Study of Molten Salt Corrosion of High Velocity Oxy-Fuel Sprayed Cermet and Nickel-Based Coatings at 900 C
T. S. SIDHU, S. PRAKASH, R. D. AGRAWAL
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIAL
Abstract
Samples of Cr3C2-NiCr cermet and NiCrBSi coatings formed by the high velocity oxy-fuel (HVOF) process on Superni 718 superalloy have been corroded in the Na2SO4-V2O5 molten salt environment at 900 C under cyclic conditions. The hot corrosion behavior of the coatings has been investigated by means of thermogravimetric analysis, X-ray diraction, scanning electron microscopy/energy dispersive spectroscopy, and electron probe microanalyzer techniques. Eorts have been made to formulate the mode of corrosion attack. Both the coatings protected the substrate superalloy Superni 718 completely. While protecting the superalloy, the Cr3C2- NiCr cermet coating partially oxidized along the splat boundaries up to the coating substrate interface, whereas only the upper part of the coating, to about 100 lm from the surface, oxidized in the case of the NiCrBSi coating. The hot corrosion resistance of both the coatings has been attributed to the formation of protective oxides of chromium/silicon at the surface and at the splat boundaries of the coatings.
Key words: upper part; Cermet; Cr NiCr; splat; molten salt environment; substrate superalloy; hot corrosion resistance
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