Phase composition and its changes during annealing of plasma-sprayed YSZ

The phase composition of plasma-sprayed yttria stabilized zirconia (YSZ), ZrO2 with 8% by mass Y2O3, was studied using neutron and X-ray diffraction. Comparison shows that neutron diffraction is superior for analysis of the phase composition as well as for the analysis of the yttria content of the tetragonal phase. The presence of large amounts of the cubic phase is probably often neglected or underestimated in standard XRD analysis due to scattering-related limitations and the inherent difficulty of the analysis. The importance of this fact needs to be addressed in future studies. The amount of monoclinic, tetragonal, and cubic phases was determined using neutron Rietveld refinement for feedstock powders, as-sprayed deposits and for samples annealed for 1 h at temperatures of 1100, 1200, 1300, and 1400°C. The two studied feedstock materials were manufactured by different production methods, and contained various amounts of the monoclinic phase depending on manufacturing method. While the tetragonal phase dominated, both feedstock powders also contained significant amounts of the cubic phase. The as-sprayed deposits were composed of mostly tetragonal phase, with only traces of the monoclinic phase; the amount of the cubic phase was reduced with respect to the feedstock. For one of the materials the cubic phase content remained significant (approx. 25% by mass), and for the other the cubic phase content was significantly lower (approx. 6% by mass). The cubic phase content after annealing at 1400°C was in both cases similar — approximately 40% by mass. There was no significant change in monoclinic phase content observed in this experiment. The yttria fraction within the tetragonal and cubic phases was followed and changes are discussed.