Steam oxidation resistance of slurry aluminum and aluminum/silicon coatings on steel for ultrasupercritical steam turbines

Abstract

Aluminum and aluminum/silicon coatings were deposited on ferritic–martensitic P92 and austenitic IN-800HT steels in a single-step process from an environmentally friendly slurry. A B2-FeAl phase formed on both the Al and the Al/Si coatings formed on P92. On IN-800HT, both Al and Al/Si grew a B2-(Fe,Ni)Al matrix. An additional ζ2-(Fe,Ni)3Al10 phase was also detected in the Al/Si coatings. The behavior of these coatings was then studied in steam at 650 °C and 1 bar for 2000 h. The uncoated P92 displayed a significant mass gain compared to the coated ones. The coatings also reduced the mass gains of the uncoated IN-800HT but to a lesser extent than in P92. The reduction in kinetics of the coated specimens was attributed to the major formation of a protective α-Al2O3 oxide.