Thermal and Microstructure Modeling of Metal Deposition Processes with Application to Ti-6Al-4V

Kelly, Shawn Michael

Thermal and Microstructure Modeling of Metal Deposition Processes with Application to Ti-6Al-4V

dc.contributor.author	Kelly, Shawn Michael	en
dc.contributor.committeechair	Kampe, Stephen L.	en
dc.contributor.committeecochair	Babu, Sudarsanam Suresh	en
dc.contributor.committeemember	Reynolds, William T. Jr.	en
dc.contributor.committeemember	Aning, Alexander O.	en
dc.contributor.committeemember	David, Stan A.	en
dc.contributor.committeemember	Christodoulou, Leonitus	en
dc.contributor.department	Materials Science and Engineering	en
dc.date.accessioned	2014-03-14T20:19:11Z	en
dc.date.adate	2004-12-03	en
dc.date.available	2014-03-14T20:19:11Z	en
dc.date.issued	2004-11-12	en
dc.date.rdate	2004-12-03	en
dc.date.sdate	2004-11-24	en
dc.description.abstract	Laser 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
dc.description.degree	Ph. D.	en
dc.identifier.other	etd-11242004-211009	en
dc.identifier.sourceurl	http://scholar.lib.vt.edu/theses/available/etd-11242004-211009/	en
dc.identifier.uri	http://hdl.handle.net/10919/29731	en
dc.publisher	Virginia Tech	en
dc.relation.haspart	Figure_8_7_Morphology_Movie.mov	en
dc.relation.haspart	SM_Kelly_Dissertation_Final.pdf	en
dc.relation.haspart	Figure_6_12_Temperature_Movie.mov	en
dc.relation.haspart	Figure_4_10_Last_4_Layers_Movie.mov	en
dc.relation.haspart	Figure_8_4_Phase_Fraction_Movie.mov	en
dc.rights	In Copyright	en
dc.rights.uri	http://rightsstatements.org/vocab/InC/1.0/	en
dc.subject	microstructure model	en
dc.subject	heat treatment	en
dc.subject	ti-6al-4v	en
dc.subject	metal deposition	en
dc.subject	titanium alloy	en
dc.subject	additive manufacturing	en
dc.subject	near net shape	en
dc.subject	thermal model	en
dc.subject	rapid prototyping	en
dc.title	Thermal and Microstructure Modeling of Metal Deposition Processes with Application to Ti-6Al-4V	en
dc.type	Dissertation	en
thesis.degree.discipline	Materials Science and Engineering	en
thesis.degree.grantor	Virginia Polytechnic Institute and State University	en
thesis.degree.level	doctoral	en
thesis.degree.name	Ph. D.	en