Silica infiltration in partially stabilized zirconia: Effect of hydrothermal aging on mechanical properties

It aimed to evaluate if silica infiltration might influence the hydrothermal degradation of zirconia by determining: the phases formed, hardness, microstructure, and flexural strength of a 3Y-TZP. Yttria partially stabilized zirconia discs (1.2 mm thickness x 13 mm diameter) (InCeram YZ, Vita Zanhfabrik) were produced and assigned into 6 groups, considering 2 factors: silica infiltration in 2 levels (as-sintered or infiltration) and hydrothermal aging (LTD-Low Temperature Degradation) in 3 levels (baseline, aging at 132 °C for 35 h or 140 h). All the groups were subjected to the biaxial flexural test (n = 30), and Vickers hardness (n = 42). Weibull analysis was performed to determine the Weibull moduli (m) and characteristic strenghts (σ₀). The specimens were characterized by scanning electron microscopy (SEM) to evaluate microstructure and X-ray diffraction (XRD) for phases percentages determination. For as-sintered condition: there was saturation of the amount of monoclinic zirconia after 35 h of hydrothermal aging, with 66% of monoclinic zirconia formed on the surface. LTD generated a progressive reduction in hardness over time; flexural strength was increased by the 35-h treatment (baseline: 974 MPa; 35 h: 1161.5 MPa), but, the 140 °C treatment was deleterious (698.5 MPa). On the other hand, the infiltrated specimens had an increase in the amount of cubic zirconia on the surface and showed 26% (35h) and 31% (140h) of monoclinic zirconia after the hydrothermal aging ; the strength was kept unaltered after LTD-35 h (935.9 MPa) and an increase was observed after LTD-140 h (1033.6 MPa); the hardness values had no statistically significant changes during the process. Thus, one can concludes that the silica infiltration can prevent the decrease in the mechanical properties due to the LTD on partially stabilized zirconia materials.