Interdiffusion in the Nickel–Tungsten and Thoria-Dispersed Nickel–Tungsten Systems

The interdiffusion coefficient in the α solid solution of tungsten in nickel has been determined for the nickel–tungsten and TD (thoria-dispersed) Nickel–tungsten systems over the range 1000–1316° C. The Boltzmann–Matano analysis was employed to compute diffusivities from concentration vs. penetration curves measured with the electron microanalyser. The interdiffusion co-efficient is concentration-dependent in the nickel–tungsten system, decreasing with increasing tungsten content and can be represented by the equation: D ~ = 1·19 exp ( − 0·0469 C w ) exp ( − 3·69 × 10 4 ) T The data at low solute concentrations agree well with literature values and are consistent with a vacancy mechanism for diffusion. Interdiffusion in the TD Nickel–tungsten system is concentration-dependent and shows a bimodal temperature-dependence. The high-temperature behaviour is explained on the basis of a vacancy mechanism, while the behaviour at lower temperatures suggests enhanced diffusion due to short-circuiting diffusion paths. A large Kirkendall effect in TD Nickel/tungsten diffusion couples indicates that nickel is the more rapidly moving species.