The aging effect on the low temperature mechanical strength of 3.2YSZ single crystals manufactured by the Skull melting method

Single crystals of ZrO2 containing 3.2 mol% of Y2O3 were manufactured by the Skull melting method. The single crystals were composed of the t′-ZrO2 phase. For a comparison of the mechanical strength, 3 mol% of Y2O3 added tetragonal zirconia polycrystal (3Y-TZP) (Tosoh TZ-3Y®) samples were also prepared. The biaxial flexure strengths of the single crystal and 3Y-TZP ceramics were 1328±537 MPa and 1227±312 MPa, respectively. After autoclave treatment at 200 °C for 24 h, the strength of the single crystals and polycrystalline ceramics changed to 1345±251 MPa and 281±31 MPa, respectively. This result shows that the t′-ZrO2 single crystals have excellent resistance in moisture-enhanced mechanical degradation. Since the martensitic transformation of the tetragonal (t) and monoclinic (m) has crystallographic correspondences between the lattices, the relationship will lead to low interface energy at the t–m interface and high binding energy between the t and m phases. As far as the crystallographic relationship is maintained in the t′-ZrO2 single crystals, different from polycrystalline 3Y-TZP, the partial coherency seems to retard low temperature degradation – monoclinic phase pull out or crack generation – of single crystals.