Critical effect of cubic phase on aging in 3 mol% yttria-stabilized zirconia ceramics for hip replacement prosthesis

The isothermal tetragonal-to-monoclinic transformation of 3Y-TZP ceramics sintered at two different temperatures (1450°C and 1550°C) and duration (2 and 5 h) is investigated at 134°C in steam. Particular attention is paid to the presence of a cubic phase and its effect on isothermal aging. Sintering at 1550°C can result in a significant amount of large cubic grains in the specimens, that have a detrimental impact on aging resistance, especially for the first stage of the aging process. Cubic grains appear to be enriched in yttrium, which in turn leads to a depletion of yttrium in the neighboring tetragonal grains. These grains will act as nucleation sites for tetragonal-to-monoclinic transformation. Even for specimens sintered at lower temperature, i.e. 1450°C, the presence of a cubic phase is expected from the phase diagram, leading to a significant effect on aging sensitivity.