Structural features and tribological properties of multilayer high-temperature plasma coatings

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 To measure the roughness parameters and obtain 3-D profilometry of the surfaces of the coated specimens in the initial state and after testing, a non-contact profilometer-profilograph Optical profiling system Veeco WYKO NT 1100 was used. Results and discussion Determination of the structure and phase composition of coatings The results of metallographic studies showed that the formed multilayer coatings consist of sequentially applied layers with the total thickness of the entire coating up to 800–850 μm. Figure 3 shows the microstructure and distribution of elements in the obtained coatings. Previously performed phase X-ray diffraction analysis [17] showed that the first (metal) layer of coating A of composition 1 (denoted by number 1 in Fig. 3 a) consists of a solid solution of Cr, Si and Mn in α-Fe with strengthening phases in the form of carbides and silicides of chromium and manganese (Cr23C6, Cr5Si3, CrSi, Cr3Si and Mn5Si3) and iron borides FeB (Fe2B). The metal layer of coating B of composition 2 (denoted by number 1 in Fig. 3 b) consists of two solid solutions of ferrite (α-Fe) and austenite (γ-Fe). The strengthening phases are dispersion carbides, silicides and borides (NiSi2, Ni3Si2, Mn5Si3, Fe5Si3, Fe2B). The second (transition) layer and the outer (oxide) layer (denoted by numbers 2 and 3 in Fig. 3 a and b) on both coatings consist of an α-solid solution based on Fe and oxides FeO, Fe2O3 and Fe3O4. Determination of micromechanical properties of sprayed coatings Based on the results of instrumental microindentation, it was found that the highest level of microhardness was possessed by the first metal layer (1) for coating A the microhardness was 1,030 HV 0.1. The first (metal) layer (1) in coating B was characterized by a microhardness of 745 HV 0.1. The increased hardness of the metal layer of coating A is associated with a high content of strengthening phases in it. The microhardness of the transition layer (2) is 650 HV 0.1 for coating A and 580 HV 0.1 for coating B. The microhardness of the outer oxide layer (3) for both coatings is 290 HV 0.1. The variation of microhardness in related areas reaches ~ 350–380 HV 0.1 for coating A and ~ 150–300 HV 0.1 for coating B, which is explained by a decrease in the volume fraction of the strengthening phase (Tables 2 and 4). The strengthening phases in the coatings reduce the values of maximum and residual indentation depths hmax and hp, which leads to an increase in the values of indentation hardness at maximum load HIT (meaning an increase in resistance to permanent deformation) and Martens hardness HM, which takes into account both plastic and elastic deformation, the indentation elastic modulus E* of both coatings changes insignificantly (Fig. 4 a and 5 a in Tables 2 and 4). In earlier studies [18, 19] it was shown that such parameters as elastic recovery Re, (characterizes the share of elastic deformation in the total deformation during indentation), and indices of the plastic component of work φ and creep CIT are used to assess the resistance of surface layers to mechanical action. Specimen Fig. 2. Tribological loading scheme “pin-on-disc”

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