Multilayered Ceramic Constructs Created by EPD

摘要

Zirconia-based ceramics have gained considerable interest for several applications (e.g. solid electrolytes in fuel cells and in oxygen sensors, thermal barrier coatings and biomaterials for dental and orthopaedic applications) due to their high mechanical strength, improved fracture toughness and easy affordability. Zirconia occurs in three crystal modifications at low-pressure conditions: monoclinic, tetragonal and cubic. The monoclinic phase is the natural room temperature stable phase, while the tetragonal and the cubic phase can be stabilized at room temperature by doping with the right amount of some oxide dopants (e.g. CaO, MgO, CeO_2 and Y_2O_3). The stabilization of the tetragonal phase results in a remarkable increase in fracture toughness, whereas the stabilization of the cubic phase results in an increase of the ionic conductivity to values significantly higher than for other ceramics. In order to optimize the properties of the final ceramic by combining the high fracture toughness of the tetragonal phase of zirconia together with the high ionic conductivity of its cubic phase, we established an EPD layering process with nanometric sized powders of TZP with different mol percentages of yttrium oxide (3 % and 8 %) and produced multilayers of alternating tetragonal and cubic phases with a clearly defined interface. The crack propagation through this interface was studied by means of Vickers indentation.