Мardarevych R.S., Vуnar V.A., SlepkoR.T., Vasyliv Kh.B. Effect of thermal treatment on the tribocorrosion resistance of nickel-based galvanic coatings.
Keywords:
nickel-based galvanic coatings, heat treatment, tribocorrosion, hydrogen, friction coefficientAbstract
The tribocorrosion behavior of nickel-based galvanic coatings before and after thermal treatment has been investigated. The influence of hydrogenating on the tribotechnical characteristics of the coatings in a 0.5 M aqueous solution of sulfate acid has been studied.
Galvanic nickel coating of 50 ... 60 μm thickness was applied to samples in sulfate chloride electrolyte. Composite electrochemical nickel-boron coating (CPE) of a similar thickness was applied from a suspension of amorphous boron in a sulfate chloride electrolyte of nickel. The developed chemical composition of the bath, the parameters of electrolysis and the hydrodynamic modes of mixing the suspension provide electrodeposition of a high-quality composite nickel-boron layer with a homogeneous distribution of boron particles and their content in the nickel-matrix of 4.8 ... 5.3 mass%. Nickel-phosphorous coating was applied by the method of chemical precipitation from acidic electrolyte. Thickness of coating was 25 ... 28 mm and phosphorus content was 11 ... 12.5 mass%. Thermal treatment of samples with coatings was carried out by annealing in a vacuum furnace at 450°C for 1 hour. Samples from Ni-B CPE were additionally annealed at 900°C for 1 h.
Tribocorrosion studies of plates 50×40×5 mm with coatings were carried out according to the scheme of friction "plane-sphere" with the reciprocating displacement of contacting surfaces. The load on the indenter (Al2O3 ball, Ø9 mm) was 2 N. Material losses were determined by the width of the friction track.
It is established, that cathodic polarization reduces wear-resistance of coatings in 1,2 ... 2,3 times. An electrochemical composite Ni-B coating after annealing at 900°C forms a new heterogeneous structure. It consists of a solid nickel solution and Ni3B boride grains inclusions. High hardness and sufficient resistance to hydrogen determine the increased wear resistance of this composition compared with others. Hydrogenating of the Ni-P coating at the friction reduces wear by 2.1 times.
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