The flexural strength of yttria-partially stabilized zirconia was eval
uated as a function of temperature (20-1000 degrees C in air), applied
stress and time. The material was susceptible to strength degradation
at low temperatures (200 and 300 degrees C) due to the phase transfor
mation of the tetragonal structure to monoclinic, possibly accompanied
by microcracking. In this temperature range, the material was incapab
le of sustaining low applied stress levels of 276 MPa for any signific
ant duration (> 100 h < 500 h). Stress rupture testing at 600 degrees
C and above identified the onset of viscous flow of the glassy phase a
nd consequent: degradation of material strength.