On the Reaction Mechanism of MCrAlY Alloys with Oxide–Sulfate Deposits at 1100 °C
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- 作者：Thomas Gheno ; Brian Gleeson
- 关键词：MCrAlY coatings ; Al2O3 scale ; Selective oxidation ; Silicate deposits
- 刊名：Oxidation of Metals
- 出版年：2016
- 出版时间：December 2016
- 年：2016
- 卷：86
- 期：5-6
- 页码：385-406
- 全文大小：5,487 KB
- 刊物类别：Chemistry and Materials Science
- 刊物主题：Chemistry
Inorganic Chemistry
Tribology, Corrosion and Coatings
Metallic Materials - 出版者：Springer Netherlands
- ISSN：1573-4889
- 卷排序：86
文摘
The corrosion of γ-(Ni,Co) + β-(Ni,Co)Al NiCoCrAlY alloys exposed to CaO-rich, Na2SO4-containing deposits in air and CO2–H2O–O2 at 1100 °C was studied with a focus on the mechanisms governing the accelerated attack of γ-rich compositions. Internal oxidation of Al resulted from the breakdown of an initially formed Al2O3 scale, due to its reaction with the deposit. Compared to deposit-free conditions, this scale exhibited: (i) a delayed Al2O3 structure transition from metastable θ to stable α; (ii) finer grains; (iii) a reduced adherence to the metal, to the extent that a gap developed at the metal/oxide interface; and (iv) significant permeability to S, as well as N during air exposures. The occurrence of sulfidation in S-free gases reflected the establishment of an elevated S activity under the molten Na2SO4, due to the locally reduced \(p_{{{\text{O}}_{ 2} }}\). The factors affecting the Al2O3-scale microstructure were examined, as well as the associated consequences on Al consumption and on the transition to internal oxidation. The roles of alloy and gas compositions in the identified mechanisms were also discussed.