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Characterization and Oxidation Damage Modelling of MCrAlY

[+] Author Affiliations
Emanuele Pietrangeli, Filippo Cappuccini

University of Perugia, Perugia, Italy

Michelangelo Bellacci

University of Florence, Florence, Italy

Federico Iozzelli, Marco Romanelli

GE Energy – Nuovo Pignone, Florence, Italy

Paper No. GT2006-90138, pp. 925-930; 6 pages
doi:10.1115/GT2006-90138
From:
  • ASME Turbo Expo 2006: Power for Land, Sea, and Air
  • Volume 4: Cycle Innovations; Electric Power; Industrial and Cogeneration; Manufacturing Materials and Metallurgy
  • Barcelona, Spain, May 8–11, 2006
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 0-7918-4239-8
  • Copyright © 2006 by ASME

abstract

Overlay coatings based on the MCrAlY alloy system (M is Ni, CO or both) are among the most important protective coating materials applied in the hottest section of gas turbine to counteract hot corrosion and high temperature oxidation. MCrAlY coatings are arranged in γ/β-phase system, where β-phase is the Al reserve for the surface oxide layer formation. Like any coating designed to resist oxidative environments at high temperatures, MCrAlYs should be capable of developing a thermodynamically stable, slow-growing and adherent surface oxide layer. In the current paper, two HVOF thermal sprayed MCrAlYs deposited on a Ni-based superalloy have been investigated in order to assess the different high temperature oxidation resistance. Isothermal oxidation tests were performed on NiCoCrAlY coating (GT33® ) and CoNiCrAlY coating (Amdry995® ) at four temperatures for thousand hours. Coating damage was evaluated by measures of outer and inner β-phase depletion, interdiffusion zone thickness and Al reduction. Both coatings have shown optimal microstructural stability but NiCoCrAlY coating, in virtue of greater Ni and Al content, proved superior high temperature oxidation resistance. A useful model for life assessment of gas turbine buckets coatings was extrapolated from microstructure evolution data.

Copyright © 2006 by ASME
Topics: Modeling , oxidation

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