The effect of crystallization conditions on tantalum distribution in molybdenum and tungsten during electron beam zone melting

Abstract

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