OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 2 2023 Fig. 4. Microstructure of the 1st specimen after plasma-jet hard-facing: a, b, c – the upper part of coating; d – the lower part of the coating near the boundary with the base metal а b c d the microstructure is also represented by eutectic colonies of Fe2B and α-Fe, but the width of this layer has increased and is 200 µm. Figure 7 shows the microstructure of the hard-faced layer of the third specimen after plasma-jet hardfacing. It has a hypoeutectic structure consisting of boride eutectic and primary dendrites of a α-solid solution of boron in iron. According to the X-ray analysis data (figure 8), the main phases of the coating are Fe2B and α-Fe. The boron content in the hard-faced layer is 3.4 %. It can be seen that these microstructures are in a good agreement with these phase diagrams when considering binary phase diagrams of Fe–B [18]. It is known that alloys of iron with boron are of eutectic type, where the eutectic is formed by a solid solution of α-Fe and Fe2B. At a boron concentration of 3.83 wt.%, the alloy is 100 % eutectic. In the course of studying the microstructure of the hard-faced layer after plasma-jet hard-facing, the boron content was determined by the layer depth using the electron probe micro analyzer method. The results of determining the boron content by the depth of the hard-faced layer are shown in figure 9. It can
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