OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 4 2022 a b c Fig. 4. Distribution of elements in the metal-oxide layer (3 in Fig. 2): a – image in secondary-electron mode; b – in the characteristic X-ray radiation of iron; c – in the characteristic X-ray radiation of oxygen The inner layer (1 in Fig. 2) has a complex phase composition. Areas formed from molten undeformed and plastically deformed particles of the initial powder, as well as from deformed particles that have not had time to melt, are clearly distinguishable in its structure (Table 3). The particles of the first kind have managed to solidify before impact on the substrate; therefore, it has a practically initial round shape and a pronounced dendritic structure (1 in Fig. 5). The second-type particles have solidified directly on the substrate under deformation, and it has a polygonal structure without dendrites (3 in Fig. 5). The third grain type in the coatings studied (2 in Fig. 5) is represented by unmolten initial powder particles heated and deformed during collision with the substrate surface. The phase X-ray diffraction analysis has shown that the matrix in the coatings is constituted by solid solutions, namely, chromium ferrite for the coating of composition 1 (Fig. 6а) and ferrite + austenite for the coating of composition 2 (Fig. 6b). Fine carbides, silicides, and borides are the strengthening phases (Fig. 6). The second layer consists of the same phases as the first one, but with a higher content of ferrite formed during Fe powder spraying. In these ferrite grains there are no strengthening phases; therefore, it plays a role of dampers relaxing the arising thermal stresses. This layer provides smooth variation of the properties from layer to layer in the coatings. In this case, the porosity of the second layer is a positive factor since, during operation, under conditions of friction forces, the outer oxide layer penetrates into the pores of the Ta b l e 3 The chemical composition of the grains of the high-temperature coating marked in Figs. 5, at.% Coating of composition 1 (Fig. 5, a) Grain No. B C Si V Cr Mn Fe 1 13.5 2.0 4.5 1.1 4.5 2.6 71.7 2 9.9 0.9 3.1 1.4 6.5 3.5 74.3 3 14.9 1.3 7.4 0.8 14.2 1.5 59.7 Coating of composition 2 (Fig. 5, b) Grain No. B C Si V Mn Fe Ni 1 13.5 2.2 3.6 0.3 3.6 69.1 7.5 2 6.8 1.3 4.5 0.3 4.1 75.2 7.5 3 7.3 0.6 5.2 0.3 3.3 75.6 7.6
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