Microstructural design and elaboration of multiphase ultra-fine ceramics

Three-phase composites in the system Al2O3–YAG–ZrO2 (AYZ) were produced by doping the surface of commercial alumina nanopowders with inorganic precursors of the second phases. Materials with three different compositions were prepared, in which 5, 20 and 33 vol.% of each second phase were respectively present. Pure crystalline phases were obtained in the final composites, as assessed by X-ray diffraction. Green bodies were produced by slip casting and uniaxial pressing. Subsequent free sintering led to full densification and to highly homogeneous microstructures, in terms of grain size and second phase distribution. A progressive refinement of the alumina matrix grain size was achieved by increasing the second phase content, varying from micro/nano-composites to ultra-fine structures, with a mean grain size of about 500 nm for all the phases. The three materials presented high Vickers hardness values, as a results of the high final density and ultra-fine, homogeneous microstructures.