HIGH-TEMPERATURE PRECIPITATION HARDENING OF Y2O3 PARTIALLY-STABILIZED ZRO2 (Y-PSZ) SINGLE-CRYSTALS

Precipitation hardening in two-phase 4.5 m/o Y2O3 partially-stabilized ZrO2 (Y-PSZ) single crystals has been studied at 1400°C, using crystals aged at 1600°C for various times up to 150 h. This aging allowed the formation and growth of low-solute tetragonal (t)-ZrO2 precipitates in a high-solute cubic (c)-ZrO2 solid solution matrix. These colony precipitates are internally twinned on {110}, and form fiber-like morphologies (fiber axis along 001 direction) at the longest annealing times; the lamellar spacing within the colonies coarsens via conventional Ostwald ripening. Surprisingly, even large precipitates (> 1 μm long) are coherent. All crystals deformed by nucleation and propagation of Luders bands, leading to serrated flow. The yield stress increases linearly with lamellar spacing and reaches the high value of 550 MPa (at 1400°C) for the 150 h sample. The particular dislocation-precipitate interactions leading to this potent precipitation hardening are discussed.