Experiments on Hf diffusion in W were carried out, at temperatures of between 1773 and 2573K, by using a secondary ion mass spectroscopic technique to determine the diffusional contribution to the coarsening process. The diffusion process at high temperatures was controlled by lattice diffusion, with an activation energy of 335kJ/mol, whereas that at low temperatures was governed by grain-boundary diffusion with an activation energy of 170kJ/mol. It appeared that the coarsening process was controlled by 2 energy barriers. One of these was dictated by the diffusivity of Hf, while the other was governed by the solubility limit as a function of temperature. The strain energy which was required in order to dissociate the carbide particles into individual species was also considered.

Y.Ozaki, R.H.Zee: Journal of Materials Science, 1995, 30[13], 3421-8