R-CURVE BEHAVIOR AND FLAW INSENSITIVITY OF CE-TZP AL2O3 COMPOSITE/

A ceria-partially-stabilized zirconia-alumina (Ce-TZP/Al2O3) composite optimized for transformation toughening was used to demonstrate its f law insensitivity due to R-curve behavior. Four-point bend specimens f abricated with a controlled distribution of spherical pores showed nea rly the same characteristic strength and strength variability (Weibull modulus) as specimens fabricated without the artificial pores. In sit u observations confirmed stable growth of cracks initiated at pores an d the crack lengths at fracture instability were much greater than the pore sizes, thus resulting in fracture strengths insensitive to the p ores. The small variability in the fracture strength was found to be a ssociated with variability in the R-curve and the instability crack le ngths. An analysis based on the fracture instability criterion for ris ing crack growth resistance accounted for the strength variability due to variability in the R-curve. Comparable four-point bend experiments were also conducted on a sintered yttria-partially-stabilized zirconi a (2Y-TZP) ceramic. This ceramic showed significant degradation of str ength due to the presence of the pores. This flaw sensitivity is attri buted to its steep rising R-curve over short crack lengths.