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 Y ₂O₃ 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^R) 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′-ZrO ₂ 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.