Abstract
Thermal spray conditions have important effects on the formation mechanism of a coating lamination. When thermal spray distance or power is changed, there is an increasing chance of defect being generated during coating formation. Thermal spray distance was chosen from each of 80, 100, 150 and 200 mm. The cavitation erosion strength of the sprayed coatings under the above conditions was examined. The evaluation of cavitation erosion of Al2O3 coatings was investigated by magnetostrictive cavitation test at a frequency of 20 kHz and at a horn amplitude of 50 μm. Cavitation erosion at the thermal spraying distance case of 200 mm was five times greater than that at the distance of 80 mm. The results of X-ray diffraction showed that α-Al2O3 tended to disappear when thermal spraying distance was the longest case of 200 mm. This is attributed to the temperature decrease of particles. The following factors are considered as the reason of the above phenomena. When the distance between the substrate and spraying nozzle is long, the flight time of particles becomes longer. During that time, the heat capacity of particle decreases, which in turn reduces the expansion rate and cohesion strength.
Gas hole was made to be an origin, and it seemed to propagate the fracture damage for defects, voids or cracks, etc.
