RESEARCH OF PLASMA COMPOSITE COATINGS FROM OXIDE AND NICKEL BASE ALLOY
Keywords:
plasma jet, coatings, shielding elements, ratio of powder use, plasma flows, cubic modification, zirconium dioxideAbstract
The results of a study of the influence of plasma jet parameters and the fractional composition of the initial powder on the characteristics of two-layer composite coatings based on nickel-chrome and zirconium dioxide on elements of protective screens are presented. Optimization was carried out based on obtaining the maximum powder utilization rate. A comparative analysis of the dependence of the powder utilization coefficient of viscous metal layers of nickel-chromium and nickel-aluminum on the spraying distance shows that with a similar nature of the curves of the presented dependences in absolute value, the values of the powder utilization coefficient are greater under optimal conditions for nickel-chromium powder. This can be explained by the high plasticity of the latter and, accordingly, less rebound of particles colliding with the substrate. The results of studies of the microstructure of cross sections of the formed coatings, carried out using scanning electron microscopy, are presented. The microstructures of the cross sections of the ZrO2 coating and the Ni–Cr intermediate layer are considered. From the presented data it is clear that in the initial state the coating is characterized by porosity, with the average pore size being several micrometers and in some areas reaching 20 microns. The microstructure of the Ni–Cr layer is characterized by lower porosity. The effect of compression plasma flows on the sprayed coating leads to the formation of a remelted oxide layer 12–15 µm thick, promotes smoothing of the surface topography and the formation of cracks on the surface, propagating mainly into the depth of the coating. Treatment of oxide coatings with compression plasma also leads to a decrease in their porosity.
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