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Relationship of corrosion product films and recrystallization of 70Cu‐30Ni alloy
Author(s) -
Zhu X.,
Lei T.
Publication year - 2001
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 - 10.1002/1521-4176(200103)52:3<213::aid-maco213>3.0.co;2-j
Subject(s) - alloy , materials science , metallurgy , corrosion , scanning electron microscope , recrystallization (geology) , microstructure , intergranular corrosion , electrochemistry , composite material , electrode , chemistry , paleontology , biology
The corrosion and microstructure of 70Cu‐30Ni alloy plates and commercial tubes were investigated by processing, electrochemical technique and seawater exposure as well as optical microscopy, SEM, EDX and AES. The alloy plate with incomplete recrystallization, consisting of deformed and recrystallized grains, demonstrates loose and porous outer layers and denickelification in the inner layers for its corrosion product films, whereas the recrystallized alloy plate forms smooth and compact corrosion product films rich in nickel after immersion in seawater for 3 and 6 months. The incompletely recrystallized alloy tube keeps an active state and the recrystallized tube has a passive zone in the anodic polarization curve in 3.5% sodium chloride. Furthermore, the former shows loose and thick corrosion product films, which are of denickelification in the inner layer and contain a significant amount of seawater species in the outer layer, and on the surface of the latter are thin uniform and compact corrosion product films containing a Ni enrichment zone which becomes richer in Ni and wider with increasing immersion time. It is found that intergranular corrosion proceeds along the boundaries of deformed and recrystallized grains, and it is ascribed to electrochemical cells built for the reason of potential difference between the two kinds of grains.