The distribution of tantalum in molybdenum and tungsten single crystals during electron beam fl oating zone meltingunder diff erent crystallization conditions was investigated. The performed line chemical analysis of specimensproved creation of tantalum micro segregation, so-called growth striations, which showed themselves on concentrationproĀ les as periodically alternating areas with increased and decreased concentrations of tantalum. The existenceof these chemical inhomogeneities suggests that stationary conditions of the crystal growth were disturbedduring the zone melting, i.e. fl uctuations of microscopic rate of growth occurred due to convection in the melt. Thedetermined eff ective distribution coeffi cients of tantalum in molybdenum and tungsten approach to calculatedtheoretical values of the equilibrium distribution coeffi cient.
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