DEPOSITION OF Al2O3/Cr2O3 CERAMICS HVOF SPRAYED COATINGS FOR PROTECTION AGAINST SILT EROSION

Hydro turbines are one of the most vital and essential components for the production of hydroelectric power. Since the hydro turbine is always operating under the influence of water and the silt transported by the water from the hilly region, it poses a lot of threat and damage to the turbine blades working constantly under the action of silt laden water. Erosion wear is the most common type of damage, and drastically affects the life of turbine runners and blades. The introduction of thermal spray coatings, namely high-velocity oxy-fuel (HVOF) technique, has resulted in a major improvement in stainless steel erosion resistance. Ceramic coating powders primarily Al2O3, Cr2O3, and a composite mixture of composition 55% Cr2O3+45% Al2O3 were deposited on stainless steel substrates of grade 304. The thorough experiments utilizing silt slurry are conducted at different particle size of silt in the range 212–250, 150–212 and 53–106 μm. The silt concentration has been varied in the range 12–42% by weight, and the substrate was rotated at a rotational speed in the range 600–1500rev/min for the test time of 4h. SEM images were used to assess the surface morphology of the required testing samples. The erosion observance and the material removal mechanism were investigated and discussed on the basis of microstructure studies. Cr2O3 coating is found to be more resistant to erosion than other coatings under all test conditions.