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The kinetics of phase redistribution in the (Mo, W)Si2 Nb system at 1500-1800°C was investigated. The kinetic parameters for growth of the lower silicides (Mo, W, Nb) 5Si3 + Nb5Si3 and decrease in the layer thickness of the higher silicide (Mo, W)Si2 as function of the oxidation temperature were determined. It was established that the stability of the multiphase and multicomponent system was more than twice that of the system MoSi2 Nb, and 15-18 times that of MoSi2 Mo.  相似文献   
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This paper reports on the results of investigations of the development of high-temperature protective coatings on carbon-carbon materials, which are formed through vacuum activated diffusion saturation under conditions of liquid media and self-propagating high-temperature synthesis. The results of testing of the protective coatings in air at temperatures in the range 1600–1950°C are presented.  相似文献   
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The formation of high-temperature oxidation-resistant coatings on niobium by multicomponent activated diffusion saturation in vacuum is investigated. Thermodynamic calculations of potential chemical reactions that result in anticorrosive protective coatings are performed. Comparative tests of high-temperature oxidation resistance of niobium with protective coatings are conducted at 1700°C in open air.  相似文献   
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The effect of a subsurface layer of metal silicide on the phase composition stability of high-temperature MeSi2-type coatings on refractory metals was investigated. Using the system WSi2 W as a prototype it was experimentally determined that a subsurface layer of the tungsten disilicide, and the distribution profile of silicon in the diffusion zone upon high-temperature heating have a substantial effect on the formation of a barrier layer of lower silicide which determines the stability of the system as a whole. It is proposed that the search for more stable silicide coatings on refractory metals should be directed toward the creation of diffusion barriers on not only the inner interface MeSi2 Me, but also the external surface of the coating. The process of coating formation must be accompanied by the formation of a metal silicide on the external surface with the highest possible concentration of silicon.  相似文献   
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The kinetics of diffusion redistribution of phases within the system WSi2 W on heating tungsten silicide in air in the temperature range 1500-2000°C is studied. The stability and heat resistance of silicide coatings on tungsten is mainly governed by the diffusion of silicon towards the interphase boundaries W W5Si3, W5Si3 WSi2, and WSi2 SiO2, formation at them of diffusion barriers of lower silicide W5Si3, and also a protective SiO2 film at the outer boundary of the silicide coating. It is established that the transition rate for the higher to the lower tungsten silicide WSi2 W5Si3 is on average four times slower than the transition rate for MoSi2 Mo5Si3. It is shown that an increase in silicon concentration in the WSi2 surface layer stimulates formation of diffusion barrier compounds at interphase boundaries. This leads to an increase in the stability of the phase composition and heat resistance of a silicide coating on metals. In particular at 1700°C the transition rate for molybdenum silicide on tungsten MoSi2 (Mo, W)5Si3 is about twenty times slower than the transition rate for MoSi2 Mo5Si3, and less by a factor of about eleven than the transition rate for WSi2 W5Si3. Here there is also an increase in the heat resistance of silicide coatings on tungsten and molybdenum. It is shown that the SiO2 film on tungsten silicide does not lose its protective properties up to 2000°C.  相似文献   
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