High-Temperature Erosion-Corrosion Performance of High-Velocity Oxy-Fuel Sprayed Ni-20 Cr Coating in Actual Boiler Environment

Abstract

The high-velocity oxy-fuel (HVOF) spray technique was used to deposit Ni-20Cr coating on a commonly used boiler steel ASTM A213 347H. The specimens with and without coating were exposed to the super heater zone of a thermal power plant boiler at a temperature of 973 K (700°C) under cyclic conditions to ascertain their erosion-corrosion (E-C) behavior. High-temperature oxidation behavior of the specimens was also evaluated under cyclic thermal loading conditions at an elevated temperature of 1173 K (900°C). Mass change data and thickness loss were measured to formulate the kinetics of E-C/oxidation for the specimens. The exposed specimens were characterized by X-ray diffraction (XRD) and field emission-scanning electron microscopy/energy dispersive spectroscopy (FE-SEM/EDS). The uncoated steel suffered higher E-C in comparison with its coated counterpart in terms of mass loss as well as thickness loss. It was observed that overall mass loss was reduced by 31 pct and thickness loss by 44 pct after the application of the coating. The possible formation of Cr 2 O 3 phase in the coated substrate may be suggested to contribute to better E-C behavior. During air oxidation exposures, the coating was found to be intact with only marginal spallation of its oxide scales, which is an indicator of good adhesion between the coating and substrate steel. The air oxidation mass change data indicated that the coating enhanced the oxidation resistance of the steel by 85 pct.

Characterization and High-Temperature Oxidation Behavior of Cold-Sprayed Ni-20Cr and Ni-50Cr Coatings on Boiler Steels

“…Ni as the main phase for as-sprayed Ni-20Cr was also observed by Singh [23] and Singh [24] for plasma-sprayed Ni-20Cr coatings. Formation of a similar phase was observed by Kaushal et al [25] for HVOF-sprayed Ni-20Cr coating. The phases identified by XRD analysis for as-sprayed coatings are further confirmed by the surface EDS analysis.…”

“…The results are in good agreement with the findings of Longa-Nava et al [32] and Calvrin et al [33] Formation of similar phases were confirmed by Singh [23] and Singh et al [34] for oxidation studies of plasma-sprayed Ni-20Cr coatings on boiler steels and superalloys, respectively; Sidhu [35] for HVOF-sprayed Ni-20Cr coatings on superalloys; and Sidhu [36] for HVOF-sprayed Ni-20Cr coatings on boiler steels. Kaushal et al [25] also studied the oxidation behavior of HVOF-sprayed Ni-20Cr coating on 347H boiler steel and observed the formation of similar phases. Chromium has a higher affinity for oxygen than Ni and forms more stable oxide.…”

High Temperature Behavior of Cr3C2-NiCr Coatings in the Actual Coal-Fired Boiler Environment

“…The FE-SEM analysis (Figure 3(a)) from the surface also validates the presence of Fe and O on the surface of the sample, which is further confirmed by EDS analysis from the cross-section in Figure 4(a), which shows Fe in very high percentage at points 3, 4, 5, 6 and 7 of the oxide scale layer along with a sufficient amount of O, indicating the formation of iron oxide. Formation of such types of oxide has also been analyzed by Sidhu et al, [3] Prakash et al, [23] Srikanth et al, [24] Singh, [25] Bala, [26] Kaushal et al, [27] and Kaur et al [28] . The presence of Fe 2 O 3 is further confirmed by EPMA analysis (Figure 5).…”

High temperature corrosion behaviour of wire arc sprayed Fe based coatings

“…Ten micrographs of cross-sections of each coating were taken by an optical microscope to evaluate their average porosities. The Vickers microhardness of the coatings was measured along the cross-sections of the 26 6 Balance coatings via the distance from the coating/substrate interface, with a load of 100 g and an indentation time of 15 s.…”