Experimental studies on fly-ash erosion behavior of Ni-Cr based nanostructured thermal spray coating in boiler tubes

Erosion study was performed on the uncoated and coated SA210Gr-C boiler tube substrates. This study was performed in a view to reducing the scaling on boiler water-wall and super-heater tubes. In the present work, the High Velocity Oxygen Fuel (HVOF) coating process was used to deposit nanostructured and conventional coatings on the boiler tube substrates. Fly-ash produced after the combustion of coal in an Indian thermal power station was used as erodent. The erosion loss of coated and uncoated substrates was recorded at a regular interval of 30 minutes. The study was conducted at 30 degrees, 60 degrees, and 90 degrees impingement angles and at two different operating temperatures (300 degrees C, 550 degrees C). Surface morphology of eroded samples was analyzed using macro and micro imaging techniques, and surface roughness was also recorded for the eroded samples. The phases present in the eroded substrates were indexed using the X-Ray diffraction (XRD) analysis. HRTEM images of nanostructured coated samples at 550 degrees C with varying impingement angles were analyzed. The result reveals that the nanostructure in the coating was retained even after high-temperature erosion test. Comparative study was made with nanostructured and conventional coatings against the uncoated materials.