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Effect of Mo on corrosion behavior of Ni20Cr– x Mo alloys in air with NaCl–KCl–CaCl 2 vapor at 570°C
Author(s) -
Izzuddin Hubby,
Hayashi Shigenari,
Yoneda Suzue,
Kogin Takashi,
Ishikawa Eiji,
Noguchi Manabu
Publication year - 2020
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.201911469
Subject(s) - oxidizing agent , potassium chromate , corrosion , chlorine , chromate conversion coating , chromium , non blocking i/o , alloy , salt (chemistry) , inorganic chemistry , high temperature corrosion , chemistry , water vapor , chloride , potassium , materials science , metallurgy , catalysis , biochemistry , organic chemistry
The effect of Mo on the corrosion behavior of Ni20Cr– x Mo alloys in an oxidizing chlorine‐containing atmosphere using air mixed with the salt‐vapor mixture of NaCl–KCl–CaCl 2 at 570°C was investigated. The results revealed that the corrosion performance of the Ni20Cr alloys in the oxidizing chlorine atmosphere was improved by Mo addition of up to 3 wt%. The Mo‐free alloy formed a potassium chromate during corrosion as a result of the reaction between the Cr 2 O 3 scale and KCl vapor. The chromate formation increased the chlorine potential at the scale surface and induced the breakdown of the protective Cr 2 O 3 scale, resulting in internal chromium chloride precipitates and a Cr‐depleted zone. In contrast, the presence of Mo resulted in the formation of a NiO scale, which did not react with the salt vapors and, therefore, prevented the formation of chromates. The beneficial effect of Mo on the high‐temperature chlorination of Ni–Cr alloys in salt‐vapor‐containing atmospheres was ascribed to the suppression of chlorine generation due to NiO scale formation.