The low-temperature degradation of zirconia (ZrO 2 ) that was doped with 3 mol% yttria (Y 2 O 3 ) (3Y-TZP) was prevented by the heat treatment of sintered specimens in nitrogen. The heat treatment of sintered specimens resulted in a surface layer that was stabilized by nitrogen ions, whereas the interior was only slightly affected by the heat treatment. X-ray diffractometry and transmission electron microscopy analyses revealed that the stabilized surface layer consisted of cubic grains with tetragonal precipitates. Although the presence of the surface layer decreased the strength of the sintered 3Y-TZP, the strength of nitrified specimens was maintained when low-temperature annealing was applied.

Sintered tetragonal-zirconia polycrystals (TZP) were embedded in a zirconium nitride powder bed and heat-treated at various temperatures. Surface layers of the TZP specimens were transformed to a stabilized cubic-zirconia by nitrogen incorporation, and their thickness was observed to increase by a parabolic rate law. The nitrogen diffusivity was evaluated from the temperature dependence of the nitridation rate. The microstructure of the nitrided layer was composed of different zones of equiaxed and columnar grains. The columnar grains were developed along the nitrogen flux lines. The observed microstructural evolution was explained in terms of nucleation and growth kinetics of nitridation.

Raman spectroscopy has been used to obtain Raman spectra of yttria‐stabilized tetragonal zirconia subject to surface nitridation induced by contact with zirconium nitride. Raman spectra recorded from regions at increasing distance from the source of nitridation have been used to obtain diffusion profiles from samples treated at different times and temperatures. The coupling of X‐ray diffraction data previously taken and of the Raman spectra shows that in the samples there is a two‐phase region (tetragonal + cubic) near the nitrided surface and that, at larger distance inside the samples, there is only one phase (tetragonal). Fitting of the diffusive profiles in the single‐phase tetragonal region with an appropriate diffusion function allows the determination of the diffusion coefficient of nitrogen in tetragonal zirconia which is expressed in terms of the preexponential factor, D0= (3.98 ± 0.5) × 10−3 cm2/s, and the activation energy, Q= 170 ± 10 kJ/mol.

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