High-Temperature Erosion-Corrosion Performance of High-Velocity Oxy-Fuel Sprayed Ni-20 Cr Coating in Actual Boiler Envir
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IN order to meet the challenge of the rising cost of high performance materials, surface coating techniques have recently attracted the attention of investigators worldwide. A composite system of a base material providing the necessary mechanical strength with a protective surface coating different in structure or chemical composition supplied by a surface treatment can be an optimum choice in combining materials’ properties.[1] Among the various coating techniques, high-velocity oxy-fuel (HVOF) thermal spraying is a potential technique that can be applied to deposit oxidation/corrosion resistant coatings, since it alters the surface without affecting the bulk material properties.[2–5] Coatings produced by HVOF spray have comparatively lower porosity, higher hardness, superior bond strength, and less decarburization than many of the other thermal spraying methods such as plasma spraying.[6] It was learned from the literature that nickel-chromium (Ni-Cr) alloys were used as coatings to deal with oxidation and corrosive environments at high temperatures. G. KAUSHAL, Assistant Professor, is with the RIMT–Institute of Engineering and Technology, Mandi Gobindgarh-147301, Punjab, India. H. SINGH, Assistant Professor, is with the Indian Institute of Technology Ropar, Roopnagar-140001, Punjab, India. Contact e-mail: [email protected] S. PRAKASH, Professor, is with the Indian Institute of Technology Roorkee, Roorkee-247667, Uttarakhand, India. Manuscript submitted June 7, 2010. Article published online December 16, 2010 1836—VOLUME 42A, JULY 2011
The thermal sprayed 50/50 Ni-Cr alloy is usually recommended as an erosion-corrosion (E-C) protection for boiler tubes in power generation applications. Sundarajan et al.[7] investigated the steam oxidation performance of HVOF sprayed 80Ni-20Cr and 50Ni50Cr coatings on 9Cr-1Mo steel in order to explore their use in ultra super critical boilers. The coatings were found to be useful in providing protection against the scale growth on the steel substrate. Yamada et al.[8] investigated the corrosion behavior of Ni-50 pct Cr coatings on some Ni-based alloys. The coatings were deposited by various coating techniques such as plasma and detonation gun spraying. The samples were tested for an extended period of 7 years in a waste incinerator to clarify corrosion behaviors at 773 and 873 K (500 and 600 °C). The coatings were found to be useful in reducing the corrosion rates of the alloys. High-temperature E-C behavior of Ni-Cr coatings for Cr-Mo/ stainless steels under simulated laboratory conditions was reported by many investigators;[9–14] however, information regarding the E-C performance of Ni-20Cr coatings in actual industrial conditions is only limited. Sidhu and Prakash[15] studied the E-C performance of a plasma sprayed Ni-20Cr coating in an actual boiler environment. They observed the presence of a continuous chromium-rich layer at the scale substrate interface, which was suggested to contribute to a better corrosion resistance to the Ni-20Cr coated steel. The aim of
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