The recommended ways of improving the technological and physico-mechanical properties of refractory metals (molybdenum and tungsten) after diffusion saturation with the elements of the same name are described. In order to increase significantly the performance characteristics and transition to stricter operating conditions for products made of refractory metals, it is necessary to improve the existing methods of processing metals and make significant changes in the development of new ones. Different directions of refractory metals processing, which involve diffusion saturation with elements of the same name, introduction of activating additives into the composition of the diffusion mixture, use of isothermal conditions during chemical-thermal treatment, and application of protective coating to improve technological and physical-mechanical properties, have been studied and analyzed. To evaluate changes in the mechanical properties of molybdenum and tungsten after diffusion saturation with the elements of the same name, appropriate tests were conducted. To study the changes in the technological and physical and mechanical properties of refractory metals after the process of diffusion saturation in active-aggressive environment, tests on static rupture and stretching, bending, impact bending and buckling were carried out. It has been established that it is possible to increase the technological characteristics and ensure the use of refractory metals in harsher operating conditions by introducing molybdenum and tungsten powders of the same name and activating additive (sodium fluoride) into the charge to obtain protective coating. Comparison of the magnitude of the temporary resistances values for of untreated samples breaks of refractory metals and samples that have undergone the appropriate heat treatment showed significant decrease in these indicators after diffusion saturation with the same elements (molybdenation and tungstenization). Based on the analysis of literature data and conducted research, a set of measures aimed at the improvement of technological and physico-mechanical properties of refractory metals (molybdenum and tungsten) after diffusion saturation with the same elements in powder medium is proposed.

Basic directions of the diffusive boride coating formation on reaction-sintered silicon carbide and molybdenum disilicide are described. Technological conditions of non-metal ceramic materials boriding depending on the consideration of the amorphous boron concentration in the powder mixture are investigated and analyzed. It is determined that it is possible to speed up the rate of saturation process of the silicon carbide and molybdenum disilicide with boron by introducing sodium and aluminum fluorides as activating agents. Based on the carried out researches, optimal conditions for choosing the concentration of activating agents providing high saturation speed and improve operational parameters of the products are offered. It is also defined that to stimulate the process of boriding reaction-sintered ceramic materials, titanium hydride should be introduced into the saturated environment as the activating agent. Diffusion saturation of metals and alloys in hydrogen environment provides high saturation rate and good quality of the treated surface. The results of the carried out investigations prove that the saturation ability of the boride mixture increases significantly by introducing sodium fluoride and titanium hydride into it.Statement of the problem. The technological process of diffusion siliconazing of reaction-sintered silicon carbide and molybdenum disilicide does not provide complete binding of the harmful impurities formed in the material while producing the products [1,2]. The availability of harmful impurities, particularly, silicon dioxide, results in significant degradation of technological and operational parameters of SiC and MoSi2.Analysis of the available investigations and publications. One of the promising trends for improving the physical-chemical properties of reaction-sintered ceramic materials is diffusion saturation with boron resulting in the formation of silicon borides and other impurities. It is known that borides possess high oxidation resistance, which combines with the large thermal-shock resistance. They are chemically passive and have good radiating power and good thermoelectric parameters [3,4]. Relatively, the physical-chemical properties of reactionsintered ceramic materials should be improved. In our opinion, the technology of powder boriding method of silicon carbide and molybdenum disilicide for binding silicon and other harmful impurities is advanced. Hence, the process of diffusion saturation of SiC and MoSi2 with boron is investigated.The objective of the paper is to investigate the technological conditions for the formation of the diffusion boride coating on silicon carbide and molybdenum disilicide.Results of the investigation. The technological process of silicon carbide and molybdenum disilicide boriding was carried out in containers with fuse gate in the powder mixture containing amorphous boron, fluoride agent and aluminium oxide. The concentration of amorphous boron was changed from 5 to 40 %, and the saturation process was carried out at temperature of 1000 -1200...

The main methods for processing ceramic materials based on reaction-sintered silicon carbide and molybdenum disilicide are described. The technological conditions of nonmetallic ceramic materials processing depending on the oxide silicide composition in the powder mixture are studied and analyzed. It is determined that the increase in the lifetime of ceramic materials based on silicon carbide and molybdenum disilicide can be achieved by introduction of zirconium oxide, yttrium oxide and hafnium oxide. Based on the carried out investigations, optimal conditions for selecting the concentration of these additives, which ensure high saturation speed and improve the operational parameters of the products are proposed. It is also determined that in order to intensify the processing of ceramic materials based on reaction-sintered ceramic materials, various compositions of the silicide oxide composition can be introduced into the saturation medium. Diffusion saturation of ceramic materials with titanium hydride provides high saturation speed and good quality of the surface to be treated. The study of the kinetics of the interaction of silicoboride phase with the carborundum and disilicide with molybdenum base showed that, with increasing heating duration, the thickness of the diffusion coating decreases. The final operation of the process for processing reaction-sintered ceramic materials is to apply silicon-based surface of carbide-silicate and disilicide molybdenum samples of the suspension layer of silicide oxide composition containing molybdenum disilicide, zirconium-yttrium ceramics, and sodium aluminate. The proposed method of processing reaction-sintered ceramic materials increases in 2 and 1.5 times the lifetime of samples based on silicon carbide and molybdenum disilicide. The results of the carried out research show that the proposed method can be recommended for the processing of products based on reactionsintered carbide silicic acid and disilicide molybdenum materials used for the manufacturing the electric heaters and various types of structural elements of high-temperature equipment.

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Recommended ways to improve the chemical and physico-mechanical properties of reaction-sintered ceramic materials based on molybdenum disilicide have been described. In order to significantly increase the operating temperatures and change to more stringent operating conditions for ceramic products, it is necessary to improve existing methods of processing ceramics and significantly change the development of new ones. Various means for processing of ceramic materials have been studied and analyzed, which include the introduction of activating additives, hardening with dispersed particles, filamentary crystals and fibers and application of a protective coating to prevent rapid oxidation at surface layers. Carrying out partial purification of the initial starting components from various impurities can significantly increase some characteristics of the disilicide of molybdenum ceramics. Disilicide of molybdenum ceramics has been researched to have significant influence on the physical and mechanical properties (thermal conductivity, electrical resistance, coefficient of thermal expansion and strength) of molybdenum ceramics disilicides, which are introduced into the base material both with the initial components and in the process of its technological production. It has been established that it is possible to increase operating temperatures and ensure the use of molybdenum disilicide-based ceramic materials in harsher working conditions can be achieved by introducing of aluminum, boron, beryllium, iron, yttrium, nickel and cobalt powders into the charge, strengthening titanium coating, which includes silicification and titanium technology. It has been researched that at high temperatures and in the presence of molten silicon the synthesis and crystallization of molybdenum dicilicide occur on the grains in the surface layers, as well as dissolution and recrystallization of submicron particles of molybdenum dicilicide take place at certain depth. Based on the published data analysis and conducted research, the complex of measures for improving the chemical and physico-mechanical properties of reaction-sintered ceramic materials based on molybdenum disilicide has been proposed.