Abstract
A high chromium content nickel alloy, Tafaloy 45CT, was developed to combat corrosion in high temperature sulfurous environments. The alloy is applied by arc thermal spraying at thickness of 15–20×10 -3 in (381– 508μm) onto surfaces such as water wall tubes in black liquor recovery boilers. The coating has a bond strength of 6500 lbf in -2 (44.82 MPa) and is well matched to the thermal expansion characteristics of steels used for boiler tube construction. Analysis of the coating indicates the presence of two solid solutions of chromium in nickel and two chromium oxides. The major component of the metallic phases is the high chromium (44%) bulk material. The other components are a small portion of the coating. Coatings in service for 18 months show surface sulfur concentrations amounting to only 1%. The sulfur is effectively blocked from more penetration by combining with the chromium and the formation of a self healing chromium oxide film on the coating's surface and within the pores with access to the atmosphere. The coating remains well bonded and protective. Coatings have been in service for over four years without failing.
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