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The influence of zirconium on the approach to steady‐state scaling in a Ni‐Cr alloy and the mechanism of inhibition of corrosion in an oxygen‐sulphur environment
Author(s) -
Strafford K. N.,
Hunt P. J.
Publication year - 1979
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.19790300603
Subject(s) - alloy , materials science , chromia , corrosion , metallurgy , ternary operation , microstructure , nucleation , non blocking i/o , intermetallic , oxide , inert gas , composite material , chemistry , biochemistry , organic chemistry , computer science , programming language , catalysis
The corrosion behaviour of a binary Ni‐15 Cr alloy and a ternary Ni‐15 Cr'1 Zr alloy has been examined when exposed to a bioxidant O 2 :SO 2 atmosphere at 850°C. The patterns of scaling exhibited by the two alloys, especially in the early stages of reaction, have been studied using optical and scanning electron microscopy and EDAX analysis. It has been established that the nucleation of Cr 2 O 3 on, and its subsequent growth over the sample surface was much more rapid with the ternary alloy than the binary material. Furthermore the steady‐state scale formed on the ternary alloy was single‐layered and contained no NiO, in contrast to the anticipated duplex‐layered scale developed on the binary material. It is suggested that the pre‐existing intermetallic network in the as‐cast microstructure of the Ni‐15 Cr‐1 Zr alloy is a key factor in promoting the rapid formation of the thin protective layer of Cr 2 O 3 , free from NiO. These features are responsible for the reduced rate of corrosion of the Zr'bearing material, relative to that exhibited by the binary alloy. The observations are discussed in the light of the published literature concerning the effects of rare earth/reactive metal and inert oxide additions to chromia‐forming alloy systems.