OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 1 2023 The saturating mixture included powders of boron carbide, aluminum and copper oxide. Sodium fluoride acted as an activator of the saturation process. The composition of the saturating mixture had the following percentage of components: 47 % B4C + + 28 % CuO + 23% Al + 2 % NaF. The optimal amount of copper oxide was chosen based on the works [21–23], where diffusion layers with maximum thickness were obtained. The prepared specimens were placed in a container, filled with a saturating mixture (Fig. 1, a) and placed in a muffle furnace (Fig. 1, b). To prevent oxidative processes, the lid of the container was sealed with fusible glass. Diffusion saturation was carried out at a temperature of 950 °C, for 3, 4 and 5 hours. Further, the container was cooled in air; specimens were extracted, cleaned out of the remnants of the saturating mixture. This was followed by the preparation of specimens for metallographic studies. a b Fig. 1. Packed containers (a), muffle furnace EKPS-50 (b) The specimens were fixed in clamps, then grinding and polishing were carried out. To identify the microstructure of the studied specimens, a chemically active solution consisting of nitric acid (4 %) and alcohol (the rest) was used. Metallographic studies were carried out on an optical microscope Altami MET 2C. Microhardness measurements were carried out on a PMT-3M microhardness meter, the load on the diamond pyramid was 50 g. Elemental analysis was conducted on a JEOL JCM-6000 scanning electron microscope (SEM) with an elemental dispersion analyzer. To study the structure, the etched surface of the specimens was studied in the mode of secondary electrons. X-ray phase analysis was performed on a D2 PHASER diffractometer with a LYNXEYE linear detector. The measurement step was 0.02°, the processing time of one step was 1.2 s. The study of the topography with the determination of the surface roughness parameters of the obtained specimens was carried out on an optical profilometer Bruker Contour GT-K1 with Vision64 software [24, 25]. Results and discussion As a result of diffusion surface saturation of specimens with boron and copper for 3 hours, diffusion layers with a thickness of 110–130 µm were obtained (Fig. 2). After diffusion borocoppering for 4 hours, diffusion layers with a thickness of 140–220 µm were obtained on the surface of the specimens (Fig. 3). Fig. 2, a shows a 120 µm thick diffusion layer of Steel 45 (0.45% C) with a hardness of 1,800–1,600 HV. The diffusion layer has a needle-like structure typical of the boride layer. A characteristic feature is the deep insertion of needles into the steel base, which many authors point out as the reason for the strong adhesion of the diffusion layer to the metal base [26–29]. In this case, the needles at the ends have rounding. The carboboride phase is isolated directly from boride needles, the hardness of which was 1,200–1,750 HV. The transition zone between the layer and the steel base does not differ from the ferrite-pearlite structure of the base.
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