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Corrosion Study Of Interstitially Hardened SS 316L AND IN718 In Simulated Light Water Reactor Conditions

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2017, Doctor of Philosophy, University of Akron, Chemical Engineering.
Corrosion of structure materials in light water reactors (LWRs) can be ultimately equally disastrous as the immediate attack and degradation of components, which arise from the formation and behavior of corrosion products[1]. Especially, stress corrosion cracking (SCC) can lead to unexpected sudden failure of normally ductile construction materials in LWRs. This study presents an investigation on the corrosion properties of interstitially hardened (IH) austenitic stainless steel 316L and nickel-based Inconel 718 by low temperature carburization/nitro-carburization (IH-C/IN-NC SS 316L/IN718), which are being developed for use in light water reactors, specifically, as a surface treatment for fuel cladding to increase accident tolerance during loss-of-coolant accidents. Microstructure and chemical composition of the oxides were characterized after long-term exposure test in simulated oxidizing BWR-NWC environment. Stress corrosion cracking susceptibility was investigated via slow strain rate test with different applied strain rate. After 500 hours exposure in the simulated environment, the oxides formed on IH-C SS 316L were identified as loosely packed spinel outer layer and nano-scale Ni enriched spinel inner layer with a relatively compact Cr-rich spinel intermediate layer. The proposed oxidation mechanisms were consistent with metal dissolution/oxide precipitation and solid-state growth mechanism. Whereas, their oxidation procedure might be modified due to the high concentration near-surface interstitial carbon, which had a high affinity with Cr. Duplex oxide structures were identified on both IH-C and IH-NC IN718 samples with distinct interface between the top single crystal spinel scales and inner fine polycrystal oxides. However, Cr enriched regions were observed at the bottom of the outer scales of both IH-C and IH-NC samples. While, IH-NC IN718 exhibited the smallest weight loss and thinnest oxide layer thickness. It was found from the study of cross section that pitting corrosion occurred along the boundary of Nb carbides and substrate on all three samples. The fracture surface of IH-treated SS 316L was consistent with brittle fracture and TGSCC. A large number of brittle fracture events that penetrate through to the underlying alloy along the gauge surface was observed. In comparison, the mechanical properties and fracture surface of IH-treated IN718 were similar if not identical to the non-treated 718. To manifest the role of the interstitially hardened layer and the oxidizing environment on the stress corrosion cracking behavior, Ultrasonic Nanocrystal Surface Modification (UNSM) was employed to modify the SS 316L specimen and hydrogenated BWR environment was simulated. The findings in this study conclude that the role of the IH layer is to initiate a sharp crack which otherwise was not possible for the material. The propagation of that crack in the underlying alloy, and ultimately TGSCC failure, was dependent on the environment (solution and potential) to which it was exposed.
Scott Lillard (Advisor)
Zheng Jie (Committee Member)
Rajeev Gupta (Committee Member)
Gary Doll (Committee Member)
Curtis Clemons (Committee Member)
Gerald Young (Committee Member)
149 p.

Recommended Citations

Citations

  • Niu, W. (2017). Corrosion Study Of Interstitially Hardened SS 316L AND IN718 In Simulated Light Water Reactor Conditions [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1490998919124215

    APA Style (7th edition)

  • Niu, Wei. Corrosion Study Of Interstitially Hardened SS 316L AND IN718 In Simulated Light Water Reactor Conditions . 2017. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1490998919124215.

    MLA Style (8th edition)

  • Niu, Wei. "Corrosion Study Of Interstitially Hardened SS 316L AND IN718 In Simulated Light Water Reactor Conditions ." Doctoral dissertation, University of Akron, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1490998919124215

    Chicago Manual of Style (17th edition)