Thermal expansion behavior of Mo-Si-B system intermetallics

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dc.contributor.author Zhao, Hua-liang
dc.contributor.department Materials Science and Engineering
dc.date 2020-11-22T06:55:01.000
dc.date.accessioned 2021-02-26T09:08:03Z
dc.date.available 2021-02-26T09:08:03Z
dc.date.copyright Tue Jan 01 00:00:00 UTC 2002
dc.date.issued 2002-01-01
dc.description.abstract <p>Currently, industrial, automotive, and aerospace areas have a need for structural materials that can withstand oxidizing and aggressive environments at temperatures above 1000 0C. Mo-Si-B system intermetallics have been attracting attention as promising candidate materials for such applications, especially materials containing Mo5Si3 (T1) phase. However, Mo5Si3 single crystal has significant thermal expansion anisotropy along the a and c directions with α[Subscript C]/α[Subscript a]=2.2. Calculation by C. L. Fu et al. shows that this can result in substantially high residual thermal stresses, up to 1.8 Gpa, due to thermal expansion mismatch between different grains in the polycrystalline Mo5Si3 materials. These large stresses are higher than the compression and tension strength, so they can fracture weakly bonded grain boundaries in cooling processes during fabrication, cause grain boundary cracking. Reduction of this anisotropy of thermal expansion is necessary to produce a strain-free and crack-free microstructure. In this research, high temperature X-ray diffraction using synchrotron radiation in Debeye-Scherrer transmission geometry is employed to study the thermal expansion behavior of Mo-Si-B system intermetallics. Four multi-phase materials containing T1 phase with different compositions are explored in this study. High temperature X-ray diffraction experiment using synchrotron radiation is done at Advanced Photon Source (APS) of Argonne National Laboratory and Cornell High Energy Synchrotron Source (CHESS) of Cornell University. The Rietveld refinement of diffraction pattern is performed through using General Structure Analysis System (GSAS) program. All the Mo-Si-B intermetallics in this research show approximate linear thermal expansion behavior from room temperature up to around 10000C. For the Mo rich hyperstoichimoetric T1 phase, Mo replaces Si 4a site; their thermal expansion anisotropy tends to decrease with the increasing bonding distance of the 4b Mo-Mo atoms. For the Si rich hypostoichiometric T1 phase, the T1 phase is formed by Mo vacancy at 4b site, which helps to relief the anharmonicity of thermal expansion along c-direction and tends to decrease the thermal expansion anisotropy. Third generation synchrotron radiation coupled with an area detector has been shown to be an efficient and accurate way determining the coefficient of thermal expansion of materials with complex structure.</p>
dc.format.mimetype application/pdf
dc.identifier archive/lib.dr.iastate.edu/rtd/21377/
dc.identifier.articleid 22376
dc.identifier.contextkey 20252566
dc.identifier.doi https://doi.org/10.31274/rtd-20201118-341
dc.identifier.s3bucket isulib-bepress-aws-west
dc.identifier.submissionpath rtd/21377
dc.identifier.uri https://dr.lib.iastate.edu/handle/20.500.12876/98744
dc.language.iso en
dc.source.bitstream archive/lib.dr.iastate.edu/rtd/21377/Zhao_ISU_2002_Z5497.pdf|||Fri Jan 14 22:36:54 UTC 2022
dc.subject.keywords Materials science and engineering
dc.title Thermal expansion behavior of Mo-Si-B system intermetallics
dc.type article
dc.type.genre thesis
dspace.entity.type Publication
relation.isOrgUnitOfPublication bf9f7e3e-25bd-44d3-b49c-ed98372dee5e
thesis.degree.discipline Materials Science and Engineering
thesis.degree.level thesis
thesis.degree.name Master of Science
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