On the transformation toughening of Y–ZrO2 ceramics with mixed Y–TZP/PSZ microstructures

Heat treatment of Y–TZP at high temperatures produces materials with a mixed Y–TZP/PSZ phase assemblage, which exhibit a unique combination of high mechanical strength and fracture toughness, uncommon in zirconia ceramics. The microstructure and crack growth resistance of the Y–TZP/PSZ materials developed by treating at 1650°C in air a fine-grained Y–TZP was studied. XRD as well as Raman spectroscopy results indicate that the obtained microstructure allow the retention of large tetragonal grains (up to ∼4 μm), resulting in both phase transformability enhancement and pronounced R-curve behavior. The large transformation zone, discerned from accurate measurements with Raman microprobe spectroscopy, sustains the above assessment and points out tetragonal to monoclinic phase transformation as the main toughening mechanism in the investigated Y–TZP/PSZ microstructures. This was confirmed by satisfactory agreement between the transformation toughening estimated from numerical analysis and the crack shielding experimentally determined from the R-curve measurements.