Laser Melting Processing of ZrO2-BaZrO3 Ceramic Eutectics

Abstract

Ceramic composites based on zirconia and barium zirconate are expected to possess good thermomechanical properties and mixed ionic (protons and oxide ions) transport properties. However, their processing by conventional sintering is difficult due to their refractoriness. This work reports the processing of a directionally solidified ZrO2-BaZrO3 eutectic by the laser floating zone (LFZ) method, with a focus on the effect of growth rates between 20 mm/h and 100 mm/h. X-ray diffraction and Raman spectroscopy data confirmed the presence of tetragonal ZrO2 and cubic BaZrO3 phases. Scanning electron microscopy reveals a fine eutectic microstructure, changing from coupled to colony-type morphology with increasing growth rate. Periodically spaced bands with a coarse eutectic microstructure are also observed. X-ray energy dispersive spectroscopy shows that the Y tends to occupy the ZrO2 lattice. Both ZrO2 and BaZrO3 phases display contiguity without interphase boundaries, according to impedance spectroscopy data. It is further shown that the ionic conductivity of the fibers is not influenced by the water vapour partial pressure, and it is slightly lower (9.7 x 10(-3) S cm(-1) at 824 degrees C) than for pure YSZ (ZrO2)0.97(Y2O3)(0.03) (1.6 x 10(-2) S cm(-1) at 800 degrees C). These results suggest that oxide ion transport through zirconia dominates the conduction mechanism, in agreement with the observed preferential location of yttrium in the zirconia phase.