SEREDA B. & PALEHOVA I
Study of the formation of multicomponent titanium coatings on steels under non-stationary temperature conditios.
The studies were carried out under the conditions of chemical- thermal surface treatment method.
In order to improve the reliability of equipment, reduce the cost of its maintenance, increase the service life, titanium-based coatings are widely used. Since in difficult operating conditions one-component titanium coatings are not able to provide the necessary working properties of products, it is advisable to saturate the metal surface with several elements. Joint saturation of Ti, Al and Si steels allows not only to increase the hardness of the surface layer, heat resistance and corrosion resistance of products, but also to increase the thickness of applied coatings and accelerate the process of their formation. Surface hardening of products from structural and alloyed steels is widely used methods of chemical-thermal surface treatment (HTO). HTO technology is a fairly effective method of surface hardening aimed at obtaining continuous, non-porous and resistant protective layers in aggressive media, which have good adhesion to the substrate. However, this method of processing is characterized by a considerable duration of technological processes (10-15 hours), resource and energy consumption. The aim of the work was the development of powdered SHS- mixtures for the deposition of multicomponent coatings on the basis of titanium in the regime of thermal autoignition, the study of the physicochemical processes of coating formation, the determination of the optimum technological parameters of the SHS process in complex saturation, the study of their influence on the kinetics of layer growth and their evaluation quality. The choice of the optimum mixture composition for conducting SHS- processes in the conditions of thermal autoignition was carried out based on the results of studies of the thermal picture of the SHS- process and the physical and mechanical properties of the protective coatings.The efficiency of processing is determined by the time parameters of the processing process and the thermophysical characteristics of the charge.It has been experimentally established that with an increase in the processing temperature and an increase in the duration of isothermal aging, the thickness of the diffusion layer increases.Coatings obtained in SHS processes consist of the film of the deposited product and a wide gradient diffusion zone, which is why they have improved characteristics in comparison with diffusion analogs, and are also characterized by high adhesive strength. When diffusion of noncarbide-forming elements in γ-iron after reaching the solubility limit, γ → α-transformation occurs. In α-iron, the solubility of carbon is negligible, so it is pushed back into the substrate with the formation of a zone with a high content of carbon under the coating. With increasing content of aluminum and silicon in the charge, the thickness of the coating increases, however, to achieve high concentrations of all saturating elements in the coating, the content of Si and Al in the charge is recommended to be limited to 10% by weight. The density, porosity and roughness of the coatings depend on the Si content of the mixture, with an Si content of ~ 10% by weight. pores have a predominantly rounded closed form. With an increase in the concentration of silicon in the charge, the roughness of the coatings increases, the height of microroughness reaches 15- 20 micronsWhen studying the protective layers on the PMT-3 device it was established that the microhardness of the α-solid solution is 350-200 HV, the microhardness of the complex silicide on the surface of the steels is 1100-1000 HV. Conducted tests of SHS coatings for corrosion resistance showed an increase in this index by 1.5-1.8 times compared with the diffusion analogue.