Engenharia de Materiais
URI permanente desta comunidadehttps://repositorio.fei.edu.br/handle/FEI/17
Navegar
2 resultados
Resultados da Pesquisa
- Influence of sigma phase formation on pitting corrosion of an aged uns s31803 duplex stainless steel(2013) Dos Santos D.C.; Magnabosco R.; De Moura-Neto C.The main purpose of this contribution was the study of the relation between sigma formation and pitting corrosion resistance of a UNS S31803 duplex stainless steel aged at 850°C. Solution-treated samples were isothermally aged at 850°C for up to 360 h. The corrosion resistance of aged UNS S31803 steel was analyzed through cyclic potentiodynamic polarization tests in 0.6 M sodium chloride (NaCl) solution. The main mechanism of sigma phase formation was nucleation and growth from ferrite, in agreement to the Johnson-Mehl-Avrami- Kolmogorov kinetics model. This model suggests a change on the mechanisms of sigma phase formation from nucleation and growth from ferrite to the growth from austenite. Pitting morphology was related to the material microstructure. The pitting growth mechanism occurred by selective corrosion of the chromium-depleted areas of the specimens. Both pitting and repassivation potentials decreased with an increase of sigma volume fraction. Recovery of the corrosion resistance was observed in the early stages of sigma formation, probably related to chromium redistribution to depleted areas. © 2013, 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.