Effect of alumina-doping on grain boundary segregation-induced phase transformation in yttria-stabilized tetragonal zirconia polycrystal

The microstructure in a small amount of Al2O3-doped Y2O3-stabilized tetragonal zirconia polycrystal (Y-TZP) sintered at 1100-1650 degrees C was examined to clarify the effect of Al3+ ions segregated at grain boundaries on cubic-formation and grain-growth processes. The sintering rate in Y-TZP was remarkably enhanced by Al2O3-doping. In addition, at temperatures >1500 degrees C, grain growth remarkably proceeded, and the fraction of the cubic phase increased in comparison with that of undoped Y-TZP. High-resolution electron microscopy and nanoprobe x-ray energy dispersive spectroscopy measurements revealed that no amorphous layer existed along the grain-boundary faces in Al2O3-doped Y-TZP and that Y3+ and Al3+ ions segregated at grain boundaries over widths of similar to 10 and similar to 6 nm, respectively. At 1100 degrees C, Al3+ ions started to segregate at grain boundaries, and the segregation peak of Al3+ ions increased as the sintering temperature increased. Cubic-formation and grain-growth behaviors in Al2O3-doped Y-TZP were reasonably interpreted by taking into account the effect of Al3+ ions segregating along grain boundaries.