METHOD OF OBTAINING CERAMIC MATRIX COATING ON STEEL, WORKING IN HIGH-TEMPERATURE AGGRESSIVE ENVIRONMENTS

摘要

FIELD: materials science.;SUBSTANCE: invention relates to materials science, including the creation of protective ceramic matrix coatings on a steel surface with high corrosion resistance in aggressive media at temperatures of contact interaction 400–600 °C due to changes in the composition and structure of their surface layers. Invention can also be used in chemical industry. Method consists in the fact that a powder of pure aluminum with a fraction of 20–60 microns is applied to a steel surface by supersonic cold gas-dynamic spraying. Air is used as the working gas. Composite powder consisting of 20 % corundum with a fraction of 50–60 microns and 80 % of aluminum powder with a fraction of 20–60 microns, reinforced with over 50 % nanoscale corundum particles with a fraction of up to 100 nm, is applied to the formed aluminum first layer by supersonic cold gas-dynamic spraying. Air is used as the working gas. When spraying, clusters of nanocorundum are formed, which fill the coating pores. Next, the resulting aluminum hardened second layer, having porosity of not more than 5 % by volume, is subjected to microarc oxidation in silicate-alkaline electrolyte of the following composition: sodium silicate – 9 g/l, potassium hydroxide – 2 g/l, the rest is water. Duration of microarc oxidation is 1–1.5 hours; an external ceramic oxide MAO layer is formed inside the hardened second aluminum layer with corundum nanoparticles with an open porosity of not more than 7 %. This method allows to reduce the number of operations during formation of ceramic matrix coating. Surface of the obtained ceramic matrix coating has microhardness of 15–20 GPa, the adhesion of the coating to the metal base is at least 50 MPa. In the interaction of the surface with an aggressive environment at temperatures of 400–600 °C an outer MAO layer and a hardened aluminum second layer with corundum nanoparticles provide protection for the ceramic matrix coating from destruction and create the necessary conditions for the formation of an Al-Fe intermetallic layer with porosity of no more than 2 % of the volume of the entire thickness of the first aluminum sublayer, due to the actively flowing diffusion at a “substrate-coating” boundary. At the same time, the coating adhesion to the steel deteriorates by no more than 5 %.;EFFECT: intermetallic first layer of Al-Fe protects the steel from interaction with aggressive media, in case of its partial penetration into the pores of wear-resistant external and second layers of the ceramic matrix coating.;5 cl, 2 ex