OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 1 2025 From Table 2 and the graphs (Figs. 4, 5, 6), it is evident that the hardness at the surface increases significantly and gradually decreases to 2,500 MPa as the distance from the surface increases. The decrease continues until it reaches the value characteristic of the initial state, before implantation. Thus, the maximum value of surface microhardness is observed in the samples after implantation by nitrogen ions at a dose of 5×1017 ions/cm2. This, consequently, is the most optimal dose of ion implantation for cast iron samples (type CI20), which is shown under the given conditions of research. The increase in microhardness at the surface layer is related to the formation of a large number of specific radiation defects in the near-surface layer (such as, for example, Frenkel pairs) and the formed phases, in this case nitrides, which are known to have a high hardness (microhardness) value. Analyzing the obtained data on the hardness of the surface layer of the samples and the data obtained from the microstructural analysis results (obtained at different radiation powers), it can be seen that the thickness of the implanted nitrogen layer in our grey cast iron samples directly depends on the implantation dose. The higher the radiation dose, the wider the layer. However, the dependence is not linear. Apparently, with an increase in the implantation dose, the layer thickness may reach saturation, when all available interstitial sites in the crystal lattice of iron are filled with nitrogen atoms. For example, the increase in hardness for the implanted layer at a dose of 1×1017 ion/cm2 starts from approximately 75 µm from the surface; for 2×1017 ion/cm2 it starts from approximately 90 µm from the surface and for 5×1017 ion/cm2 it starts from approximately 90–100 µm from the surface. A similar pattern is observed for the hardness of the layer closest to the surface. Increasing the radiation power from 1017 ions/cm2 to 2×1017 ions/cm2 resulted in an increase in its hardness by approximately 2,000 MPa. Further increase of radiation power from 2×1017 ion/cm2 to 5×1017 ion/cm2 resulted in an increase in hardness of this layer by 3,500 MPa. X-ray Diffraction Analysis Results X-ray analysis was conducted to determine the phase composition and study the fine structure (average dislocation density and the size of mosaic blocks). This analysis demonstrated that during ion implantation of nitrogen into grey cast iron new phases are formed. The nitrogen ions, penetrating into the material, enter into chemical reactions with iron (Fe) atoms, which constitute the cast iron matrix. As a result of these interactions, iron nitrides are formed. Among it, the Fe3N phase, iron (III) nitride, predominates. In addition, iron (II) nitride, Fe2N, is present in smaller quantities. The formation of these nitrides is a consequence of the ion implantation process and has a significant impact on the properties of the surface layer of cast iron, Fig. 6. Change in microhardness of cast iron implanted with nitrogen ions at a dose of 5×1017 ion/cm2
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