Sirak Y. The effect of copper and nickel on the formation of plasma electrolytic layers in the aluminum thermal spray coatings

The work is devoted to the study of the influence of alloying elements (of the copper or nickel) inside thermal spray coatings on the mechanism of the plasma-electrolytic oxidation and on the physical and mechanical characteristics of the PEO layers. It was first established that during the synthesis of aluminum thermal spray coatings alloyed by such metals, whose oxides are restored by an aluminum melt in the plasma channels, the metal oxide composite layers based on the corundum with the ductile metal inclusions (of the copper or nickel) are synthesized instead the simple oxide layers. Such composite layers have enhanced of the tribological characteristics and wear resistance at the cyclic and impact loading. The optimum content of the copper or nickel in the layer was 5...10 wt. %. Based on thermodynamic calculations and their experimental approbation, the models for the synthesis of copper- and nickel-containing oxide layers on the alloyed of thermal sprayed coatings during their plasma-electrolytic treatment (micro arc oxidation) in alkaline electrolytes have been developed. It was established the sequence of the reactions occurring in the plasma channels and the relationship between the energy of a single plasma discharge during the synthesis of the PEO layer and the size of the metallic inclusions in it. It was first revealed the selective mass transfer effect at the conditions of the boundary lubrication during frictional interaction of a friction pair - a PEO layer with the inclusion of dispersed copper inclusions (as a disk) - a cast iron (as a liner) - in an oil with addition of 1% aqueous glycerin solution (2.5% vol.). As a result of this effect the coefficient of friction and the amount of wear of a liner was reduced by an order of magnitude.