Oxidation Behavior of Mo-Si-B Alloys in Wet Air Page: 1 of 9
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Oxidation Behavior of Mo-Si-B Alloys in Wet Air
Matthew J. Kramer
Ames Laboratory, 37 Wilhelm Hall, Iowa State University, Ames, IA 50011
E-mail: firstname.lastname@example.org; Telephone: (515) 294-0276; Fax: (515) 294-4291
Andrew J. Thom
Ames Laboratory, 142 Spedding Hall, Iowa State University, Ames, IA 50011
E-mail: email@example.com; Telephone: (515) 294-4064; Fax: (515) 294-4709
Ames Laboratory, 330 Spedding Hall, Iowa State University, Ames, IA 50011
E-mail: firstname.lastname@example.org; Telephone: (515) 294-0709; Fax: (515) 294-4709
Ames Laboratory, 333 Spedding Hall, Iowa State University, Ames, IA 50011
E-mail: email@example.com; Telephone: (515) 294-0744; Fax: (515) 294-4709
Multiphase composite alloys based on the Mo-Si-B system are candidate materials for ultra-high temperature
applications. In non load-bearing uses such as thermal barrier coatings or heat exchangers in fossil fuel burners,
these materials may be ideally suited. The present work investigated the effect of water vapor on the oxidation
behavior of Mo-Si-B phase assemblages. Three alloys were studied: Alloy 1 = Mo5Si3BX (T1)- MoSi2-
MoB, Alloy 2= T1- Mo5SiB2 (T2)- Mo3Si, and Alloy 3 = Mo- T2- Mo3Si. Tests were conducted at 10000
and 1100 C in controlled atmospheres of dry air and wet air nominally containing 18, 55, and 150 Torr H20.
The initial mass loss of each alloy was approximately independent of the test temperature and moisture content
of the atmosphere. The magnitude of these initial losses varied according to the Mo content of the alloys. All
alloys formed a continuous, external silica scale that protected against further mass change after volatilization of
the initially formed MoO3. All alloys experienced a small steady state mass change, but the calculated rates
cannot be quantitatively compared due to statistical uncertainty in the individual mass measurements. Of
particular interest is that Alloy 3, which contains a significant volume fraction of Mo metal, formed a protective
scale. All alloys formed varying amounts of subscale Mo and MoO2. This implies that oxygen transport
through the external silica scale has been significantly reduced. For all alloys, water vapor accelerated the
growth of a multiphase interlayer at the silica scale/unoxidized alloy interface. This interlayer is likely composed
of fine Mo and MoO2 that is dispersed within a thin silica matrix. Alloy 3 was particularly sensitive to water
accelerated growth of this interlayer. At 1100 C, the scale thickness after 300 hours increased from about 20
m in dry air to nearly 100 m in wet air.
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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/m1/1/: accessed June 24, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.