Improving the hot corrosion resistance of γ/γ’ in Fe-Ni superalloy coated with Cr3C2-20NiCr and NiCrAlY using HVOF thermal spray coating

In this study, the corrosion resistance of uncoated and coated Ferro Nickel-based superalloy (Fe-Ni) strengthened by the precipitation of the ordered fcc y’ Ni3(Al, Ti) was evaluated by cyclic hot corrosion testing. Fe-Ni was coated with Cr3C2-20NiCr and NiCrAlY by high-velocity oxy-fuel thermal spray coating and then tested with a mixture solution of 75 wt.% Na2SO4 + 25 wt.% NaCl at 900 °C for 50 cycles. Scanning electron microscopy combined with energy dispersive spectroscopy and X-ray diffraction were performed to investigate the corrosion products and mechanisms. The kinetics of corrosion was evaluated by measuring the mass changes. The experimental results show that the uncoated superalloy with precipitation strengthened in the substrate suffered by spallation and sputtering of the oxide scale. The presence of Cr3C2-20NiCr and NiCrAlY coating layers could significantly improve the hot corrosion resistance with the NiCrAlY layer showing a better protection performance than Cr3C2-20NiCr. A precipitation-strengthened Fe-Ni superalloy with NiCrAlY coating reduced the overall weight gain, which could be attributed to the formation of protective oxide of chromium, nickel, aluminum, and their spinel. The lower corrosion performance of the superalloy coated with Cr3C2-20NiCr layer was due to the presence of chlorine element, which increased the corrosion attack through chlorination.