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Sulfidation behaviour of nickel aluminides
Author(s) -
Schramm B.,
Auer W.
Publication year - 1996
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.19960471204
Subject(s) - sulfidation , corrosion , nickel , aluminium , nial , materials science , metallurgy , high temperature corrosion , atmospheric temperature range , kinetics , intermetallic , sulfur , thermodynamics , alloy , physics , quantum mechanics
The sulfidation behaviour of four nickel aluminium alloys containing 25 to 45 at.% Al was studied over the temperature range of 750 to 950°C in a gas mixture of H 2 ‐H 2 S (0.1 to 10 vol.%). The sulfidation kinetics were determined using a continous weight gain system. The corrosion products were examined by SEM, EDX and XRD. Sulfidation in H 2 ‐H 2 S gas mixtures formed bilayered scales consisting of an outer layer of Ni 3 S 2 and an inner layer of NiAl 3,5 S 5,5 on all alloys regardless of the different aluminium contents. In H 2 ‐H 2 S gas mixtures the sulfidation kinetic generally followed the parabolic rate law for all alloys. The influence of aluminium content on corrosion rate was relatively low. The influence of low oxygen partial pressure on sulfidation was investigated in H 2 ‐H 2 S‐H 2 O mixtures. In these atmospheres the corrosion mechanism is completely different. Severe attack by rapid internal oxidation destroyed all the alloys except Ni25Al (25 at.%Al). The internal oxidation zone consisted of a mixture of γ‐Ni 3 Al and Al 2 O 3 . On the alloys containing 36 and 45 at.% Al local attack occurred, fast growing pocks were observed after an incubation period. Nickel aluminides show this corrosion phenomena only in H 2 ‐H 2 S‐H 2 O mixtures. An interruption of the H 2 S gas flow stops the running internal oxidation. In flowing H 2 ‐H 2 O atmospheres no internal oxidation was observed. These facts prove that H 2 S is necessary for starting and maintaining the internal oxidation of the nickel aluminides.