Artigos
URI permanente para esta coleçãohttps://repositorio.fei.edu.br/handle/FEI/795
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Resultados da Pesquisa
- Mean strain influence in low cycle fatigue behavior of AA7175-T1 aluminum alloy(2007) Salerno G.; Magnabosco R.; Moura Neto C.d.This work evaluates the mean strain influence on total number of cycles to fatigue failure of AA7175-T1 aluminum alloy, based on empirical relationships developed by SWT, Morrow and Walker, that were used to adjust the experimental data and predict the fatigue-life behavior at different mean strain values applied during cyclic loading. It is found that Walker or SWT relationships can be used to determine the number of cycles for failure of the AA 7175-T1 aluminum alloy. The easiest determination of SWT relationship (which uses parameters found in fatigue tests at zero mean stress and strain) probably will make this relationship the first choice to characterize the fatigue behavior under non-zero mean strain. However, Walker empirical relationship uses different parameters to predict fatigue-life behavior, and this may lead to a better fit of experimental data of different metallic materials. © 2006 Elsevier Ltd. All rights reserved.
- 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.
- Kinetics of sigma phase formation in a duplex stainless steel(2009) Magnabosco R.This work determines the kinetics of sigma phase formation in UNS S31803 Duplex Stainless Steel (DSS), describing the phase transformations that occur in isothermal aging between 700 and 900 °C for time periods up to 1032 hours, allowing the determination of the Time-Temperature-Precipitation (TTP) diagram for sigma phase and proposing a model to predict the kinetics of sigma phase formation using a Johnson-Mehl-Avrami (JMA) type expression. The higher kinetics of sigma phase formation occurs at 850 °C. However, isothermal aging between 700 and 900 °C for time periods up to 1032 hours are not sufficient to the establishment of thermodynamic equilibrium. Activation energy for both nucleation and growth of sigma phase is determined (185 kJ.mol-1) and its value is equivalent to the activation energy for Cr diffusion in ferrite, indicating that diffusion of Cr is probably the major thermally activated process involved in sigma phase formation. The determined JMA type expression presents good fit with experimental data between 700 and 850 °C.
- Effect of rolling on the residual stresses and magnetic properties of a 0.5% Si electrical steel(2008) de Campos M.F.; Sablik M.J.; Landgraf F.J.G.; Hirsch T.K.; Machado R.; Magnabosco R.; Gutierrez C.J.; Bandyopadhyay A.Cold-rolled (0-19% of reduction) 0.5% Si electrical steel sheets were studied in detail, including macro and micro residual stress measurements, crystallographic texture, dc-hysteresis curves and iron losses. Even for the smallest deformation, losses increase significantly, with large increase of the hysteresis losses, whereas the anomalous losses reduce slightly. The residual microstresses are ∼150-350 MPa, whereas residual macrostresses are compressive, ∼50 MPa. The large increase of the hysteresis losses is attributed to the residual microstresses. The dislocation density estimated by X-ray diffraction is in reasonable agreement with that predicted from the Sablik et al. model for effect of plastic deformation on hysteresis. The intensity of the texture fibers {1 1 1} 〈u v w〉 and 〈1 1 0〉//RD (RD=rolling direction) increases with the reduction. © 2008 Elsevier B.V. All rights reserved.
- 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 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.
- Selective corrosion in sodium chloride aqueous solution of cupronickel alloys with aluminum and iron additions(2007) Liberto R.C.N.; Magnabosco R.; Alonso-Falleiros N.Cupronickel pipes are widely used in cooling systems. Under this application, localized corrosion is observed, particularly associated with selective corrosion of nickel (denickelification). This work studied the denickelification process in solution-treated cupronickel alloys 90-10 (Cu-10wt%Ni), with aluminum and iron additions, in 0.01 M, 0.1 M, or 0.6 M sodium chloride (NaCl) aqueous solutions. Polished surfaces of the studied materials were submitted to potentiodynamic polarization, and after that, the polarized surfaces were studied using optical microscopy (OM) and scanning electron microscopy (SEM) assisted by energy-dispersive spectroscopy (EDS). A passivity break potential (Epb) was determined in all solutions, related to the initiation of selective corrosion of nickel. When submitted to cyclic potentiodynamic polarization, alloys with higher Epb showed the higher nickel losses in localized spots. However, potentiodynamic polarization tests conducted in 0.01 M NaCl until current densities of 10-1 A/cm2 were reached showed that the selective corrosion process was stopped by the formation of copper-rich corrosion products over the surface. © 2007, NACE International.
- 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.