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  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.
- International Gas Turbine Institute
Computational Design of Corrosion-Resistant Fe-Cr-Ni-Al Nanocoatings for Power Generation
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Chan, KS, Liang, W, Cheruvu, NS, & Gandy, DW. "Computational Design of Corrosion-Resistant Fe-Cr-Ni-Al Nanocoatings for Power Generation." Proceedings of the 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. pp. 747-757. ASME. https://doi.org/10.1115/GT2009-59111
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