Aging resistance and fracture toughness of ceria–infiltrated zirconia

Abstract

The main drawback of yttria stabilized zirconia (3Y-TZP) is represented by the Low Temperature Degradation (LTD), which consists in the progressive transformation of the tetragonal phase, metastable at room temperature, to the stable monoclinic phase, when the material is exposed to humid environment and moderate temperatures. LTD is responsible for a decrease in superficial mechanical properties for relatively short exposure times, while bulk properties are affected for longer exposures. These effects have limited the use of 3Y-TZP in biomedical devices during the last years. A process based on the addition of ceria, a stabilizer of tetragonal phase less susceptible to LTD, has been recently developed. A solution of Cerium salts is infiltrated into the ceramic piece at the porous pre-sintered state. After sintering, ceria diffuses into zirconia lattice. In a first stage, the process was optimized in terms of LTD resistance, maintaining the microstructure, strength and hardness of 3Y-TZP. Nevertheless, a slight decrease in indentation fracture toughness was recorded. In a second stage, the research has been focused on the possibility of compensating the toughness decrease by sintering at higher temperature, obtaining a moderate increase in grain size without prejudicial effects on the LTD resistance achieved with ceria addition.