Enhanced hydrothermal resistance of Y-TZP ceramics through colloidal processing

Abstract

Two commercial zirconia powders with 3 mol% of yttria (TZ3YE and TZ3YS, labeled as ZE and ZS, respectively) sup- plied by Tosoh (Japan) were used for this study. Maximum colloidal stability for ZE was achieved by dispersing the pow- ders in a mixture of water/ethanol of 90:10 (wt/wt) using a sonication probe. The rheological behavior of the suspensions was optimized in terms of solids content ranging from 20 to 33 vol% and sonication time (0 – 6 min), the best results being obtained after 2 min. ZS samples were prepared to a solids loading of 30 vol% in water dispersing with 2 min-sonication. Samples obtained by slip casting in plaster molds were used for dynamic sintering studies, and fully dense and nanostructured specimens were obtained at temperatures of 1300 ° C – 1350 ° C (ZE samples) and 1400 ° C per 2 h (ZS samples). The Hardness ( H ) and Young’s Modulus ( E ) properties of the specimens were studied by nanoindentation technique giving 17 and 250 GPa mean values for H and E , respectively. The specimens were then forced to a low-temperature degradation (LTD) treatment at 130 ° C for 240 h in steps of 60 h. Raman spectroscopy and nanoindentation results of hydrothermally treated samples showed the absence of transformation from tetragonal to monoclinic phase until 180 h whereas the mechanical properties maintained constant even at the sample surface. After 240 h of LTD, the monoclinic phase was detected on all specimens by Raman peaks centered at 180, 191, and 383 cm 1 . The nanoin- dentation study revealed an important loss of mechanical fea- tures reaching 10 and 175 GPa for H and E , respectively. In the case of the ZS specimens, no monoclinic phase is detected after 240 h of LTD treatment and no decay of E or H is detected. The free defect microstructure reached for the ZS specimen revealed a higher hydrothermal resistance so that it is concluded that the excellent behavior against thermal degrada- tion is possible due to the large uniformity obtained by colloi- dal processing rather than the particle size of the starting powders