HIGH-TEMPERATURE PRECIPITATION HARDENING IN Y2O3 PARTIALLY-STABILIZEDZRO2 (Y-PSZ) SINGLE-CRYSTALS .3. EFFECT OF SOLUTE COMPOSITION AND ORIENTATION ON THE HARDENING

High temperature (1400 degrees C) precipitation hardening was studied for three Y2O3-partially stabilized ZrO2 (Y-PSZ) two-phase single crys tal alloys containing 3.4, 4.7 and 5.8 mol% Y2O3 that had been anneale d for up to 1000 h at 1600 degrees C along both a ''soft'' [112] and a ''hard'' [001] specimen orientation. Crystals with high load-bearing ability, greater than or equal to 400 MPa, were found for all conditio ns; the flow stress for the strongest crystals at 1400 degrees C excee ded 700 MPa. The high strength is related to the fact that any 1/2 [11 0] matrix dislocation in the cubic ZrO2 matrix is a partial in two of the three tetragonal ZrO2 variants present within coherent precipitate s, and that potent work hardening is present in this system. Age harde ning is observed in crystals deformed along [112], whereas age softeni ng is found for [001] crystals; this interesting difference arises fro m differences in dislocation-dislocation and dislocation-precipitate i nteractions in the two orientations.