Enhancing high-temperature resistance of structural steels by forming nickel-based coatings via non-vacuum electron-beam cladding

Nickel-based coatings were fabricated on 0.4 wt.% C-Cr structural steel substrates via non-vacuum electron beam cladding (NVEB cladding), using Colmonoy-227F self-fluxing powder. This study presents results on the microstructure and properties of single-, double-, and triple-layer coatings. The optimal electron beam current for the formation of defect-free alloyed coatings is 23 mA. The thickness of single-, double- and triple-layer coatings is 2.7 mm, 3.4 mm and 4.4 mm, respectively. The coatings have a dendritic structure with crystals of the first and second order. Microstructural analysis revealed that single- and double-layer coatings consisted primarily of a γ-FeNi substitutional solid solution. The application of a third layer led to precipitation of Fe1.8Ni1.2P phosphide and FeSi2 silicide phases. A decrease in iron content within the coating with an increasing number of layers was observed, which correlated with improved resistance to high-temperature oxidation. The paper presents the results of a comparative study of high-temperature oxidation in an air atmosphere at 850°C for 100 hours of 0.4 wt.% C-Cr steel and single-layer, double-layer and triple-layer nickel-based coatings. It was found that the weight gain of 0.4 wt.% C-Cr steel was 60.81 mg / m2, while for the deposited coatings the values were significantly lower: 17.87 mg / m2 (single-layer), 11.22 mg / m2 (double-layer) and 7.01 mg / m2 (three-layer). X-ray diffraction (XRD) analysis revealed that the oxide films formed on the deposited coatings consisted of iron oxides (Fe3O4, Fe2O3) and spinel NiFe2O4. A factor that increases resistance to high-temperature oxidation is the formation of protective spinel, which prevents the diffusion of oxygen and metal. Consequently, the triple-layer coating exhibited an 8.7‑fold increase in resistance to high-temperature oxidation in air compared to the 0.4 wt.% C-Cr steel substrate alone.

1. Ministry of Education and Science of Russia - project FSUN-2023-0009