Observation on void formed in oxide scale of Fe-Cr-Ni alloy at 1073K in dry and humid environments
Void formation in oxide scale during high temperature oxidation is a common phenomenon. Over a long period of time voids will affect the mechanical property of scales by influencing the cracking and spalling. Voids formed in dry environment are different than that of formed in humid environment....
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
IIUM Press
2011
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| Subjects: | |
| Online Access: | http://irep.iium.edu.my/16790/ http://irep.iium.edu.my/16790/ http://irep.iium.edu.my/16790/2/235-1219-1-PB_16790.pdf |
| Summary: | Void formation in oxide scale during high temperature oxidation is a
common phenomenon. Over a long period of time voids will affect the mechanical
property of scales by influencing the cracking and spalling. Voids formed in dry
environment are different than that of formed in humid environment. With the presence
of water vapor in humid environment the formation of void will increase, thus greater
number of void compared to that in dry environment. Fe-Cr-Ni alloy samples were
exposed isothermally at 1073 K in air (P_(O_2)= 0.21atm = 2.1 x? 10 5 Pa) and humid (air +
steam) environments. XRD analysis done to all samples confirms that Fe2O3, Fe3O4,
NiCr2O4, FeCr2O4, Cr2O3 and NiO phases exist in the scale. EDX analysis done shows
varying compositions of Fe,Cr,Ni and O in outer and inner oxide scale, oxide scale/metal
interface and metal. Field emission scanning electron microscope (FE-SEM) was used to
investigate voids formed in the cross sections of the oxidized samples. Volume fraction
of voids in the oxide scale was calculated in accordance to the cross sectional area
fraction of voids in the scale. It shows that Fe-Cr-Ni alloy samples exposed in humid
environment has as high as 71% more voids than that exposed in dry environment. It is
concluded that the humid environment increased the number of void formed in the oxide
scale, thus facilitates the exfoliation of protective scale during the high temperature
oxidation. |
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