CAVITATION-EROSION WEAR RESISTANCE OF COMPOSITE ELECTROLYTIC COATINGS IN NEUTRAL MEDIUM.

The technology of forming wear-resistant composite electrolytic coatings on the nickel base is given in the paper. The CEC contained the filler of powders of silicon carbide of various factions: nanopowders of up to 50 nm, 5 (M5) μm, 20/28 μm, 40/50 μm and amorphous boron with the size of particles of about 1 μm to form solid solutions during further heat treatment. Accordingly, the following designations are accepted in the paper: Ni-SiC_nano; Ni-SiC₅; Ni-SiC₂₈; Ni-SiC₅₀. The setting to form the CEC was built which allows adjusting the resistance of the near-electrode layer of electrolyte, which in turn, allows forming the CEC in a wide range of technological parameters of electrolysis both on horizontal and vertical cathodes (Patent of Ukraine №55154 from 10.12.2010.). The study of cavitation-erosion wear resistance in hard water and in 3 % solution of NaCl showed that the CEC formed can be divided into 2 groups: group I - CEC of the composition Ni-SiC_nano and Ni-SiC₅ and group II - CEC of Ni-SiC₂₈, Ni -SiC₅₀. Thus, the CEC of Ni-SiC_nano and Ni-SiC₅ (group I) are the most effective to enhance cavitation-erosion wear resistance of parts which are operated in sodium chloride solutions, particularly in sea water (3 % solution of NaCl). Thermal annealing at 400 oC for 1-2 hours increases the cavitation wear resistance of the CEP Ni-SiC_nano by 20 % in hard water and 30 % in NaCl solution due to the increase of micro-hardness, leveling of internal tension of coating and increase of corrosion resistance by reducing the electrochemical heterogeneity. Vacuum annealing of the CEC with particles of silicon carbide and boron at 1080-1090 oC allows to obtain dense and smooth coatings, the cavitation wear resistance of which increases on average more than 2 times as a result of formation of a solid frame from eutectic Ni-Ni₃B and borides Ni₃B. [ABSTRACT FROM AUTHOR]