Hot corrosion behaviour of HVOF-sprayed Cr3C2-NiCrMoNbAl coating

- Cr3C2-NiCrMoNbAl HVOF spray-grade powder was prepared by an agglomeration and sintering process.
- Cr3C2-NiCrMoNbAl coating was successfully deposited by HVOF spraying process.
- The coating has excellent hot corrosion resistance under chloride salts and cyclic conditions.

A novel Cr3C2-based sprayed powder consisting of hard phase (Cr3C2) and matrix phase (NiCrMoNbAl) was tailored to meet the harsh environment (corrosion, wear, high temperature) in power plant boilers. Cr3C2-NiCrMoNbAl coating was deposited by high velocity oxygen fuel (HVOF) process using the agglomerated and sintered Cr3C2-NiCrMoNbAl powder with particle size of − 45 + 15 μm. Hot corrosion test under cyclic conditions was performed in NaCl-KCl-Na2SO4 salt environment up to 650 °C. The corrosion tests were also performed for P91 steel and commercial Cr3C2-25(NiCr) coating for comparison and the corrosion loss was evaluated by measuring the coating thickness variation before and after hot corrosion test. The properties of specimens were characterized by optical microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS). The results have shown that the Cr3C2-NiCrMoNbAl-coating was deposited by HVOF spraying process with comparatively high deposition efficiency (56.6%) and low porosity (1.2%) compared to commercial Cr3C2-25(NiCr) coating. The Cr3C2-NiCrMoNbAl coating has excellent corrosion resistance compared with P91 steel and Cr3C2-25(NiCr) coating at 650 °C. The thickness loss due to corrosion is just 5% of that of P91 steel and just about 33% of that of the Cr3C2-25(NiCr) coating respectively. The hot corrosion resistance imparted by Cr3C2-NiCrMoNbAl coating may be attributed to the formation of alloy phases during the powder and coating manufacturing process and oxide formation of chromium, nickel, niobium, molybdenum and aluminium and spinels of nickel and chromium.