Analysis of surface finish influence on erosive wear resistance of Fe-Cr-B-Mn coatings in boiler tubes exposed to fly ash
摘要
The protection of boiler tubes against erosion caused by fly ash is essential for maintaining boiler efficiency. This study proposes a metallic coating based on Fe–Cr-B-Mn, applied using the electric arc thermal spray technique, as an alternative for protecting the most impacted areas of boiler tubes from ash erosion. The impact of different surface finishes, obtained through grinding, on the erosive wear resistance of the coating was analyzed. The electric arc thermal spray was performed manually at an angle between the gun and the plate of 90 degrees, in atmospheric air. The coating’s surface roughness (Ra) was measured with a rugosimeter, in 2 preferential directions, and was found to have values between 11 and 17 μm. Grinding was chosen as the machining process due to its efficiency in finishing thermally sprayed surfaces. Three conditions were analyzed: as-coated (Ra = 13.08 µm), the intermediate surface finish (Ra = 2.495 µm), and the surface fine finish (Ra = 0.486 µm). Samples in all conditions were submitted to erosion tests according to ASTM G76, using alumina blasting. The surface was examined by scanning electron microscopy (SEM). The morphology of machining scars demonstrated a brittle failure mode of material removal during grinding. Additionally, the cross-section was investigated using optical microscopy. Abrasive wear tests presented average erosion rates of 3.038 × 10−5 g/s, 2.23574 × 10−5 g/s, 2.77325 × 10−5 g/s for fine, intermediate, and as-coated finishes, respectively. The results guided the optimized selection of materials and processes to protect boiler tubes from fly ash impact.