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but major concern with these alloys is their ability to maintain a protective oxide scale for the extended
times necessary for commercial application. After extended exposure times, these alloys
Table 1. Nominal Compositions of Available Ferritic ODS Alloys (weight percent)
Alloy Fe Cr Al Mo T1 Y203
MA 956 Bal 20.0 4.5 - 0.5 0.5
PM 2000 Bal 20.0 5.5 - 0.5 0.5
ODM 751 Bal 16.5 4.5 1.5 0.6 0.5
ODM 331 Bal 13.0 3.0 1.5 0.6 0.5
suffer increasing loss of scale through spallation, as indicated by the trend to weight losses as shown in
Fig. 1. The oxidation life of these alloys is determined by their ability to form or reform a protective
alumina scale, and can be related to the time for the aluminum content of the alloy to be depleted to
some minimum level; this, in turn, is a function of the total aluminum content of the alloy. This
dependence on total available aluminum content is illustrated by results8 from the COST-501 project
as summarized in Fig. 2, which relates the effective life of the alloy tube (represented as 'time to
breakaway') to its wall thickness.
The major factors that result in depletion of the reservoir of aluminum in the alloy are the
inherent growth rate of the oxide, a process that consumes aluminum, and the tendency for the scale to
spall, which also results in a net loss of aluminum from the alloy together with a (temporary) increase
in oxide growth rate in the area affected by spallation. When the alloy aluminum reservoir falls below
the minimum level at which an alumina layer can be reformed, less-protective oxides of the other alloy
3
0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8.00
Timemh
Figure 1. Oxidation kinetics for ODS-FeCrAI-Y 203 alloys in air at 1200*C cycled to room
temperature every 48 hr (after ref. 8).
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Wright, I. G.; McKamey, C. G. & Pint, B. A. ODS Iron Aluminides, report, July 1, 1995; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc621577/m1/3/: accessed July 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.