FEATURES OF NOTCH PREPARATION FOR FRACTURE-TOUGHNESS MEASUREMENTS IN PARTIALLY-STABILIZED ZIRCONIA

Fracture toughness measurements with the use of saw cut notches or ind entation flaws often give overestimated K-Ic values when the flaws are introduced into sintered bodies which contain a metastable phase. Not ching before sintering offers a way to eliminate the problem of residu al stresses generated by flaw preparation, as has been demonstrated wi th yttria-partially-stabilized tetragonal zirconia. However, the respo nse of each new material to the notching procedure in the unsintered s tage has to be considered carefully to exclude possible effects of loc ally changed densification and grain-growth kinetics. Untransformable alumina microstructures show similar K-Ic values as determined by ISB and SENB methods with O.1-mm narrow notches introduced in the green st ate, and similar K-Ic values measured with notches of the same width i ntroduced before and after sintering. Notches introduced before sinter ing generate the well-known, rather strong notch width influence on K- Ic in the notch width range between 0.1 and 0.2 mm.