Hot Corrosion Behavior and Mechanism of High-Velocity Arc-Sprayed Ni-Cr Alloy Coatings

Abstract

High-temperature corrosion affects many components used in coal-fired power plants. A possible solution is the use of protective coatings. In this study, Ni-Cr alloy coatings with different Cr contents (30 at.%, 45 at.%, and 50 at.%) and Ni-Cr-Ti coatings were deposited on 20G boiler steels by high-velocity arc spraying. The hot corrosion behavior of the coatings was characterized in the aggressive environment of Na2SO4 + 30% K2SO4 molten salt under cyclic conditions at 750°C. x-Ray diffraction analysis, optical microscopy, and scanning electron microscopy were used to analyze the phase composition, microstructure, and corrosion products of the coatings. The corrosion kinetic curves of the coatings, established by thermogravimetry, conformed to the classic parabolic law, revealing that the Ni-Cr-Ti coatings exhibited better hot corrosion resistance than the Ni-45Cr or Ni-30Cr coatings. However, among the four tested coatings, the Ni-50Cr coating was found to offer the best protection with the lowest values of mass gain per area (2.9 mg/cm2) and parabolic rate constant (kp, 0.215 × 10−11 g2 cm−4 s−1). This can be explained by the formation of Cr2O3 and NiCr2O4. Therefore, such high-velocity arc-sprayed Ni-50Cr coatings could be used as protective layers for hot components in boiler tubes.