Novosibirsk State Technical University (NETI) together with the Institute of Nuclear Physics SB RAS named after G. I. Budker creates protective coatings using surfacing of metal-containing powder mixtures on steel products with a beam of relativistic electrons released into the air atmosphere. The work is carried out within the framework of a grant from the Russian Science Foundation and is aimed at the formation of "steel-coating" compositions, the surface layers of which provide high indicators of both wear resistance and corrosion resistance (heat resistance) of materials used in mechanical engineering for the manufacture of responsible products.
"The working conditions of modern equipment in most industries place increased demands on the materials used for its manufacture. During operation, some parts are simultaneously exposed to aggressive environments, such as acids, high temperatures, water vapor, and various types of abrasive particles. The combined effect of these negative factors causes intense destruction of the surface layers of materials, which eventually leads to premature equipment failure. One of the solutions to this problem is related to the formation of multifunctional coatings on the surface of the parts, the level of operational properties of which significantly exceeds the properties of the main material of the product. In this regard, the main objective of the project is to develop a cost—effective coating that provides a multiple increase in the life of trouble-free operation of products in the oil and gas and chemical industries," said Ekaterina Drobiaz, Associate Professor of the Department of Materials Science in Mechanical Engineering at NSTU-NETI, Candidate of Technical Sciences.
To form multifunctional coatings, a unique industrial electron accelerator ELV-6 was used which was developed at the Institute of Nuclear Physics SB RAS named after G. I. Budker. The high electron energy (up to 2.5 MeV) makes it possible for the electron beam generated by the accelerator to penetrate into the layer of deposited powder and simultaneously melt it. In addition, the energy reserve is sufficient to melt the thin surface layer of the base material of the product. Active mixing in the liquid state of the components of the surfacing mixture and the base material leads, upon subsequent cooling, to the formation of a coating up to 5 mm thick. The wide transition zone between the coating and the base material of the product ensures high adhesive properties of the steel-coating composition.
"The most important factors determining the performance properties of coatings are the composition of the materials applied to the surface of the workpieces and the structure that occurs at the stage of crystallization of the liquid bath. Our task as developers was to select the compositions of the deposited powder compositions, as well as to work out the modes of formation of high-quality multifunctional coatings. A high level of wear resistance is usually provided by high-strength dispersed ceramic particles. When developing surfacing compositions, the main choice fell on boron compounds. Borides are characterized by high hardness, strength and chemical resistance in aggressive environments. In addition, the surfacing mixtures include microadditives of corrosion-resistant and refractory components of tantalum and chromium. Their rapid ability to form a passivating film when exposed to acids leads to an increase in the corrosion resistance of the coatings being developed," said Evdokia Bushueva, Candidate of Technical Sciences, Associate Professor of the Department of Materials Science in Mechanical Engineering at NSTU-NETI.
During experimental studies, the wear resistance of materials under various abrasive conditions, corrosion resistance in nitric acid, and heat resistance of the developed materials were evaluated. The high hardness of borides, reaching 25 GPa, leads to a sixfold increase in the wear resistance of the developed coatings compared to stainless steels. Surfacing powder compositions make the greatest contribution to heat resistance. The maximum increase in relative heat resistance at a temperature of 850 ° C is observed in the deposited layers of the composition Ta-Nb-CrB — 6 times higher than the resistance of stainless steel. Some types of coatings have high heat resistance at a temperature of 950 °C.