Hot corrosion behavior of detonation gun sprayed Cr_3C_2-NiCr coatings on Ni and Fe-based superalloys in Na_2SO_4-60 percent V_2O_5 environment at 900 deg C

摘要

The present work investigates the hot corrosion resistance of detonation gun sprayed (D-gun) Cr_3C_2-NiCr coatings on Superni 75, Supemi 718 and Superfer 800 H superalloys. The deposited coatings on these superalloy substrates exhibit nearly uniform, adherent and dense microstructure with porosity less than 0.8 percent . Thermogravimetry technique is used to study the high temperature hot corrosion behavior of bare and Cr_3C_2-NiCr coated superalloys in molten salt environment (Na_2SO_4-60 percent V_2O_5) at high temperature 900 deg C for 100 cycles. The corrosion products of the detonation gun sprayed Cr_3C_2-NiCr coatings on superalloys are analyzed by using XRD, SEM, and FE-SEM/EDAX to reveal their microstructural and compositional features for elucidating the corrosion mechanisms. It is shown that the Cr_3C_2-NiCr coatings on Ni- and Fe-based superalloy substrates are found to be very effective in decreasing the corrosion rate in the given molten salt environment at 900 deg C. Particularly, the coating deposited on Superfer 800 H showed a better hot corrosion protection as compared to Superni 75 and Superni 718. The coatings serve as an effective diffusion barrier to preclude the diffusion of oxygen from the environment into the substrate superalloys. It is concluded that the hot corrosion resistance of the D-gun sprayed Cr_3C_2-NiCr coating is due to the formation of desirable microstructural features such as very low porosity, uniform fine grains, and the flat splat structures in the coating.