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dc.contributor.authorKelly, Shawn Michaelen_US
dc.date.accessioned2014-03-14T20:19:11Z
dc.date.available2014-03-14T20:19:11Z
dc.date.issued2004-11-12en_US
dc.identifier.otheretd-11242004-211009en_US
dc.identifier.urihttp://hdl.handle.net/10919/29731
dc.description.abstractLaser metal deposition (LMD) offers a unique combination of process flexibility, time savings, and reduced cost in producing titanium alloy components. The current challenge in processing titanium alloys using LMD methods is understanding the complex microstructure evolution as a part is fabricated layer by layer. The current work focuses on the characterization, thermal, and microstructural modeling of multilayered Ti-6Al-4V deposits. A thermal model has been developed using finite difference techniques to predict the thermal history of LMD processes. A microstructure model that predicts the alpha phase fraction and morphology evolution was constructed to quantify the effect of thermal cycling on the as-deposited microstructure evolution. Alpha dissolution and growth are modeled assuming one-dimensional plate dissolution according to a parabolic rate law, and a Johnson-Mehl-Avrami-Kolmorgorov (JMAK) nucleation and growth model, respectively. Alpha morphology (colony-alpha and basketweave-alpha) evolution is tracked using a simplistic approach. Characterization of the deposit has shown that a complex microstructure evolves consisting of a two distinct regions: a transient region of undeveloped microstructure and a characteristic layer that is periodically repeated throughout the deposit. The transient region contains a fine basketweave and colony-alpha morphology. The characteristic layer contains a two phase mixture of alpha+beta, with the alpha phase exhibits regions of colony-alpha (layer band) and basketweave-alpha morphology. The different regions of microstructural contrast in the deposit are associated with thermal cycling. The thermal model results show that a heat affected zone defined by the beta transus extends approximately 3 layers into the deposit. The phase fraction model predicts the greatest variation in microstructural evolution to occur in a layer n after the deposition of layer n+3. The results of the morphology model show that increased amounts of colony-alpha form near the top of a characteristic layer. It follows that a layer band (colony-alpha region) forms as a result of heating a region of material to a peak temperature just below the beta transus, where a large amount of primary-alpha dissolves. Upon cooling, colony-alpha forms intragranularly. The coupled thermal and microstructure models offer a way to quantitatively map microstructure during LMD processing of Ti-6Al-4V.en_US
dc.publisherVirginia Techen_US
dc.relation.haspartFigure_8_7_Morphology_Movie.moven_US
dc.relation.haspartSM_Kelly_Dissertation_Final.pdfen_US
dc.relation.haspartFigure_6_12_Temperature_Movie.moven_US
dc.relation.haspartFigure_4_10_Last_4_Layers_Movie.moven_US
dc.relation.haspartFigure_8_4_Phase_Fraction_Movie.moven_US
dc.rightsI hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Virginia Tech or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report.en_US
dc.subjectmicrostructure modelen_US
dc.subjectheat treatmenten_US
dc.subjectti-6al-4ven_US
dc.subjectmetal depositionen_US
dc.subjecttitanium alloyen_US
dc.subjectadditive manufacturingen_US
dc.subjectnear net shapeen_US
dc.subjectthermal modelen_US
dc.subjectrapid prototypingen_US
dc.titleThermal and Microstructure Modeling of Metal Deposition Processes with Application to Ti-6Al-4Ven_US
dc.typeDissertationen_US
dc.contributor.departmentMaterials Science and Engineeringen_US
dc.description.degreePh. D.en_US
thesis.degree.namePh. D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen_US
thesis.degree.disciplineMaterials Science and Engineeringen_US
dc.contributor.committeechairKampe, Stephen L.en_US
dc.contributor.committeememberReynolds, William T. Jr.en_US
dc.contributor.committeememberAning, Alexander O.en_US
dc.contributor.committeememberDavid, Stan A.en_US
dc.contributor.committeememberChristodoulou, Leonitusen_US
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-11242004-211009/en_US
dc.contributor.committeecochairBabu, Sudarsanam Sureshen_US
dc.date.sdate2004-11-24en_US
dc.date.rdate2004-12-03
dc.date.adate2004-12-03en_US


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