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Stress Relaxation of MCrAlY Bond Coat Alloys as a Function of Temperature and Strain FREE

[+] Author Affiliations
A. A. Wereszczak, J. G. Hemrick, T. P. Kirkland, J. A. Haynes

Oak Ridge National Laboratory, Oak Ridge, TN

T. J. Fitzgerald, J. E. Junkin

Westinghouse Electric Corporation, Orlando, FL

Paper No. 98-GT-403, pp. V005T12A006; 7 pages
doi:10.1115/98-GT-403
From:
  • ASME 1998 International Gas Turbine and Aeroengine Congress and Exhibition
  • Volume 5: Manufacturing Materials and Metallurgy; Ceramics; Structures and Dynamics; Controls, Diagnostics and Instrumentation; Education
  • Stockholm, Sweden, June 2–5, 1998
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 978-0-7918-7866-8
  • Copyright © 1998 by ASME

abstract

The tensile stress relaxation behavior of two NiCoCrAlY bond coat alloys was examined at several temperatures between 25 and 899°C (1650°F) and at 0.1, 0.3, 0.5, and 0.8% strain. One alloy was made from Praxair’s CO211 powder and served as the reference alloy, while the other was a Westinghouse-developed, oxide-dispersion-strengthened alloy. The specimens were loaded to the desired tensile strain at a constant strain rate, and the elastic modulus, yield strength, and yield strain were determined as a function of temperature for the two alloys using the stress/strain information from this loading segment. There was not a statistically significant difference in the high temperature elastic properties between the two alloys, although the oxide-dispersion-strengthened alloy tended to exhibit larger yield strengths. The relaxation data for both alloys were reduced into a form in which instantaneous stressing rate during relaxation was examined as a function of stress and temperature using an Arrhenius power-law model. The oxide-dispersion-strengthened alloy exhibited a larger stress exponent and activation energy than the reference alloy between 677–899°C (1250–1650°F), and was generally more creep resistant. The results from this study demonstrate that bond coat relaxation should occur during engine operation. Bond coatings fabricated from the oxide-dispersion-strengthened alloy have the potential to reduce residual stresses in the TBC ceramic top coating.

Copyright © 1998 by ASME
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