Oxidation studies on small atom doped Ti5Si3

dc.contributor.advisor Mufit Akinc
dc.contributor.author Thom, Andrew
dc.contributor.department Materials Science and Engineering
dc.date 2018-08-23T01:17:22.000
dc.date.accessioned 2020-06-30T07:09:15Z
dc.date.available 2020-06-30T07:09:15Z
dc.date.copyright Sun Jan 01 00:00:00 UTC 1995
dc.date.issued 1995
dc.description.abstract <p>Several Ti5Si3Zx compositions (Z = B,C,N,O and 0 ≤ x ≤ 1) were arc-melted, and powder x-ray diffraction indicates the materials maintain the Mn5Si3-type structure of undoped Ti5Si3. Single crystal x-ray diffraction verifies that the ternary additions occupy the normally vacant interstitial sites in the Mn5Si3-type structure. Interstitial nitrogen and oxygen also significantly increase the density of Ti5Si3;Coefficient of thermal expansion (CTE) of Ti5Si3 was measured by the method of high temperature x-ray diffraction. CTE along the c-axis is substantially larger than along the a-axis ([alpha] a = 8.68 ± 0.14 and [alpha] c = 20.4 ± 0.4 ppm/K from 298-873 K). This contributes to severe microcracking in coarse-grained Ti5Si3 with an average grain size 10-20 [mu]m. Reducing the grain size to 1-2 [mu]m eliminates microcracking and nearly doubles hardness to 17.1 ± 0.7 GPa. CTE anisotropy for Ti5Si3C0.85 decreases ([alpha] a = 9.43 ± 0.29 and [alpha] c = 17.9 ± 0.6 ppm/K from 298-873 K);The isothermal oxidation resistance of hot isostatically pressed Ti5Si3Zx was measured from 700∘-1306∘C in flowing high purity air. The oxidation resistance of Ti5Si3 in air is adequate up to about 700∘C, but by 900∘C, substantial mass gain occurs with rapid linear oxidation kinetics;The addition of boron, carbon, and oxygen dramatically improve the oxidation resistance of Ti5Si3. Carbon-doped Ti5Si3 maintains protective behavior to about 1200∘C and forms a thin, continuous duplex scale. A continuous external rutile layer indicates that outward diffusion of titanium to the scale/gas interface is still fast enough to support formation of the continuous rutile layer. Boron and oxygen additions also improve oxidation resistance to about 1100∘C. Both materials contain thin, adherent continuous silica scales with discrete rutile particles at the scale/gas interface. At 1306∘C, protective behavior is generally lost, but Ti5Si3O0.25 maintains protective behavior with a mass gain of about 1.1 mg/cm2 after 240 hours. The extent of interstitial bonding in oxygen-containing Ti5Si3, in contrast to carbon- and boron-containing Ti5Si3, is evidently large enough to reduce outward Ti diffusion and thus suppress formation of a continuous external rutile layer. Nitrogen-bearing Ti5Si3 behaves almost identically to undoped Ti5Si3 with little improvement in oxidation resistance.</p>
dc.format.mimetype application/pdf
dc.identifier archive/lib.dr.iastate.edu/rtd/10988/
dc.identifier.articleid 11987
dc.identifier.contextkey 6430537
dc.identifier.doi https://doi.org/10.31274/rtd-180813-12655
dc.identifier.s3bucket isulib-bepress-aws-west
dc.identifier.submissionpath rtd/10988
dc.identifier.uri https://dr.lib.iastate.edu/handle/20.500.12876/64194
dc.language.iso en
dc.source.bitstream archive/lib.dr.iastate.edu/rtd/10988/r_9540948.pdf|||Fri Jan 14 18:32:14 UTC 2022
dc.subject.disciplines Materials Science and Engineering
dc.subject.keywords Materials science and engineering
dc.subject.keywords Ceramic engineering
dc.title Oxidation studies on small atom doped Ti5Si3
dc.type article
dc.type.genre dissertation
dspace.entity.type Publication
relation.isOrgUnitOfPublication bf9f7e3e-25bd-44d3-b49c-ed98372dee5e
thesis.degree.level dissertation
thesis.degree.name Doctor of Philosophy
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