Technological conditions of diffusive boride coating formation on silicon carbide and molybdenum disilicide

Abstract

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...