Processing and characterization of tantalum-hafnium carbides

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dc.contributor Kung, Patrick
dc.contributor Butts, Daniel
dc.contributor Warren, Garry
dc.contributor.advisor Thompson, Gregory B. Schulz, Bradford Christopher 2017-03-01T14:39:30Z 2017-03-01T14:39:30Z 2011
dc.identifier.other u0015_0000001_0000561
dc.identifier.other Schulz_alatus_0004M_10715
dc.description Electronic Thesis or Dissertation
dc.description.abstract A series of (TaC)100-x(HfC)x specimens were manufactured by two different processing techniques and studied to determine the effect of hafnium content on the tantalum carbide microstructure. The first set of (TaC)100-x(HfC)x specimens, where X is 0.3, 3.0, 16.5, and 19.8 at.% HfC, were fabricated by the vacuum plasma spraying process (VPS) with subsequent sintering and hot isostatic pressing (HIPing) to homogenize the microstructure. The second set of specimens of (TaC)100-x(HfC)x, where X is 5.8, 10.7, 17.6, and 25.0 at.% HfC, were fabricated from arc melted powder blends (AMPP) of these compositions with subsequent hot isostatic pressing and spark plasma sintering (SPS). It was found that as HfC content increased, the grain size was reduced, the porosity fraction increased, and volume fraction of TaC, Ta2C and Ta4C3 changed. The reduction of grain size with increasing HfC content has been explained by the system being driven further into a compositionally lower melting temperature phase field upon solidification of either the powders in the VPS plasma plum or the initial state of the arc melted powders for AMPP-SPS. This increase in liquid fraction caused greater under-cooling and the formation of more nucleation sites that lead to a finer grain size. The changing volume fraction of (TaC)100-x(HfC)x and sub-stoichiometric tantalum carbide phases has been explained through the unequal loss of constituent species during processing. The addition of HfC content improved the micro hardness values as tested by Knoop indentation at room temperature. It was observed that the micro hardness values increased with respect to increasing HfC content. The addition of HfC content was found to improve the oxidation resistance at 1000oC. The oxide scale was composed primarily of orthogonal and hexagonal Ta2O5 and monoclinic HfO2 phases.
dc.format.extent 90 p.
dc.format.medium electronic
dc.format.mimetype application/pdf
dc.language English
dc.language.iso en_US
dc.publisher University of Alabama Libraries
dc.relation.ispartof The University of Alabama Electronic Theses and Dissertations
dc.relation.ispartof The University of Alabama Libraries Digital Collections
dc.relation.hasversion born digital
dc.rights All rights reserved by the author unless otherwise indicated.
dc.subject.other Materials Science
dc.title Processing and characterization of tantalum-hafnium carbides
dc.type thesis
dc.type text University of Alabama. Dept. of Metallurgical and Materials Engineering Metallurgical/Materials Engineering The University of Alabama master's M.S.

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