Oxidation Behavior of Mo-Si-B Alloys in Wet Air Page: 3 of 9
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Pellets of Alloys 1, 2, and 3 were prepared from the < 15
m size fraction of the commercially procured powders. The
powder was milled in a WC impact mill, sieved to - 635
mesh (< 20 m), uniaxially pressed into pellets, and sintered
at 1800 -19000C for 2 hours in argon. The Archimedes
density of the sintered material for all alloys was greater than
95% of theoretical density. Figure 1 shows a representative
cross-sectional view of sintered material for each of the three
ALLOY COUPON OXIDATION TESTING
Sintered pellets of Alloys 1, 2, and 3 were cut into oxidation
test coupons. The nominal coupon size was 9 mm diameter
and 1 mm thick for a nominal surface area of 1 cm2. The
rough cut faces of the coupons were polished to a 1 m
alumina abrasive finish.
A horizontal tube furnace was configured for conducting
oxidation testing to 11000C to determine the effect of H20
on the oxidative behavior of the alloys. Flowing compressed
air was used as the carrier gas, and the H20 content was
controlled by bubbling the carrier gas through a temperature-
controlled water bath. The experiment was conducted in a
sealed quartz tube with sample coupons placed in alumina
combustion boats. A mass flow controller was used to
precisely control the delivery rate of the carrier gas at 75
ml/minute with the gas stream vented through an oil bubbler.
The samples were cooled to room temperature for
interrupted mass measurements after 20, 40, 60, 80, 148,
192, and 304 hours of cumulative exposure at the desired
test temperature. Table II gives the experimental test matrix.
The water content of the flowing air was estimated as the
equilibrium vapor pressure of water when heated to 200C
(18 Torr), 400C (55 Torr), and 600C (150 Torr). This is the
maximum possible water content of the air, but the actual
water content in the oxidation studies is likely smaller. The
actual water content will be later measured using a
quadrupole residual gas analyzer.
Mo3Si or T2
Figure 1: Secondary electron or backscattered
electron image of sintered samples of (A) Alloy
1 with Ti matrix, (B) Alloy 2 with
microcracked T1 grains, and (C) Alloy 3 with
Mo grains containing intragranular porosity.
Contrast of T2 and Mo3Si are nearly identical.
Small pores and/or pockets of silica are visible
as small dark circles.
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Kramer, M.; Thom, A.; Degirmen, O.; Behrani, V. & Akinc, M. Oxidation Behavior of Mo-Si-B Alloys in Wet Air, report, April 22, 2002; Iowa. (digital.library.unt.edu/ark:/67531/metadc742667/m1/3/: accessed April 25, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.