The morphology of Al{sub 2}O{sub 3} scales: indicators of phase, growth mechanisms, and grain boundary segregation

Conference · Tue Dec 31 04:00:00 EST 1996

OSTI ID:459973

Pint, B A

Advanced analysis over the past decade has resulted in increased understanding of the formation, growth, and adhesion of alumina scales. It is proposed that this can now be inferred from SEM images of the AL{sub 2}O{sub 3} scale morphology. The presence of bladelike grains is an indicator of metastable alumina phases and an outward growth mechanism. Large surface ridges indicate that the scale has transformed to {alpha}-Al{sub 2}O{sub 3}. A columnar grain structure is associated with an inward growth mechanism, while an equiaxed grain structure typically forms when both Al and O diffusion is occurring. Grain boundary segregation typically results in a fine grain size at the scale-gas interface. Examples are given from Ni- and Fe-base alumina formers ({beta}-NiAl, FeCrAl, iron aluminides) to illustrate these correlations. 5 figs, 35 refs, 1 tab.

• Research Organization: Oak Ridge National Lab., TN (United States)
• Sponsoring Organization: USDOE Assistant Secretary for Fossil Energy, Washington, DC (United States); Oak Ridge Inst. for Science and Education, TN (United States)
• DOE Contract Number: AC05-96OR22464
• OSTI ID: 459973
• Report Number(s): CONF-961040--22; ON: DE97003608
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM ALLOYS
ALUMINIUM OXIDES
CHROMIUM ALLOYS
GRAIN GROWTH
IRON ALLOYS
MORPHOLOGY
NICKEL ALLOYS
SCALING