Abstract: In order to enhance the wear resistance and explosion-proof performance of the water-cooled walls in circulating fluidized bed boilers, Cr₃C₂-NiCr coatings were fabricated on 20G steel through high velocity oxygen fuel spraying technology. The impact of spraying distance (140, 200, 260 and 320 mm) on the particle binding state and erosion resistance of the Cr₃C₂-NiCr coatings was systematically investigated by means of scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), microhardness tester, and erosion wear tester. The results indicate that when the spraying distance ranges from 200 mm to 260 mm, the adhesion between NiCr and Cr₃C₂ particles is more optimal, and the anti-peeling capacity of Cr₃C₂ particles is significantly stronger. Compared with the powder, the phase composition of the coating prepared by high velocity oxygen fuel spraying does not exhibit substantial changes. The coating mainly consists of Cr₃C₂ as the dominant phase and NiCr as the adhesive phase. As the spraying distance increases from 140 mm to 320 mm, the porosity of the coating initially decreases and then increases, while the hardness of the coating shows an opposite trend. Specifically, when the spraying distance is 260 mm, the porosity reaches the lowest value of 3.61%. Under the synergistic influence of the adhesion strength of Cr₃C₂ hard particles, the porosity, and the uniformity of the NiCr phase distribution, the coating sprayed at a distance of 260 mm achieves the highest hardness, which is approximately 840 HV0.3. When subjected to the impact of high-speed particles at an angle of 90°, the coating with a spraying distance of 260 mm demonstrates the least erosion wear loss, with a value of only 3.7 mg. This value is 62.24% lower than that of the substrate. After the erosion test, a large number of "lip-like" morphologies are observed on the surface of the substrate due to the vertical force. In contrast, the "lip-like" morphologies formed on the coating surface are relatively shallow and sparse. In conclusion, the coating with a spraying distance of 260 mm exhibits the most excellent comprehensive properties.

Key words: high velocity oxygen fuel spraying, spraying distance, Cr₃C₂-NiCr coating, erosion resistance