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1773030 
Journal Article 
Improvements in honeycomb abradable seals 
Potter, DJ; Chai, YW; Tatlock, GJ 
2009 
1 
Materials at High Temperatures
ISSN: 0960-3409 
26 
2 
127-135 
WOS:000268306100003 
The concept of utilising honeycomb abradable seals to
improve gas turbine engine performance has been under development for many years. Engine
operating temperatures, in the region of the seals, have been restricted to below 950 degrees C
by the reliance on a chromia scale for degradation protection. The introduction of nickel brazed
FeCrAlY based alloys within the honeycomb seal could facilitate a safe increase in operating
temperatures to over 1100 degrees C. This is aided by the formation of a more stable, alpha-
alumina scale. These Fe-20Cr-5Al-0.5Y foils, including the commercially produced variant
designated MI2100, have been designed for a service lifetime of up to 24,000 hours. However,
burner tests and isothermal oxidation tests in laboratory air at 1100 and 1200 degrees C have
shown them to fail after much shorter times. The major degradation of the foils occurs adjacent
to the brazed region and limits the lifetime of the honeycomb seal. Cross-sectional analysis in a
scanning electron microscope of seals manufactured from MI2100 foils, after oxidation testing at
1200 degrees C, has shown that voids form beneath the protecting alpha-alumina scale. In some
cases, these voids are filled with silica, with some chromia present, and may be the origin of
the subsequent degradation process. The results contrast with tests on free-standing thin foils
(100 mu m thickness) of MI2100 and other FeCrAlY alloys, where a continuous layer of chromia is
formed below the alumina outer scale, once the aluminium content of the alloy drops below a
critical composition. Although there is a small amount of silicon in MI2100, the main source of
the high level of silicon found in the honeycombs is most likely to be the brazing alloy, since
both nickel and silicon from the braze are very mobile in FeCrAlY alloys at high temperatures.
The formation and filling of voids with silica may be associated with the subsequent failure of
the protective alumina scales on these brazed alloys, and this mechanism will be developed
further in this paper. 
honeycomb abradable seals; gas turbine engine