EFFECTS OF HIGH-TEMPERATURE- AND HIGH-PRESSURE-WATER ON THE LOW TEMPERATURE DEGRADATION BEHAVIOUR OF Y-TZP.

The effects of high-temperature (200 degree -800 degree C)- and high-pressure (5 or 100 MPa)-water on the low-temperature degradation behavior of Y-TZP were investigated. Tetragonal (t) to monoclinic (m) transformation is markedly accelerated by the existence of water, under the hydrothermal condition at 200 degree -300 degree C, the surface of the specimen is spalled by the stress accompanied by the expansion of t yields m transformation. The spalled layers and the surfaces of the unspalled bulk specimen consist of almost m-phase ( approximately equals 90 vol%). From SEM observation on these specimens, large cracks occurred from the corner of the specimen by the stress concentration, and then they propagated parallely to the surface of the specimen and caused the spalling.