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A Multi-Scale Simulation Approach to Deformation Mechanism Prediction in Superalloys

Lv, Duchao
http://orcid.org/0000-0002-8575-6215
http://rave.ohiolink.edu/etdc/view?acc_num=osu1469009668

Abstract Details

2016, Doctor of Philosophy, Ohio State University, Materials Science and Engineering.
High-temperature alloys in general and superalloys in particular are crucial for manufacturing gas turbines for aircraft and power generators. Among the superalloy family, the Ni-based superalloys are the most frequently used due to their excellent strength-to-weight ratio. Their strength results from their ordered intermetallic phases (precipitates), which are relatively stable at elevated temperatures. The major deformation processes of Ni-based and Co-based superalloys are precipitate shearing and Orowan looping. The key to developing physics-based models of creep and yield strength of aircraft engine components is to understand the two deformation mechanisms mentioned above. Recent discoveries of novel dislocation structures and stacking-fault configurations in deformed superalloys implied that the traditional anti-phase boundary (APB)-type, yield-strength model is unable to explain the shearing mechanisms of the gamma” phase in 718-type (Ni-based) superalloys. While the onset of plastic deformation is still related to the formation of highly-energetic stacking faults, the physics-based yield strength prediction requires that the novel dislocation structure and the correct intermediate stacking-fault be considered in the mathematical expressions. In order to obtain the dependence of deformation mechanisms on a material’s chemical composition, the relationship between the generalized-stacking-fault (GSF) surface and its chemical composition must be understood. For some deformation scenarios in which one precipitate phase and one mechanism are dominant (e.g., Orowan looping), their use in industry requires a fast-acting model that can capture the features of the deformation (e.g., the volume fraction of the sheared matrix) and reduces lost time by not repeating fine-scale simulations. The objective of this thesis was to develop a multi-scale, physics-based simulation approach that can be used to optimize existing superalloys and to accelerate the design of new alloys. In particular, density functional theory (DFT) was used to calculate the GSF surface of the gamma” phase in the 718-type superalloy. In addition, the deformation pathways inside the gamma” particles were identified, and the dislocation emissions were predicted. Many novel dislocation sources inside the gamma” particles were simulated by using the phase-field method, which predicts and explains the dislocation configurations that appear during the deformation process or that are left as debris. Moreover, based on the stacking-fault energies in the available literature, we calculated the dependence of the chemical composition of the GSF surface of the gamma’ phase in Co-based, CoNi-based, and Ni-based superalloys. The phase-field simulation, which used the GSF surfaces as inputs, explained the relationship between the shearing mechanism and chemical composition. Thus, two fast-acting models were developed by using the modified analytic expressions of particle shearing and Orowan looping. These expressions were calibrated by using the GSF surface and the simulation of the phase-field, and they were used to predict the yield strength of 718-type superalloy and the localized creep features of the gamma/gamma’ microstructure. The fast-acting yield models were trained by the available experimental results. Since the chemical re-ordering and the segregation effects are not considered in this work, the fast-acting models are designed to the predict mechanical behaviors at the room temperature and the intermediate temperature.
Yunzhi Wang (Advisor)
Michael Mills (Committee Member)
Stephen Niezgoda (Committee Member)
248 p.
Materials Science
precipitation hardening; stacking fault ribbon; dislocation creep; yield strength; ab initio calculation; phase field simulation

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Citations

  • Lv, D. (2016). A Multi-Scale Simulation Approach to Deformation Mechanism Prediction in Superalloys [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1469009668

    APA Style (7th edition)

  • Lv, Duchao. A Multi-Scale Simulation Approach to Deformation Mechanism Prediction in Superalloys. 2016. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1469009668.

    MLA Style (8th edition)

  • Lv, Duchao. "A Multi-Scale Simulation Approach to Deformation Mechanism Prediction in Superalloys." Doctoral dissertation, Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1469009668

    Chicago Manual of Style (17th edition)

osu1469009668
585
© 2016, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.