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Investigation of critical issues in thermal barrier coating durability

Kim, Hyungjun
http://rave.ohiolink.edu/etdc/view?acc_num=osu1124302514

Abstract Details

2005, Doctor of Philosophy, Ohio State University, Mechanical Engineering.
To more fully understand microstructural evolution and the development of damage in thermal barrier coating (TBC) systems, thermocyclic experiments were conducted on TBC specimens with and without top coats. The degradation of a PtAl (platinum modified aluminide) bond coat and a CMSX superalloy substrate were investigated for cyclic and quasi-isothermal heating to 1200 °C. To accelerate the oxidation of the specimens, the thermally grown oxide (TGO) was removed at 10 hour intervals. Scanning electron microscopy (SEM) and instrumented indentation were employed to investigate microstructural evolution and material property changes of the bond coat. The microstructural evolution of a PtAl bond coat is strongly affected by the type of thermal exposure and the presence of TGO. The differences between cyclic and quasi-isothermal heating indicate that stresses associated with cooling and heating significantly alter microstructural evolution. Damage to TBC specimens with EB-PVD (electron beam physical vapor deposition) processed YSZ (yttria stabilized zirconia) top coats, PtAl bond coats, and René N5 superalloy substrates was assessed during thermal cycling to 1200 °C. Acoustic emission (AE) techniques were used to temporally identify damage to the TBC. For automated, continuous, and high temperature AE detection, a custom made experimental setup with either a nickel-chrome alloy wire wave guide or an alumina wave guide was used. It was found that there are four distinct regions of AE activity during the life of a TBC. Throughout the cooling cycles, images of the top coat were collected with darkfield-type lighting. These images showed how undulations developed in the top coat. In addition, digital image correlation (DIC) was used to identify regions with interfacial damage. Finally, the images were used to analyze the spallation of the top coat. Cycling of an additional specimen was interrupted periodically for analysis with profilometry and SEM. The profilometry and SEM images were used to further investigate the failure mechanisms in TBCs. The experiments and analysis performed in this dissertation work have elucidated how various failure mechanisms develop during the life of TBCs. This work has improved the scientific understanding of TBCs and could aid in the development of improved life prediction models.
Mark Walter (Advisor)
TGO; TBC; top coats; bond coat; spallation; specimens

Recommended Citations

Citations

  • Kim, H. (2005). Investigation of critical issues in thermal barrier coating durability [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1124302514

    APA Style (7th edition)

  • Kim, Hyungjun. Investigation of critical issues in thermal barrier coating durability. 2005. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1124302514.

    MLA Style (8th edition)

  • Kim, Hyungjun. "Investigation of critical issues in thermal barrier coating durability." Doctoral dissertation, Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=osu1124302514

    Chicago Manual of Style (17th edition)

osu1124302514
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© 2005, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.