Wear behaviour, fluorescence and SEM investigations on nanocomposite zirconia-toughened alumina

The need to improve the reliability of alumina and zirconia hip prostheses has led to the development of zirconia-toughened alumina (ZTA) ceramics. The set-up of new colloidal processing routes brought about new ZTA nanocomposites (NZTA) with a significantly smaller and narrower particle size distribution of zirconia than conventional powder mixing methods. These nanocomposites present reinforcement mechanisms other than transformation toughening, mainly based on residual thermal stresses. In this study, the wear behaviour of NZTA–NZTA couplings was evaluated in a hip joint simulator run for seven million cycles, in comparison with commercial and experimental alumina couplings. From a statistical point of view, the three sets of specimens did not show significant differences in wear behaviour. However, from a gravimetric point of view, the weight loss decreased along the series: experimental alumina > NZTA > commercial alumina. The R1 and R2 fluorescence bands (due to the Cr3+ ions naturally present in alumina ceramics as trace impurities) increased in intensity along the series: experimental alumina < NZTA < commercial alumina, indicating a progressive improvement of the surface quality. SEM analysis confirmed that the better the sample finishing, the better was the wear behaviour. By taking into account that the tested NZTA samples were prototypes (thus with a surface finishing worse than for a production type), it can be stated that NZTA can offer the option of improving the lifetime and reliability of ceramics.