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Computational Design of Corrosion-Resistant Fe-Cr-Ni-Al Nanocoatings for Power Generation

[+] Author Affiliations
K. S. Chan, W. Liang, N. S. Cheruvu

Southwest Research Institute, San Antonio, TX

D. W. Gandy

Electric Power Research Institute, Charlotte, NC

Paper No. GT2009-59111, pp. 747-757; 11 pages
doi:10.1115/GT2009-59111
From:
  • ASME Turbo Expo 2009: Power for Land, Sea, and Air
  • Volume 4: Cycle Innovations; Industrial and Cogeneration; Manufacturing Materials and Metallurgy; Marine
  • Orlando, Florida, USA, June 8–12, 2009
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 978-0-7918-4885-2 | eISBN: 978-0-7918-3849-5
  • Copyright © 2009 by ASME

abstract

A computational approach has been undertaken to design and assess potential Fe-Cr-Ni-Al systems to produce stable nanostructured corrosion-resistant coatings that form a protective, continuous scale of alumina or chromia at elevated temperatures. Phase diagram computation was modeled using the Thermo-Calc® software and database [1, 2] to generate pseudo-ternary Fe-Cr-Ni-Al phase diagrams to help identifying compositional ranges without undesirable brittle phases. Computational modeling of the grain growth process, sintering of voids, and interface toughness determination by indentation, assessed micro-structural stability and durability of the nanocoatings fabricated by a magnetron-sputtering process. Interdiffusion of Al, Cr, and Ni was performed using the DICTRA® diffusion code [3] to maximize the long-term stability of the nanocoatings. The computational results identified a new series of Fe-Cr-Ni-Al coatings that maintain long-term stability and a fine-grained microstructure at elevated temperatures. The formation of brittle sigma phase in Fe-Cr-Ni-Al alloys is suppressed for Al contents in excess of 4 wt.%. Grain growth modeling indicated that the columnar-grained structure with a high percentage of low-angle grain boundaries is resistant to grain growth. Sintering modeling indicated that the initial relative density of as-processed magnetron-sputtered coatings could achieve full density after a short thermal exposure or heat-treatment. Interface toughness computation indicated that Fe-Cr-Ni-Al nanocoatings exhibit high interface toughness in the range of 52–366 J/m2 . Interdiffusion modeling using the DICTRA software package indicated that inward diffusion could result in substantial to moderate Al and Cr losses from the nanocoating to the substrate during long-term thermal exposures.

Copyright © 2009 by ASME

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