Effect of Yttria content and alumina addition on the formation of a textured microstructure during the surface nitridation of Yttria-stabilized tetragonal zirconia polycrystals (Y-TZP)

Abstract

The condition for the production of a textured microstructure was investigated in the process of nitridation of yttria-stabilized zirconia. The nitrided surface layer was composed of either columnar or equiaxed cubic grains. The amount of the cubic phase in the matrix, which was determined by yttria content and the sintering temperature, was the principal parameter that affected the morphology of the nitrided layer. With the increase in the cubic phase in the matrix, the chances of finding columnar grains decreased. The driving force of growth, which was provided by the free energy difference determined by the phase and grain size, decreased with the increase in the cubic phase in the matrix, and eventually led to the suppression of the growth of columnar grains. The cubic zirconia in the matrix also played the role of a transient pinning center due to its chemistry and lattice parameter that were dissimilar to those of the columnar grain. Such role of the cubic phase could be mimicked by the introduction of Al₂O₃ particles as an intended pinning center. With the introduction of the pinning center, the growth rate of the texture was suppressed and equiaxed grains appeared at the front of the texture. Therefore, by preparing the matrix with the utmost tetragonal phase, successful texturing of zirconia during nitridation could be achieved.