Slurry jet erosion performance of high-velocity flame-sprayed nano mixed Ni-40Al 2 O 3 coating in aggressive environment

Hydro turbine components are subjected to severe erosion especially during the rainy season in the Himalayan region. To protect the CA6NM turbine steel, an attempt has been made to develop the Ni-40Al₂O₃ composite coating using a high-velocity flame spray process. To lower the porosity, the coating was developed by mixing two different sizes (viz. micron and nano) of alumina (Al₂O₃) reinforcement with 60 wt.% Ni as the base powder. The characterization of the as-sprayed coating was done by scanning electron microscopy/energy dispersive X-ray spectroscopy, and PANalytical X-ray diffraction technique, whereas mechanical characterization was done for the evaluation of microhardness, bond strength, and surface roughness. The performance of the developed coating was compared with uncoated steel on slurry jet erosion test rig under accelerated conditions by varying the three parameters, viz. slurry concentration, erodent size, and impact velocity. Ni-40Al₂O₃ coating was found to be effective for minimizing the erosion rate in comparison with the uncoated steel. Scanning electron microscopy of eroded coatings mainly reveals the brittle type of signature on the coating.