A method of coating a substrate is provided. A metallic layer comprising at least about 8% nickel is deposited by thermal spraying on a substrate. The metallic layer has an average density greater than about 80%. A slurry layer comprising from about 10% to about 90% aluminum or alloy thereof is deposited on the metallic layer. Heating to a temperature in excess of 500° C. (932° F.) results in the formation of an intermetallic layer of NiAl. The resulting coating is particularly suited for protecting the surfaces of incinerators or other combustion chambers.