Development and Characterization of High-Velocity Flame Sprayed Ni/TiO2/Al2O3 Coatings on Hydro Turbine Steel

Nickel-based coatings deposited by high-velocity flame spray (HVFS) process have been widely used to overcome the slurry erosion in a hydro turbine, where many turbine components are subjected to severe erosion failure. In this work, new kind of multi-dimensional Ni-40TiO(2) and Ni-20TiO(2)-20Al(2)O(3) coatings consisting of nanostructured and micron-sized particles of TiO2 and Al2O3 were developed by HVFS process on CA6NM(13Cr4Ni) turbine steel. The in-depth characterization of the synthesized nanostructured powders, prepared coating compositions and the deposited coating was done through dynamic light scattering, scanning electron microscopy, energy-dispersive spectroscopy and x-ray diffraction techniques. The mechanical and microstructural properties of the as-sprayed specimens were evaluated and discussed in this paper. The results showed that the multi-dimensional Ni-40TiO(2) coating possessed lower porosity (0.8-2.0%), higher avg. microhardness (605 +/- 37 HV0.1), and better bond strength (66.4 MPa) than the Ni-20TiO(2)-20Al(2)O(3) coating.