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Microstructural investigation of the oxide formed on TP 347H FG during long‐term steam oxidation
Author(s) -
Hansson A. N.,
Danielsen H.,
Grumsen F. B.,
Montgomery M.
Publication year - 2010
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.200905439
Subject(s) - oxide , spinel , alloy , materials science , superheater , internal oxidation , layer (electronics) , metallurgy , grain boundary , diffusion , metal , chromia , chemical engineering , microstructure , composite material , boiler (water heating) , thermodynamics , physics , engineering
The long‐term oxidation behaviour of TP347H FG in ultra supercritical steam conditions was assessed by exposing the steel in test superheater loops in a Danish coal‐fired power plant and characterising the oxide layer with reflective light and electron microscopy. Double layered oxide scales formed during steam oxidation. TEM investigations reveal that the inner oxide layer consists of particles of metallic Ni/Fe and FeCr spinel in the interior of the former alloy grains and a compact layer of FeCr spinel and Cr 2 O 3 along the former alloy grain boundaries. The morphology suggests that the inner layer grows by internal oxidation of the interior of the alloy grains. The thickness of the inner oxide layer did not change significantly with oxidation time and temperature for exposure times up to 30 000 h. Faster Cr diffusion within the fine‐grained alloy at higher temperatures is held responsible for this observation. This hypothesis is supported by kinetic data. The oxide thickness at low and high temperatures after 58 000 h exposure was higher than expected.