Industrial interest of alumina-zirconia composites (ZTA Zirconia Toughened Alumina) is very well-known, especially for biomedical applications as orthopedics prosthesis. Combining the toughening by phase transformation of zirconia and the stability of the alumina matrix allows to reach better mechanical properties than the monolithic compounds. The dependence between mechanical properties and elaboration process makes the industrial production pretty complex. The first aim of this work in collaboration between Nanoe Company and the SPMS laboratory is the achievement of the production of ZTA with 2.5 to 50wt%. The second aim is the systematical study of microstructural, structural and mechanical properties of ZTA by focusing on the key parameters for the stability of the tetragonal phase. The developed industrial process leads to ZTA with densities above 99% and with very fine and well-dispersed microstructures. Both grain size materials depend on the composition in zirconia but did not depend on the yttria content in zirconia. Thanks to the comparison between microstructural, structural and mechanical properties, we identified several phenomenons. Excepting the variation of grain size and macrostrains due to the difference between coefficient of thermal expansion of alumina and zirconia, the alumina is more or less unaffected by the composite effect. Several phenomenons at different scale have an influence on the stability of tetragonal zirconia. At the lattice scale, the stabilizing effect of yttria is well-known. We identified another effect, the tensile stress applied by the alumina matrix destabilize the tetragonal zirconia. Even though, the retention of the tetragonal phase of unstabilized zirconia is achieved thanks to the inhibition of grain growth and the rigidity of the alumina matrix. The alumina matrix stabilizes the tetragonal zirconia at the grain scale. This observation allows us to determine that the critical grain size for spontaneous transformation for unstabilized zirconia ranges between 250 and 310nm. In the same way, the resistance of ZTA until 40wt% to the ageing indicates that the critical grain size for ageing for 3mol% yttria doped zirconia ranges between 310 and 360nm. In order to obtain the more efficient toughening by phase transformation and the better ageing resistance, we need to have an entire control of all these effects. This study concluded that the best compromise between toughening and ageing is achieved for ZTA with zirconia grain size below 300nm and doping between 1 and 2mol% of yttria.
