Influences of nano-3Y-TZP reinforcement on phase transformation and crystallite size modification of zirconia-toughened alumina and Rietveld refinement of crystallographic data

The effects of varying amount of nano-3 mol% yttria-stabilized zirconia addition on the crystal structures, mechanical, and microstructural properties of zirconia-toughened alumina (ZTA) composite have been investigated in this work. The ZTA specimens were prepared by different 3Y-TZP amount ranging from 9 to 18 wt.% and sintered at 1550 °C for 2 h. The densification behaviour, indentation fracture toughness, microhardness, elastic modulus, flexural strength and surface morphology of the composites have been determined and correlated with tetragonal → monoclinic phase transformation and retention of tetragonal phase. Rietveld refinement of the crystallographic data was performed to correlate the effect of zirconia addition on the phase compositions, t → m transformability and impacts on crystallite sizes and lattice parameter. The toughness and flexural strength of the composites improved significantly up to 15 wt.% YSZ addition followed by a reduction for 18 wt.%, while the hardness and elastic modulus decreased with YSZ addition. Rietveld refinement ascertains the metastable t-ZrO 2 retention and thermodynamically stable m-ZrO 2 transformation with increasing 3Y-TZP and subsequent enhancement in fracture toughness through transformation toughening.