PROPERTIES OF NI-P-W COATINGS AND TECHNOLOGICAL FEATURES OF THEIR ELECTRODEPOSITION

A study of the electrodeposition of Ni-P-W coatings from pyrophosphate and citrate electrolytes was conducted. It was shown that for active inclusion of tungsten in the coating, it is advisable to use a citrate electrolyte with a temperature of 70 °C, which allows obtaining coatings containing 11.5% P and 5% W without microcracks. Heat treatment of the coating of this chemical composition at 350 °C leads to an increase in microhardness to a value of 10.1 GPa, which corresponds to hard chromium plating. In this case, a nanocrystalline structure is formed, consisting of the Ni3P and Ni5P2 phases, and a nickel-based solid solution. Due to the mutual diffusion of the base metal and the coating during annealing, the adhesion of the coating increases on both carbon and stainless steels. Exposure of steel samples with a Ni-P-W coating to 3.5% NaCl showed that the coating has high corrosion resistance. In general, the level of properties of the
Ni-P-W coating corresponds to hard galvanic chromium, but does not have microcracks.