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

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 а b c Fig. 1. Morphology of powder particles for obtaining a multilayer coating: а – powder of composition 1; b – powder of composition 2; c – Fe powder the inner layer. In order to create a surface scale layer, and to equalize the chemical composition of all layers and increase its adhesion, the coated specimens were subjected to high-temperature annealing at 1,000 ℃. The coating containing the first layer with chromium (composition 1 in Table 1) will be conventionally designated as coating A, and the coating with nickel-containing inner layer (composition 2 in Table 1) will be conventionally designated as coating B. Microstructure, chemical composition, structure features and thickness of the obtained coatings were studied on cross cuts by means of a TESCAN VEGAII XMU scanning electron microscope with an energy dispersive attachment of OXFORD HKLNordlysF+ at 100 to 800-fold magnification. By the microindentation method, using a Fischerscope HM2000 XYm measuring system with a Vickers indenter and WIN-HCU software at a maximum load of 0.980 N, the characteristics that reflect the features of the mechanical behavior of the studied coatings under elastic-plastic deformation were determined [16]. Strength indices (microhardness HV, HIT, HM and contact modulus of elasticity (E*)) and plasticity indices (elastic recovery (Re), work of plastic deformation (φ) and creep (CIT) during indentation) were determined. The values of Re, φ and CIT were calculated according to the formulas: max max 100% p h h h − = ⋅ Re ; (1) 1 100 % We Wt   ϕ = − ⋅     ; (2) max 1 1 100% h h CIT h − = ⋅ . (3) where We is a work of elastic deformation during indentation, released at removal of the applied load; Wt is a total mechanical work during indentation; h1 is a depth of indenter insertion; hmax is a maximum depth of indenter insertion. Investigation of tribological properties was carried out on a laboratory setup using the “pin-on-disc” scheme according to Fig. 2. The friction speed was 5 m/s at loads of 30, 75, 100 and 130 N. In each test, the sliding distance was 5,000 m. The “pin” specimens were made of A-coated and B-coated steel. The “disc” specimen was a disc made of 12 Cr-Mo steel. The tests measured the friction force using a leaf spring with resistance strain gauges glued on it. The heating of the friction surfaces occurred due to the friction itself; external heating sources were not used. The heating temperature of the friction surface was measured using a thermocouple mounted on a “pin” specimen near the friction surface.

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