Tracer diffusion in tungsten

Abstract

Measurements of the lattice diffusion coefficients for Nb, Ta, and W isotopes in tungsten were made over the temperature range 1300–2400°C using standard tracer methods in combination with anodic-film sectioning techniques. The data indicated that the Arrhenius relation was obeyed over the entire temperature range, and the following analytical expressions were obtained: D(Nb) = 3.01 exp (−137,600/ RT) cm 2/sec D(Ta) = 3.05 exp (−139,900/ RT) cm 2/sec D(W) = 1.88 exp (−140,300/ RT) cm 2/sec. The characteristics exhibited by the penetration profiles of both single- and polycrystalline specimens emphasized the need for sensitivity and completeness in the data used for the determination of both lattice and short-circuit diffusion parameters. When measuring lattice diffusion coefficients, even in single crystals, it was found that the section thickness must be kept smaller than √( Dt) to minimize the effects of short-circuit paths. Conversely, in the region of the profile governed by short-circuit effects, extensive sets of data could not be described in terms of a simple model leading to a unique diffusion coefficient.