THE HAFNIUM-NITROGEN SYSTEM: PHASE EQUILIBRIA AND NITROGEN DIFFUSIVITIES OBTAINED FROM DIFFUSION COUPLES

摘要

Hafnium sheet and wedges were annealed in nitrogen atmosphere at temperatures of 1160-1800 ℃ and nitrogen pressures of 1-30 bar. The in situ diffusion couples were used to study the phase equilibria in the Hf-N system and for the determination of nitrogen diffusivities in η-Hf_3N_(2-x), ζ-Hf_4N_(3-x) and δ-HfN_(1-x), The activation energy of the nitrogen diffusion process is 2.7 eV in all three phases indicating an identical diffusion mechanism (migration via octahedral nitrogen vacancies). It is shown that wedge-type diffusion couples can be used to measure homogeneity regions of line compounds (e.g. by EPMA) more accurately.