STRENGTH CHARACTERIZATION OF MGO-PARTIALLY STABILIZED ZIRCONIA

The flexural strength of MgO-partially stabilized zirconia was evaluated as a function of temperature (20-1300-degrees-C in air environment), applied stress and time. The indentation-induced-flaw technique did not produce well-defined symmetrical cracks of controlled size, whose length (on the tensile surface) or depth (on the fracture face) can be measured unambiguously, and therefore it should not be used for measuring fracture toughness. The sudden decrease in fracture strength at moderately low temperatures (200-800-degrees-C) is believed to be due to stability of the tetragonal phase and relative decrease in the extent of the stress-induced martensitic phase transformation of the tetragonal to monoclinic phase. Flexural stress rupture testing at 500-800-degrees-C in air indicated the material's susceptibility to time-dependent failure, and outlines safe applied stress levels for a given temperature. Stress rupture testing at 1000-degrees-C and above at low applied stress levels showed bending of specimens, indicating the onset of plasticity of viscous flow of the glassy phase and consequent degradation of material strength.