Mechanical properties of cellular ceramics obtained by gel casting: characterization and modeling

Dense and cellular ceramics were produced from yttria partially stabilized zirconia powders by gel-casting, using agar as a gelling agent and polyethylene spheres (125–300 μm diameter) as volatile pore forming agent to create 50–65 vol.% spherical macropores, uniformly distributed in a microporous matrix. The mechanical properties of both dense and porous samples were investigated at the microscale by nanoindentation testing. The influence of micro-porosity on the mechanical properties of samples was evaluated by the analysis of hardness and modulus depth profiles, coupled with FIB-SEM section observations of selected indentation marks. The intrinsic elastic modulus of the zirconia phase resulted to be of the order of 220 GPa. Mechanical characterization at the macroscale consisted of uniaxial compression tests and four point bending tests. Elastic moduli of about 170 GPa were measured for about 93% dense ceramics, lowering down to 44 and 13 GPa with the addition 50 and 65 vol.% macropores, respectively. Digital image based finite element analysis (DIB-FEA) procedures were implemented in order to verify their applicability for the prediction of mechanical behavior of this type of cellular materials: results confirmed that a very good match between measured and calculated values of elastic modulus can be achieved, provided that the effects of micro-porosity are considered by the proper choice of the elastic properties to be assigned to each individual phase identified by Image Analysis.