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Nondestructive Assessment of Cold Work Effects in IN718 Superalloy

Velicheti, Dheeraj
http://rave.ohiolink.edu/etdc/view?acc_num=ucin15109264804764

Abstract Details

2017, MS, University of Cincinnati, Engineering and Applied Science: Aerospace Engineering.
There is a growing need to identify and capture material-damage precursors in critical structural materials to allow accurate prediction of the evolution of microstructure and damage processes before material failure. One such damage precursor is cold work, which has to be reliably assessed to enable accurate prediction of damage processes like stress corrosion cracking (SCC) in nickel-base superalloys. In the work presented here, the sensitivity of three well known NDE techniques, ultrasonic pulse-echo, nonlinear ultrasonic technique based on non-collinear wave mixing and eddy current, and a novel NDE technique based on Hall coefficient measurements, to cold work in IN718 superalloy at different hardness levels was examined.In the case of the ultrasonic pulse-echo technique, both attenuation, and velocity in the material change with cold work. At 20 MHz, Cold work produced a drop in the longitudinal velocity that was linearly proportional to the plastic strain and increased with hardness, and plastic deformation decreased the attenuation in a way essentially independent of the hardness level. It was also found that the longitudinal velocity increases with hardness. Next, in the case of both nonlinear ultrasonic technique based on non-collinear wave mixing and eddy current technique, cold work produced an opposite effect at low and high hardness levels, i.e., both nonlinearity parameter and conductivity increased with cold work in the case of annealed IN718 but decreased in the case of fully hardened IN718. It was also found that the electric conductivity of IN718 significantly increases with hardness. Finally, measurements were conducted by combining the alternating current potential drop method with magnetic modulation to nondestructively evaluate the Hall coefficient in IN718 nickel-base superalloy, and the Hall coefficient was found to be positive, and it exhibited roughly 20% increase with hardening. Cold work in partially and fully hardened IN718 produced a drop in the measured Hall coefficient that is linear to the plastic strain levels. All the NDE techniques presented, except eddy current technique in partially hardened IN718 and Hall coefficient technique in annealed IN718, exhibited sensitivity towards the presence of cold work in IN718. The results of this study facilitate the selection of the most suitable NDE technique for the assessment of cold work in IN718 nickel-base superalloy in various applications. Also, since all the four NDE techniques are sensitive to cold work in fully hardened IN718, proper assessment of damage due to creep, fatigue and other material damage mechanisms, would entail separation of the effect of cold work from the effect of damage in the material. Hence a dual-mode NDE technique is suggested for assessing damage in materials.
Peter Nagy, Ph.D. (Committee Chair)
Gui-Rong Liu, Ph.D. (Committee Member)
Francesco Simonetti, Ph.D. (Committee Member)
122 p.
Aerospace Materials
Nondestructive evaluation; IN718; Cold work

Recommended Citations

Citations

  • Velicheti, D. (2017). Nondestructive Assessment of Cold Work Effects in IN718 Superalloy [Master's thesis, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin15109264804764

    APA Style (7th edition)

  • Velicheti, Dheeraj. Nondestructive Assessment of Cold Work Effects in IN718 Superalloy. 2017. University of Cincinnati, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin15109264804764.

    MLA Style (8th edition)

  • Velicheti, Dheeraj. "Nondestructive Assessment of Cold Work Effects in IN718 Superalloy." Master's thesis, University of Cincinnati, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin15109264804764

    Chicago Manual of Style (17th edition)

ucin15109264804764
344
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This open access ETD is published by University of Cincinnati and OhioLINK.