Nanomechanical and Topographical Characterization of Zirconia-Toughened-Alumina Composites

Objectives: To characterize the effects of aging on the nanomechanical properties and topographical parameters of an experimental Zirconia Toughened Alumina (ZTA) composite compared with a second-generation dental zirconia.
Methods: Disk-shaped specimens of two materials: 1) ZTA-70/30 (70% alumina reinforced with 30% second-generation 3Y-TZP) and 2) Zpex (Second-generation 3Y-TZP) were produced for characterization before and after aging (n=10/material, 12x1 mm). After synthesized, ceramic powders were pressed, and green-body samples were sintered and polished. Nanoindentation testing was used to record elastic modulus (E) and hardness (H) of both groups. Interferometry was performed to assess 3D surface roughness parameters (S_a, S_q), while the crystalline content and microstructure of the materials were evaluated through X-ray diffraction (XRD) and scanning electron microscope (SEM). All tests were performed before and after simulated aging (134 C, 2.2 bar, 20 hours). Statistical analyses were performed using linear mixed-model and least square difference pos-hoc tests (a=5%).
Results: XRD spectra indicated stability of the monoclinic peaks for ZTA-70/30 (~2.5%) and an increment of the monoclinic content for Zpex (~18%) after aging. SEM imaging evidenced the achievement of a dense surface with homogeneous distribution of zirconia particles in the alumina matrix for ZTA and a dense surface with regular zirconia grains for Zpex. Aging did not affect the surface roughness parameters of ZTA-70/30, however, a significant increase in S_a was recorded for Zpex following aging (~90 nm). Finally, ZTA-70/30 yielded highest H and E values (H: 13 GPa, E: 214 GPa) when compared to Zpex (H:11 GPa, E: 167 GPa), and these values remained consistent after aging for both groups.
Conclusions: ZTA-70/30 presented high hydrothermal stability at all variables tested, where artificial aging significantly increased the monoclinic content and surface roughness of Zpex.