Defect Structures in Ordered Intermetallics; Grain Boundaries and Surfaces in FeAl, NiAl, CoAl and TiAl

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dc.contributor.authorMutasa, Batsirai M.en
dc.contributor.committeechairFarkas, Dianaen
dc.contributor.committeememberKampe, Stephen L.en
dc.contributor.committeememberKriz, Ronald D.en
dc.contributor.committeememberAning, Alexander O.en
dc.contributor.committeememberMishin, Yuri M.en
dc.contributor.committeememberReynolds, William T. Jr.en
dc.contributor.departmentMaterials Science and Engineeringen
dc.date.accessioned2014-03-14T20:21:33Zen
dc.date.adate1997-05-16en
dc.date.available2014-03-14T20:21:33Zen
dc.date.issued1997-05-16en
dc.date.rdate1997-05-16en
dc.date.sdate1998-07-19en
dc.description.abstractOrdered intermetallics based on transition metal aluminides have been proposed as structural materials for advanced aerospace applications. The development of these materials, which have the advantages of low density and high operating temperatures, have been focused on the aluminides of titanium, nickel and iron. Though these materials exhibit attractive properties at elevated temperatures, their utilization is limited due to their propensity for low temperature fracture and susceptibility to decreased ductility due to environmental effects. A major embrittlement mechanism at ambient temperatures in these aluminides has been by the loss of cohesive strength at the interfaces (intergranular failure). This study focuses on this mechanism of failure, by undertaking a systematic study of the energies and structures of specific grain boundaries in some of these compounds. The relaxed atomistic grain boundary structures in B2 aluminides, FeAl, NiAl and CoAl and <I>L</I>1₀ γ-TiAl were investigated using molecular statics and embedded atom potentials in order to explore general trends for a series of B2 compounds as well as TiAl. The potentials used correctly predict the proper mechanism of compositional disorder of these compounds. Using these potentials, point defects, free surface energies and various grain boundary structures of similar energies in three B2 compounds, FeAl, NiAl and CoAl were studied. These B2 alloys exhibited increasing anti-phase boundary energies respectively. The misorientations chosen for detailed study correspond to the Σ5(310) and Σ5(210) boundaries. These boundaries were investigated with consideration given to possible variations in the local chemical composition. The effects of both boundary stoichiometry and bulk stoichiometry on grain boundary energetics were also considered. Defect energies were calculated for boundaries contained in both stoichiometric and off-stoichiometric bulk. The surface energies for these aluminides were also calculated so that trends concerning the cohesive energy of the boundaries could be studied. The implications of stoichiometry, the multiplicity of the boundary structures and possible transformations between them for grain boundary brittleness are also discussed.en
dc.description.degreePh. D.en
dc.identifier.otheretd-272172849731471en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-272172849731471/en
dc.identifier.urihttp://hdl.handle.net/10919/30371en
dc.publisherVirginia Techen
dc.relation.haspartmutasa.pdfen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectNiAlen
dc.subjectCoAlen
dc.subjectFeAlen
dc.subjectgrain boundariesen
dc.subjectsurfacesen
dc.subjectpoint defectsen
dc.subjectintermetallicsen
dc.subjectductilityen
dc.subjectatomistic simulationsen
dc.subjectTiAlen
dc.titleDefect Structures in Ordered Intermetallics; Grain Boundaries and Surfaces in FeAl, NiAl, CoAl and TiAlen
dc.typeDissertationen
thesis.degree.disciplineMaterials Science and Engineeringen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.leveldoctoralen
thesis.degree.namePh. D.en

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