B. S. Covino, S. J. Bullard, S. D. Cramer, G. R. Holcomb, M. Ziomek-Moroz, US Department of Energy, Albany, OR; D. Harvey, TWI Ltd, Cambridge, United Kingdom; S. Shrestha, Keronite Plc, Cambridge, United Kingdom
Intermetallic compounds, such as iron aluminde (Fe3Al), are known to possess good corrosion properties in certain high temperature applications. Due to the brittle nature of bulk intermetallics, there is more interest in using them as coatings for critical parts in fossil fuel power plants.
Coatings of unalloyed Fe3Al (Fe-14.3Al) intermetallic powder were deposited onto F22 steel (2.25Cr-1Mo) substrates using a JP-5000 high velocity oxy-fuel (HVOF) thermal spray system. The as-sprayed coatings were examined by electron microscopy and X-ray diffraction techniques and were characterised in terms of deposit efficiency, oxygen content and adhesion.
Fe3Al-coated steel substrates were exposed to a mixed oxidizing/sulfidizing environment at 500, 600, and 700ºC for approximately seven days. The gaseous environment consisted of Bal.N2-10%CO-5%CO2-2%H2O-0.12%H2S (by volume). All samples gained mass after exposures to the environment and the mass gains were found to be inversely proportional to temperature. Representative samples exposed at each temperature were cross-sectioned and subjected to metallographic examination. Results have been presented in terms of corrosion product formation and depth of penetration. The purpose of the research presented here was to evaluate the effectiveness of HVOF sprayed Fe3Al coating in protecting steel substrates exposed to a typical fossil energy environment.
Iron aluminide (Fe-14Al) coatings were applied to F22 steel using the HVOF process. The coated steels were exposed to a mixed oxidizing/sulfidizing environment for approximately seven days at 500, 600, and 700C. Weight gains were inversely proportional to temperature.
