Cavitation Resistance of Thermal Spray Coatings

Cavitation and erosion damage to hydroelectric turbines and pumps can be a major problem. The effectiveness of thermal sprayed cavitation-erosion resistant coatings for hydroelectric turbine and pumps was evaluated. The coatings evaluated were applied using High Velocity Oxyfuel (HVOF) and Plasma Spray systems. Hard facing cobalt based alloys were evaluated on coupons in the laboratory. Testing was performed using a cavitating jet erosion apparatus utilizing an operating pressure of 27.6 MPa. The results were compared to welded 308 stainless steel. Cavitation resistant austenitic stainless steel weld alloys were also evaluated. The results showed that the cavitation rate of the austenitic stainless steel weld alloys were as low as one third of the rate of the 308 stainless steel. The cavitation rate of the thermally sprayed hard facing coatings were more than three times higher than the rate of the 308 stainless steel. CERHAB glass enamel coatings containing 7 wt % wollastonite fibers were successful applied by using two combustion spray processes. The applied CERHAB coatings were successfully annealed using field portable heaters and may have application as a seal coat for thermal spray coatings applied in the field.