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Microstructure/Composition Evolution and Ductility Variation in Thermally Aged Aluminized CoCrAlY Coatings FREE

[+] Author Affiliations
J. Kameda, T. E. Bloomer

Iowa State University, Ames, IA

Y. Sugita, A. Ito

Chubu Electric Power Co., Inc., Nagoya, Japan

S. Sakurai

Hitachi Ltd., Hitachi, Japan

Paper No. 98-GT-526, pp. V005T12A015; 7 pages
doi:10.1115/98-GT-526
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 effect of thermal ageing at 870 °C for 8000 h in air on the microstructure/composition and mechanical properties (RT and 870 °C) has been studied in aluminized CoCrAlY coatings consisting of four layered structure (region I-IV) of advanced gas turbine blades. Thermal ageing led to a little oxidation/nitridation and a decrease in the Al content in a near surface region I. In a coating region II, coarse Cr rich σ precipitates formed during the thermal ageing. Thermally aged internal (III) and near interface (IV) coating regions showed extensive dispersion of σ and/or Al/Ni rich β/α eutectic precipitates. Small punch tests at RT and 870 °C in air have shown that the coating regions I and II of imaged and aged blades indicated easier formation of brittle cracks regardless of the composition change. The ductility of the regions III and IV at RT and 870 °C, and the low cycle fatigue life of the region III were reduced by the thermal ageing. The mechanical degradation at elevated temperatures in the aged coating regions III and IV is elucidated by taking into account the microstructure/composition evolution and environmental oxidizing effects.

Copyright © 1998 by ASME
Topics: Coatings , Ductility
This article is only available in the PDF format.

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