Hot corrosion behavior of HVOF-sprayed Cr3C2-WC-NiCoCrMo coating

A novel binary carbide-based sprayed powder, consisting of hard phases (Cr3C2, WC) and matrix phase (NiCoCrMo), was designed to ensure the harsh environments (corrosion, wear, and high temperature) of power plant boilers. A Cr3C2-WC-NiCoCrMo coating was deposited by high-velocity oxygen-fuel (HVOF) process using an agglomerated and sintered Cr3C2-WC-NiCoCrMo powder with a particle size of -45+15 mu m. Hot-corrosion tests were performed under cyclic conditions using a NaCl-KCI-Na2SO4 salt environment, at temperatures up to 500 degrees C. High-temperature oxidation was performed at 500 degrees C. For comparison, corrosion and oxidation tests were also performed on a commercial Cr3C2-25(NiCr) coating, and the corrosion resistance was evaluated by measuring the thickness of the corrosion scale. The properties of the specimens were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy with energy dispersive spectroscopy. The Cr3C2-WC-NiCoCrMo and Cr3C2-25(NiCr) coatings exhibited similar oxidation-resistance properties. The Cr3C2-WC-NiCoCrMo coating exhibited superior corrosion resistance to that of the Cr3C2-25(NiCr) coating. In the case of the Cr3C2-WC-NiCoCrMo coating, the thickness of the corrosion scale was approximately one-third that of the Cr3C2-25(NiCr) coating. The hot-corrosion resistance imparted by the Cr3C2-WC-NiCoCrMo coating may be attributed to the formation of alloy phases during the powder and coating manufacturing process, as well as to the formation of Cr, W, Ni, Co and Mo oxides, and Ni and Cr spinels.