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Microstructure evolution and microstructure/mechanical properties relationships in α+β titanium alloys

Lee, Eunha
http://rave.ohiolink.edu/etdc/view?acc_num=osu1092756139

Abstract Details

2004, Doctor of Philosophy, Ohio State University, Materials Science and Engineering.
In this study, the microstructural evolution of Timetal 550 was investigated. Timetal 550 showed two types of phase transformations (martensitic and nucleation and growth) depending on the cooling rate from the β region. The α phase initially precipitated at the prior β grain boundaries, and it had a Burgers OR with one of the adjacent grains. It was found that colonies could grow, even in the fast-cooled Timetal 550 sample, from the grain boundary α into the prior β grain with which it exhibited the Burgers OR. Three orientation relationships were also found between α laths in the basketweave microstructure. Microhardness testing demonstrated that fast-cooled Timetal 550 samples with basketweave microstructure were harder than slowly-cooled samples with colony microstructure. Orientation-dependent deformation was found in the colony microstructure. Specically, when the surface normal is perpendicular to the [0001] of α, the material deforms easily in the direction perpendicular to the [0001] of α. Fuzzy logic and Bayesian neural network models were developed to predict the room temperature tensile properties of Timetal 550. This involved the development of a database relating microstructural features to mechanical properties. A Gleeble 3800 thermal-mechanical simulator was used to develop various microstructures. Microstructural features of tensile-tested samples were quantified using stereological procedures. The quantified microstructural features and the tensile properties were used as inputs and outputs, respectively, for modeling the relationships between them. The individual influence of five microstructural features on tensile properties was determined using the established models. The microstructural features having the greatest impact on UTS and YS were the thickness of α laths and the width of grain boundary α layer, and the microstructural features having the greatest impact on elongation were the thickness of α laths and the prior β grain size. Nanoindentation testing found that the hardness of the individual grains was related to their orientations. The hardness values were highest near the [0001] stress axis, and they decreased as the stress axis deviated from [0001] orientation. Dislocation analyses indicated that the deformation in individual grains conformed to the Schmid factor analysis where slip primarily occurs on those slip systems where RSS (SF) values are highest.
Hamish Fraser (Advisor)
253 p.
Engineering, Materials Science
Timetal 550; Ti-6Al-4V; microstructure evolution; modeling microstructure/tensile properties relatioships; nanoindentation

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Citations

  • Lee, E. (2004). Microstructure evolution and microstructure/mechanical properties relationships in α+β titanium alloys [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1092756139

    APA Style (7th edition)

  • Lee, Eunha. Microstructure evolution and microstructure/mechanical properties relationships in α+β titanium alloys. 2004. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1092756139.

    MLA Style (8th edition)

  • Lee, Eunha. "Microstructure evolution and microstructure/mechanical properties relationships in α+β titanium alloys." Doctoral dissertation, Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=osu1092756139

    Chicago Manual of Style (17th edition)

osu1092756139
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© 2004, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.