RELATIONSHIP BETWEEN FRACTURE-TOUGHNESS AND PHASE ASSEMBLAGE IN MG-PSZ

The phase content, size, and distribution have a marked effect on the thermomechanical properties of a 9 mol% MgO-ZrO2 (Mg-PSZ) alloy. The work undertaken in this study is the first investigation to simultaneously measure and characterize the quantitative bulk phase contents and correlate these parameters to the fracture toughness and R-curve behavior of a variously aged Mg-PSZ alloy. Quantitative bulk phase characterization entailed a systematic evaluation using neutron diffraction. In addition, microscopy techniques were used to determine the phase distribution and assemblage. The results indicate that the maximum toughness is attained, for a constant tetragonal precipitate size, when the anion-ordered delta-phase (Mg2Zr5O12) replaces a major portion of the cubic matrix phase after an 1100 degrees C aging treatment. The shape of the R-curve and the stress required to transform the tetragonal precipitates are also significantly influenced by the delta-phase content.