Features of notch preparation for fracture toughness measurements in partially stabilized zirconia.

Fracture toughness measurements with the use of saw cut notches or indentation flaws often give overestimated KIc when the flaws are introduced into sintered bodies which contain a meta-stable phase. Notching before sintering offers a way to eliminate the problem of residual stresses generated by flaw preparation, as it is demonstrated with partially Y2O3-stabilized tetragonal zirconias. However, the response of each new material to the notching procedure in the unsintered stage has to be considered carefully to exclude possible effects of locally changed densification and grain growth kinetics. Untransformable Al2O3 microstructures show (i) similar KIc determined by ISB and by SENB with 0.1 mm narrow notches introduced in the green state, (ii) similar KIc measured with notches of the same widths when introduced before and after sintering, respectivly. Notches introduced before sintering generate the well known, rather strong notch width influence on KIc in the notch width range betwee n 0.1 and 0.2 mm .