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

The distribution of tantalum in molybdenum and tungsten single crystals during electron beam floating zone melting under different 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 profiles 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. fluctuations of microscopic rate of growth occurred due to convection in the melt. The determined effective distribution coefficients of tantalum in molybdenum and tungsten approach to calculated theoretical values of the equilibrium distribution coefficient.