Processing of alumina-coated tetragonal zirconia materials and their response to sliding wear

Alumina-coated tetragonal zirconia stabilised with 3 mol% of Y2O3 (YTZP) specimens (30 mm × 30 mm × 6 mm) have been obtained by dipping of pre-sintered YTZP compacts in alumina suspensions and subsequent sintering. The coated specimens present hardness values and a wear resistance similar to those of reference dense alumina specimens and significantly higher than those of the YTZP substrates.The optimisation of the processing parameters is described. First, YTZP compacts with different open porosity levels were fabricated by colloidal filtration and subsequent thermal treatment at temperatures ranging from 1100 to 1400 °C. Coated compacts were obtained by dipping the porous ones in alumina suspensions prepared in ethanol with two different solid loadings: 3 and 10 vol.%, during immersion times up to 40 min. Sintering (1500 °C–2 h) of the coated compacts was performed and microstructural analysis allowed the selection of the optimum porosity levels for the YTZP substrates and dipping conditions. For the optimised conditions, YTZP plates (30 mm × 30 mm × 6 mm) were coated and the thermal treatment to reach densification of the substrate and the coating was optimised. Relatively thick coatings (≅200 μm) were obtained. Hardness and wear resistance were evaluated for sintered monolithic and coated YTZP compacts and an alumina reference material and the wear damage of the tested specimens was analysed.