The titanium nitride used in this stud), (6-TiN~ phase) was either single crystal with an initial composition of TiNo.82 or polycrystal with a composition of TiNo.94.
Nitrogen self-diffusion was investigated by the method of gas-solid isotope exchange in the 800Β°C to 1650Β°C temperature range in samples thermodynamically equilibrated by preliminao' annealing. The annealing time for the diffusion was about a few hours and the nitrogen 15 pressure was constant and equal to O" 7 atm.
The concentration profiles of nitrogen 15 were measured by secondary ion mass spectrometry (SIMS). These profiles show two slopes which correspond to a fast decrease .for short penetration depths (about 100 nm) followed by a slower decrease [or depths up to about a few microns at 1650Β°C for 2 hours of d.i[:fusion. These observations were interpreted in terms of bulk diffusion and short-circuit diffusion. For the bulk diffusion, the adopted solution was an erf pro.file corresponding to Fick's law for a constant superficial concentration and for the shortcircuit diffusion, the solution of Whipple was appl#d.
For poO, co,stals, the bulk diffusion coefficients D and grain boundart' diffusion coefficients D' can be described by: