The activation energies for Hf diffusion in pure W were found to be equal to 73kcal/mol for lattice diffusion and to 45kcal/mol for grain boundary diffusion, respectively. The presence of HfC restricted grain growth and thereby permitted diffusion measurements to be made over a wider range of temperatures while maintaining a relatively constant grain size of 10. It was found that the diffusion process was not greatly affected by the presence of HfC (80kcal/mol for lattice diffusion and 40kcal/mol for boundary diffusion). As expected, grain boundaries were found to enhance the observed diffusion at homologous temperatures of less than 0.5.

Y.Ozaki, R.H.Zee: Scripta Metallurgica et Materialia, 1994, 30[10], 1263-7