex stainless steel (DSS) could be reached through the explanation of pit nucleation and growth during potentiodynamic polarization in 3.5 wt% sodium chloride (NaCl) aqueous solution. Aging times up to 10 min at 850°C led to sigma formation by direct precipitation from ferrite, resulting in Cr- and Mo-depleted ferrite, or secondary ferrite. Between 30 min and 5 h of aging, the ferrite suffered eutectoid decomposition, resulting in sigma phase and secondary austenite, also impoverished in Cr and Mo. Those Cr- and Mo-depleted zones around the sigma phase were preferential sites for the nucleation of pits. At those sites, the passive film breakdown was easier, as shown by the low pitting potential values found in aged samples. Pit growth occurred as selective corrosion of the metallic matrix surrounding the sigma phase, as a consequence of the lower corrosion resistance of the secondary ferrite and austenite phases found. The low passivation potential values indicated the difficulty in repassivation of the pits formed, probably related to the Cr and Mo depletion of the regions surrounding the sigma phase. © 2005, NACE International.
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.
Growth and morphological characterization of Al-Cr-Nb eutectic alloys
(2005-10-27) SOUZA, S. A.; RIOS, C. T.; COELHO, A. A.; FERRANDINI, P. L.; GAMA, S.; CARAM, R.
Directional solidification of eutectic alloys attracts considerable attention, when in situ composites are concerned. The eutectic alloys are regarded as presenting regular morphology (lamellar and fibrous structures). Besides, when directionally solidified they show high microstructure stability at high temperatures. This work reports a morphological study of an Al-Cr-Nb eutectic alloy. The solidification morphology of the alloys was studied both in the as-cast and in the directionally solidified conditions. The samples were first obtained in an arc furnace and then directionally solidified using Bridgman equipment. During the directional solidification process, the growth rates utilized varied from 5.0 to 30.0 mm/h. Optical (OM) and scanning electron microscopy (SEM) was used in order to determine the influence of the solidification conditions on the microstructure. The results obtained indicated that the eutectic transformation temperature is near 1347.9 °C with formation of Al3(Nb,Cr) and Cr(Al,Nb) phases. Also, it was noted that the Cr(Al,Nb) phase undergoes a polymorphic transformation (∼892.3 °C) forming the Al(Nb)Cr2 compound, followed by eutectoid decomposition Cr(Al,Nb) → Al(Nb)Cr2 + Al8Cr5. © 2005 Elsevier B.V. All rights reserved.
A new method for obtaining adsorption isotherms on colloidal suspensions via electrokinetic sonic amplitude measurement
(2005-12-06) GUIMARAES, K. L.; CASTRO, R. H. R.; GOUVEA, D.
The standard methods for obtaining adsorption isotherms on colloidal suspensions are usually very time consuming and involve a large number of steps and assumptions that increase the experimental errors. In this work, an alternative method is proposed to evaluate the adsorption behavior of electrostericstabilized systems based on electrokinetic sonic amplitude signal measurements. The new method, entitled "zeta-sorption", is noticeably less time-consuming when compared to conventional procedures but showed great precision and reliability confirmed by comparison with data obtained from conventional routes on alumina-polyacrylate and alumina-citric acid aqueous suspensions. The experimental conditions that restrict the applicability of the new method were identified and justified by discussing the possible ion exchanges. © 2005 American Chemical Society.
Fitting the flow curve of a plastically deformed silicon steel for the prediction of magnetic properties.
(2006) SABLIK, M.; LANDGRAF, F. J. G.; MAGNABOSCO, R.;Magnabosco, R.;Rodrigo Magnabosco;R. Magnabosco;R. MAGNABOSCO;Magnabosco, Rodrigo; FUKUHARA, M.; CAMPOS, M. F.; MACHADO, R.; MISSELL, F. P.
Sensitization and pitting corrosion resistance of ferritic stainless steel aged at 800°C
(2006) Paroni A.S.M.; Alonso-Falleiros N.; Magnabosco R.
This work investigates the influence of sensitization conditions on pitting corrosion resistance of ferritic stainless steel UNS S43000 aged at 800°C between 10 min and 320 min. UNS S43000 steel is susceptible to intergranular corrosion after solution treatment at 1,160°C followed by water-quenching, as a consequence of the chromium depletion of the grain boundaries adjacent areas, due to chromium carbide precipitation during cooling. Isothermal treatments of 10 min at 800°C decrease the sensitization degree, and intergranular corrosion resistance is recovered after 20 min at 800°C. The solution-treated specimens have a high pitting potential in 3.5% sodium chloride (NaCl) solution compared to the same material treated at 800°C for 10 min. The resistance to pitting corrosion is reduced by chromium depletion associated with an increase of inter- and intragranular precipitation of chromium carbide. For treatments longer than 20 min at 800°C, the pitting corrosion resistance returns to the high level observed for the solution-treated condition, as a consequence of chromium redistribution that occurs after 20 min at 800°C. The scan rate used in potentiodynamic tests plays a minor role on the pitting potential, while a rougher surface leads to lower pitting potentials in all studied conditions. © 2006, NACE International.

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