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Yi Li v6.3 final.pdf (7.71 MB)

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Oxidation Behavior and Thermal Conductivity of Thermoelectric SnSe as well as Laser Powder Bed Fusion Process Modeling and Validation through In-situ Monitoring and Ex-situ Characterization

Li, Yi
http://orcid.org/0000-0003-4589-8371
http://rave.ohiolink.edu/etdc/view?acc_num=osu1546557433304004

Abstract Details

2019, Doctor of Philosophy, Ohio State University, Materials Science and Engineering.
Thermoelectric materials have drawn wide attention for decades because of their ability of converting between electricity and heat, making them one of the attractive solutions to the world-wide energy and environment challenges. A 2014 Nature article reported SnSe to exhibit an unprecedented thermoelectric performance at 600-700 °C. Oxidation and sublimation are of significant concern at such temperatures. The first part of this study investigates the oxidation behavior of SnSe between 600 °C and 700 °C in atmospheric air by monitoring its weight change. The oxidized samples are then characterized using optical microscopy, SEM, EDS, and powder XRD. Constituents of oxidation and resultant microstructure after oxidation are examined. Severity of oxidation and sublimation are discussed and a suggestion for mitigation is provided. SnSe’s ultrahigh ZT is attributed to its extra low thermal conductivity property, but there has been a significant discrepancy of its thermal conductivity values between experimental measurements and computational observations, as well as among experimental values reported by various groups. The second part of this study employed a high-throughput thermal conductivity measurement approach which is capable of measuring orientation-dependent thermal conductivities accurately at a micrometer scale. By integrating time-domain thermoreflectance (TDTR) with electron backscatter diffraction (EBSD) orientation measurement, a list of orientation-dependent thermal conductivities is obtained from polycrystalline SnSe. Three principal thermal conductivities, which were only attainable on single crystals previously, are obtained. This approach demonstrates a novel methodology to acquire principal thermal conductivities reliably without the necessity of growing single crystals. A comparison with experimentally measured values reported in the literature including the original Nature data is presented. The last part of this study aims to understand laser-powder bed fusion (L-PBF) additive manufacturing (AM) process through modeling and validating the models by in-situ monitoring as well as ex-situ characterization. A meso-scale 3D transient model, which is capable of capturing individual particle and laser interaction, is utilized to simulate heat transfer and fluid flow of the molten pool. A discrete element method is used to calculate the arrangement of particles on both flat and non-flat substrates whose surface topology information is acquired from a profilometer. Experimentally, single linear tracks with low and high heat inputs are deposited by L-PBF using AISI 316L powder. High-speed video and two-wavelength infrared camera are utilized to capture the temperature profile around the laser beam and the molten pool morphology during fusion. Comparisons between modelling results, longitudinal/transverse cross sections and in-situ monitoring data are made and discussed. This study addresses the lack of experimental validation and in-situ monitoring of AM process models. The new methodology could be a potential subroutine for development and validation of future simulation tools before implementing in industry.
Ji-Cheng Zhao (Advisor)
Wolfgang Windl (Committee Member)
Glenn Daehn (Committee Member)
257 p.
Materials Science
Thermoelectric materials; SnSe; Oxidation behavior; Ultra-low thermal conductivity; Time-domain thermoreflectance; EBSD; Additive manufacturing; Laser-powder bed fusion; Discrete element method; Single tracks; Balling defects

Recommended Citations

Citations

  • Li, Y. (2019). Oxidation Behavior and Thermal Conductivity of Thermoelectric SnSe as well as Laser Powder Bed Fusion Process Modeling and Validation through In-situ Monitoring and Ex-situ Characterization [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1546557433304004

    APA Style (7th edition)

  • Li, Yi. Oxidation Behavior and Thermal Conductivity of Thermoelectric SnSe as well as Laser Powder Bed Fusion Process Modeling and Validation through In-situ Monitoring and Ex-situ Characterization. 2019. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1546557433304004.

    MLA Style (8th edition)

  • Li, Yi. "Oxidation Behavior and Thermal Conductivity of Thermoelectric SnSe as well as Laser Powder Bed Fusion Process Modeling and Validation through In-situ Monitoring and Ex-situ Characterization." Doctoral dissertation, Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1546557433304004

    Chicago Manual of Style (17th edition)

osu1546557433304004
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This open access ETD is published by The Ohio State University and OhioLINK.