Ytterbia–neodymia–costabilized TZP—Breaking the limits of strength–toughness correlations for zirconia?

TZP ceramics were manufactured by hot pressing of pyrogenic zirconia nanopowder which was costabilized by 1 mol% ytterbia and 2 mol% neodymia (1Yb–2Nd–TZP) via the nitrate route. The evolution of microstructure, phase composition and mechanical properties with variation of sintering temperature from 1200 °C to 1400 °C was investigated. 1Yb–2Nd–TZP consists of a bimodal microstructure of small very transformable tetragonal grains and large cubic grains. At intermediate sintering temperature the materials combine a bending strength of 1250 MPa with a fracture resistance >13 MPa √m. The high threshold stress intensity of 7 MPa √m indicates high resistance to subcritical crack growth. An increase in fracture resistance before the crack tip induced by compressive residual stress shifts the strength–toughness correlations to higher values than previously considered possible.