Browsing by Author "Song, Taeseup"

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    Crack-Growth Behavior in Thermal Barrier Coatings with Cyclic Thermal Exposure
    (MDPI, 2019-06) Song, Dowon; Song, Taeseup; Paik, Ungyu; Lyu, Guanlin; Jung, Yeon-Gil; Choi, Baig-Gyu; Kim, In-Soo; Zhang, Jing; Mechanical and Energy Engineering, School of Engineering and Technology
    Crack-growth behavior in yttria-stabilized zirconia-based thermal barrier coatings (TBCs) is investigated through a cyclic thermal fatigue (CTF) test to understand TBCs’ failure mechanisms. Initial cracks were introduced on the coatings’ top surface and cross section using the micro-indentation technique. The results show that crack length in the surface-cracked TBCs grew parabolically with the number of cycles in the CTF test. Failure in the surface-cracked TBC was dependent on the initial crack length formed with different loading levels, suggesting the existence of a threshold surface crack length. For the cross section, the horizontal crack length increased in a similar manner as observed in the surface. By contrast, in the vertical direction, the crack did not grow very much with CTF testing. An analytical model is proposed to explain the experimentally-observed crack-growth behavior.
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    Crack-Resistance Behavior of an Encapsulated, Healing Agent Embedded Buffer Layer on Self-Healing Thermal Barrier Coatings
    (MDPI, 2019) Song, Dowon; Song, Taeseup; Paik, Ungyu; Lyu, Guanlin; Jung, Yeon-Gil; Choi, Baig-Gyu; Kim, In-Soo; Zhang, Jing; Mechanical and Energy Engineering, School of Engineering and Technology
    In this work, a novel thermal barrier coating (TBC) system is proposed that embeds silicon particles in coating as a crack-healing agent. The healing agent is encapsulated to avoid unintended reactions and premature oxidation. Thermal durability of the developed TBCs is evaluated through cyclic thermal fatigue and jet engine thermal shock tests. Moreover, artificial cracks are introduced into the buffer layer’s cross section using a microhardness indentation method. Then, the indented TBC specimens are subject to heat treatment to investigate their crack-resisting behavior in detail. The TBC specimens with the embedded healing agents exhibit a relatively better thermal fatigue resistance than the conventional TBCs. The encapsulated healing agent protects rapid large crack openings under thermal shock conditions. Different crack-resisting behaviors and mechanisms are proposed depending on the embedding healing agents.